Final Flashcards
Asexual reproduction
a single parent gives rise to offspring that are genetically identical to the parent (unless mutations occur).
a single parent may split, bud, or fragment to give rise to two or more offspring.
budding
a small part of the parent’s body seperates from the rest and develops into a new individual. Sometimes buds remain attached and become more or less independent members of a colony.
Fragmentation
The body of the parent breaks into several pieces; each piece regenerates the missing parts and develops into a whole animal.
Parthenogenesis (“virgin development”)
a form of asexual reproduction in which an unfertilized egg develops into an adult animal, typically haploid (adult).
Internal fertilization
male generally dlivers sperm cells directly into the females body. Her moist tissue provide the watery medium required for the movement of the sperm, and gametes fuse inside the body.
external fertilization
(aquatic) gametes meet outside the body. Mating partners usually release eggs and sperms into water simultaneously. Gametes live for a short time, many lost in water, and some are eaten by predators. Sufficient numbers still meet to perpetuate the species.
spermatogenesis
the process of sperm cell production
takes place within the seminiferous tubules
begins with undifferentiated cells, the spermatogoia in walls of tubules
testes
male gonads
seminiferous tubules
a vast tangle of hollow tubules, within each testis.
spermatogonia
undifferentiated cells in the walls of the tubules
diploid cells
divide by mitosis and produce more spermatogonia.
primary spermatocytes
undergo meiosis and produce haploid gamettes.
Undergoes 1st meiotic division –> produces 2 haploid secondary spermatocytes –> during 2nd meiotic each of the 2 secondary spermatocytes givrs rise to 2 haploid spermatids
spermatids
4 spermatids are produced from original primary spermatocyte. Each spermatid differentiates into a mature sperm.
acrosome
a caplike structure covering the head of a sperm cell that is capable of releasing an enzyme (proteolytic –> protein-digestiong) so that the sperm may penetrate the outter covering of the egg.
Sertoli cells
supporting cells of the tubules of the testis.
ring the fluid filled lumen of the seminiferous tubule
provide nutrients for developing sperm
secrete hormones and other signaling molecules
joined to one another by tight junctions at a place just within the outer membrane of the tubule.
tight junctions form compartments that seperate sperm cells in various stages of development.
scrotum
a skin covered sac suspended from the groin.
serves as a cooling unit, maintaining sperm below body temperature.
epididymis
A coiled tube that receives sperm from the testis and conveys it to the vas deferns suring ejaculation.
sperm finishes maturing here and is stored.
Vas deferens
One of the paired sperm ducts that connects the epididymis of the testis to the ejaculatory duct.
Ch. 50 ejaculatory duct
passes through the prostate gland and then opens into the single urethra.
urethra
the tube that conducts urine from the bladder to the outside of the body
and in males sperm as well
seminal vesicles
(paired) secrete a fluid rich in fructose and prostglandins into the vasa deferentia.
fructose provides energy for ejaculated spern.
Prostaglandins stimulate contractions of smooth muscle in both male and female reproductive racts. THese contractions help in transportation through reproductive tracts.
prostate gland
(single) secretes an alkaline fluid that neutralizes the acidic secretions of the vagina.
also contains clotting enzymes and prostate-specific antigen (PSA).
bulbourethral glands
located on each side of the urethra
during sexual arousal, releases a mucous secretion. This fluid lubricates penis for penetration into vagina.
ecology
the study of how living organisms and the physical environment interact in an immense and complicated web of relationships.
biotic factors
the interactions among organisms
abiotic facors
interactions between organisms and their nonliving, physical environment. Include precipitation, temperature, pH, wind, and chemical nutrients.
Environmental science
a scientific discipline with ties to ecology, focuses on how humans interact with the environment.
population
a group consisting of members of the same species that live together in a prescribed area at the same time.
Population ecology
considers both the number of individuals of a particular species that are found in an area and the dynamics of the population.
Population dynamics
the study of changes in populations—how and why those numbers increase or decrease over time.
Population density
the number of individuals of a species per unit of area or volume at a given
may be determined in large part by biotic or abiotic factors in the environment that are external to the individuals in the population.
Random dispersion
occurs when individuals in a population are spaced throughout an area in a manner that is unrelated to the presence of others
Of the three major types of dispersion, random dispersion is least common and hardest to observe in nature, leading some ecologists to question its existence.
clumped dispersion
most common spacing clumped, also called aggregated distribution or patchiness, which occurs when individuals are concentrated in specific parts of the habitat. Clumped dispersion often results from the patchy distribution of resources in the environment. It also occurs among animals because of the presence of family groups and pairs, and among plants because of limited seed dispersal or asexual reproduction. Clumped dispersion may sometimes be advantageous because social animals derive many benefits from their association.
Uniform dispersion
occurs when individuals are more evenly spaced than would be expected from a random occupation of a given habitat. Uniform dispersion also occurs when competition among individuals is severe, when plant roots or leaves that have been shed produce toxic substances that inhibit the growth of nearby plants, or when animals establish feeding or mating territories.
Some populations have different spacing patterns at different ages.
What two factors, expressed on a per capita (that is, per individual) basis: ultimately cause change on a global scale?
Population size changes over time. On a global scale, this change is ultimately caused by two factors, expressed on a per capita (that is, per individual) basis: natality, the average per capita birth rate, and mortality, the average per capita death rate.
In humans the birth rate is usually expressed as the number of births per 1000 people per year and the death rate as the number of deaths per 1000 people per year.
Equations
The growth rate of a local population must take into account birth rate (b), death rate (d), immigration rate (i), and emigration rate (e) on a per capita basis. The per capita growth rate equals the birth rate minus the death rate, plus the immigration rate minus the emigration rate:
(4) r= (b-d)+(i-e)
In equation (1), ∆N is the change in the number of individuals in the population, ∆t the change in time, N the number of individuals in the existing population, b the natality, and d the mortality.
(1) ∆N/∆t =N(b-d) or can write w/out the N.
The growth rate (r), or rate of change (increase or decrease) of a population on a per capita basis, is the birth rate minus the death rate:
(2) r=b-d
instantaneous growth rate (dN/dt). (The symbols dN and dt are the mathematical differentials of N and t, respectively; they are not products, nor should the d in dN or dt be confused with the death rate, d.) Using differential calculus, this growth rate can be expressed as follows:
(3) dN/dt=rN
where N is the number of individuals in the existing population, t the time, and r the per capita growth rate.
dispersal
movement of individuals among populations, must be considered when examining changes in populations on a local scale.
intrinsic rate of increase (rmax)
The maximum rate at which a population of a given species could increase under ideal conditions, when resources are abundant and its population density is low, is known as its intrinsic rate of increase (rmax).
A particular species’ intrinsic rate of increase is influenced by several factors. These include the age at which reproduction begins, the fraction of the lifespan (duration of the individual’s life) during which the individual is capable of reproducing, the number of reproductive periods per lifetime, and the number of offspring the individual is capable of producing during each period of reproduction. These factors determine whether a particular species has a large or small intrinsic rate of increase.
exponential population growth,
If we plot the population size versus time, under optimal conditions, the graph has a J shape that is characteristic of exponential population growth, which is the accelerating population growth rate that occurs when optimal conditions allow a constant per capita growth rate. When a population grows exponentially, the larger that population gets, the faster it grows.
carrying capacity (K)
represents the largest population that can be maintained for an indefinite period by a particular environment, assuming there are no changes in that environment.
logistic population growth
When a population regulated by environmental limits is graphed over longer periods, the curve has a characteristic S shape. The curve shows the population’s initial exponential increase (note the curve’s J shape at the start, when environmental limits are few), followed by a leveling out as the carrying capacity of the environment is approached. The S-shaped growth curve, also called logistic population growth, can be modeled by a modified growth equation called a logistic equation. The logistic model of population growth was developed to explain population growth in continually breeding populations. Similar models exist for populations that have specific breeding seasons.
The logistic model describes a population increasing from a small number of individuals to a larger number of individuals that are ultimately limited by the environment. The logistic equation takes into account the carrying capacity of the environment:
(5) dN/dt=rN[(K-N)K]
density-dependent factor
Sometimes the influence of an environmental factor on the individuals in a population varies with the density or crowding of that population. If a change in population density alters how an environmental factor affects that population, then the environmental factor is said to be a density-dependent factor.
competition
an interaction among two or more individuals that attempt to use the same essential resource, such as food, water, sunlight, or living space, that is in limited supply.
Competition occurs both within a given population (intraspecific competition) and among populations of different species (interspecific competition).
interference competition
Individuals of the same species compete for a resource in limited supply by interference competition or by exploitation competition. In interference competition, also called contest competition, certain dominant individuals obtain an adequate supply of the limited resource at the expense of other individuals in the population; that is, the dominant individuals actively interfere with other individuals’ access to resources.
species in which interference competition operates experience a relatively small drop in population size, caused by the death of individuals that are unable to compete successfully.
exploitation competition
In exploitation competition, also called scramble competition, all the individuals in a population “share” the limited resource more or less equally so that at high population densities none of them obtains an adequate amount. The populations of species in which exploitation competition operates often oscillate over time, and there is always a risk that the population size will drop to zero.
density-independent factor
Any environmental factor that affects the size of a population but is not influenced by changes in population density is called a density-independent factor. Such factors are typically abiotic. Random weather events that reduce population size serve as density-independent factors.
semelparous
Species that expend their energy in a single, immense reproductive effort
iteroparous
exhibit repeated reproductive cycles—that is, reproduction during several breeding seasons— throughout their lifetimes.
life history traits
Ecologists try to understand the adaptive consequences of various life history traits, such as semelparity and iteroparity. Adaptations such as reproductive rate, age at maturity, and fecundity (potential capacity to produce offspring), all of which are a part of a species’ life history traits, influence an organism’s survival and reproduction.
Although many different life histories exist, some ecologists recognize two extremes: r-selected species and K-selected species.
fitness
The ability of an individual to reproduce successfully, thereby making a genetic contribution to future generations of a population, is called its fitness
r selection
Populations described by the concept of r selection have traits that contribute to a high population growth rate. Recall that r designates the per capita growth rate. Because such organisms have a high r, biologists call them r strategists or r-selected species. Small body size, early maturity, short lifespan, large broods, and little or no parental care are typical of many r strategists, which are usually opportunists found in variable, temporary, or unpredictable environments where the probability of long-term survival is low. Some of the best examples of r strategists are insects & plants.
K selection
In populations described by the concept of K selection, traits maximize the chance of surviving in an environment where the number of individuals is near the carrying capacity (K) of the environment. These organisms, called K strategists or K-selected species, do not produce large numbers of offspring. They characteristically have long lifespans with slow development, late reproduction, large body size, and a low reproductive rate. K strategists tend to be found in relatively constant or stable environments, where they have a high competitive ability. Animals that are K strategists typically invest in parental care of their young.
life table
A life table can be constructed to show the mortality and survival data of a population or cohort,
a group of individuals of the same age, at different
times during their lifespan.
Survivorship
EX: Drummond phlox –> type 1
herring gull –> type varies
Survivorship is the probability that a given individual in a population or cohort will survive to a particular age. Plotting the logarithm (base 10) of the number of surviving individuals against age, from birth to the maximum age reached by any individual, produces a survivorship curve. FIGURE 53-8 shows the three main survivorship curves that ecologists recognize.
In Type I survivorship, the young and those at reproductive age have a high probability of surviving. The probability of survival decreases more rapidly with increasing age; mortality is concentrated later in life.
In Type III survivorship, the probability of mortality is greatest early in life, and those individuals that avoid early death subsquently have a high probability of survival, that is, the probability of survival increases with increasing age.
In Type II survivorship, which is intermediate between Types I and III, the probability of survival does not change with age. The probability of death is equally likely across all age groups, resulting in a linear decline in survivorship. This constancy probably results from essentially random events that cause death with little age bias. Although this relationship between age and survivorship is rare.
metapopulation
A population that is divided into several local populations among which individuals occasionally disperse (emigrate and immigrate).
source habitats
Good habitats, called source habitats, are areas where local reproductive success is greater than local mortality.
Source populations
Source populations generally have greater population densities than populations at less suitable sites, and surplus individuals in the source habitat disperse and find another habitat in which to settle and reproduce.
sink habitats
Individuals living in lower quality habitats may suffer death or, if they survive, poor reproductive success. Lower quality habitats, called sink habitats, are areas where local reproductive success is less than local mortality
sink population
Without immigration from other areas, a sink population declines until extinction occurs. If a local population becomes extinct, individuals from a source habitat may recolonize the vacant habitat at a later time. Source and sink habitats, then, are linked to one another by dispersal.
Human population
characteristic J curve of exponential population growth shown in Figure 53-13 reflects the decreasing amount of time it has taken to add each additional billion people to our numbers.
Thomas Malthus (1766–1834), a British clergyman and economist, was one of the first to recognize that the human population cannot continue to increase indefinitely. He maintained that the inevitable consequences of population growth are famine, disease, and war.
zero population growth, the point at which the birth rate equals the death rate (r = 0), will occur toward the end of the 21st century.
Human demographics
the science that deals with human population statistics such as size, density, and distribution, provides information on the populations of various countries. As you probably know, not all parts of the world have the same rates of population increase. Countries can be classified into two groups, highly developed and developing, based on their rates of population growth, degrees of industrialization, and relative prosperity
Highly developed countries,
such as the United States, Canada, France, Germany, Sweden, Australia, and Japan, have low rates of population growth and are highly industrialized relative to the rest of the world. have the lowest birth rates in the world. Indeed, some highly developed countries such as Germany have birth rates just below that needed to sustain the population and are thus declining slightly in numbers. Highly developed countries also have low infant mortality rates. longer life expectancies
Developing countries
fall into two subcategories: moderately developed and less developed. Mexico, Turkey, Thailand, and most countries of South America are examples of moderately developed countries. Their birth rates and infant mortality rates are generally higher than those of highly developed countries, but the rates are declining. Moderately developed countries have a medium level of industrialization.
Bangladesh, Niger, Ethiopia, Laos, and Cambodia are examples of less developed countries. These countries have the highest birth rates, the highest infant mortality rates, the lowest life expectancies.
doubling time
the amount of time it would take for its population to double in size, assuming its current growth rate did not change.
replacement-levelfertility
the number of children a couple must produce to “replace” themselves.
total fertility rate
the average number of children born to a woman during her lifetime
age structure
To predict the future growth of a population, it is important to know its age structure, which is the number and proportion of people at each age in a population. The number of males and number of females at each age, from birth to death, are represented in an age structure diagram.
The overall shape of an age structure diagram indicates whether the population is increasing, stationary, or shrinking. The age structure diagram for less developed countries is shaped like a pyramid. Because the largest percentage of the population is in the prereproductive age group (that is, 0 to 14 years of age), the probability of future population growth is great.
population growth momentum
A strong population growth momentum exists because when all these children mature they will become the parents of the next generation, and this group of parents will be larger than the previous group. Thus, even if the fertility rates in these countries decline to replacement level (that is, couples have smaller families than their parents did), the population will continue to grow for some time. Population growth momentum can have either a positive value (that is, the population will grow) or a negative value (that is, the population will decline). However, it is usually discussed in a positive context, to explain how the future growth of a population is affected by its present age distribution.
People overpopulation
occurs when the environment is worsening from too many people, even if those people consume few resources per person.
current problem in many developing nations.
consumption overpopulation
occurs when each individual in a population consumes too large a share of resources. The effect of consumption overpopulation on the environment is the same as that of people overpopulation—pollution and degradation of the environment.
Most affluent highly developed nations, including the United States, suffer from consumption overpopulation.
Highly developed nations represent about 18% of the world’s population, yet they consume significantly more than half its resources.
These nations also generate 75% of the world’s pollution and waste.
According to the Worldwatch Institute, a private research institution in Washington, D.C., highly developed nations account for the lion’s share of total resources consumed, as follows: 86% of aluminum used, 76% of timber harvested, 68% of energy produced, 61% of meat eaten, and 42% of fresh water consumed.
community
consists of an association of populations of different species that live and interact in the same place at the same time.
Communities exhibit characteristic properties that populations lack. These properties, known collectively as community structure and community functioning, include the number and types of species present, the relative abundance of each species, the interactions among different species, community resilience to disturbances, energy and nutrient flow throughout the community, and productivity.
ecosystem
A biological community and its abiotic environment together compose an ecosystem.
Community ecology
the description and analysis of patterns and processes within the community. Finding common patterns and processes in a wide variety of communities helps ecologists understand community structure and functioning.
facilitation
Certain species interact in positive ways, in a process known as facilitation, which modifies and enhances the local environment for other species. For example, alpine plants in harsh mountain environments grow faster and larger and reproduce more successfully when certain other plants are growing nearby.
Also, each organism plays one of three main roles in community life: producer, consumer, or decomposer.
Unraveling the many positive and negative, direct and indirect interactions of organisms living together as a community is one of the goals of community ecologists.
ecological niche
Every species is thought to have its own ecological role within the structure and function of a community; we call this role its ecological niche.
includes the local environment in which a species lives—its habitat. A niche also encompasses what a species eats, what eats it, what organisms it competes with, and how it interacts with and is influenced by the abiotic components of its environment, such as light, temperature, and moisture. The niche thus represents the totality of adaptations by a species to its environment, its use of resources, and the lifestyle to which it is suited. Although a complete description of an organism’s ecological niche involves many dimensions and is difficult to define precisely, ecologists usually confine their studies to one or a few niche variables, such as feeding behaviors or ability to tolerate temperature extremes.
fundamental niche
The potential ecological niche of a species is its fundamental niche, but various factors, such as competition with other species, may exclude it from part of this fundamental niche.
realized niche
The lifestyle that a species actually pursues and the resources it actually uses make up its realized niche.
limiting resource
Any environmental resource that, because it is scarce or unfavorable, tends to restrict the ecological niche of a species.
Most of the limiting resources that have been studied are simple variables, such as the soil’s mineral content, temperature extremes, and precipitation amounts.
Fig. 54.4 Abiotic and biotic factors that affect barnacle distribution
(After Connell, J. H. “The Influence of Interspecific Competition and Other Factors on the Distribution of the Barnacle Chthamalus stellatus.” Ecology,
Vol. 42, 1961.)
(a) Species of barnacles belonging to two genera, Chthamalus and Balanus, grow in the intertidal zone of a rocky shore in Scotland.
(b) When Chthamalus individuals were experimentally removed, Balanus individuals did not expand into their section of the rock.
(c) When Balanus individuals were experimentally removed, Chthamalus individuals spread into the empty area.
Competition
occurs when two or more individuals attempt to use the same essential resource, such as food, water, shelter, living space, or sunlight.
Competition occurs among individuals within a population (intraspecific competition) or between different species (interspecific competition).
competitive exclusion principle
hypothesized that one species excludes another from its niche as a result of interspecific competition. Although it is possible for species to compete for some necessary resource without being total competitors, two species with abso- lutely identical ecological niches cannot coexist. Coexistence oc- curs, however, if the overlap between the two niches is reduced.
resource partitioning
Reduced competition among coexisting species as a result of each species’ niche differing from the others in one or more ways.
Resource partitioning may also include timing of feeding, location of feeding, nest sites, and other aspects of a species’ ecological niche.
Difference in root depth is an example of resource partitioning in plants.
character displacement
Sometimes populations of two similar species occur together in some locations and separately in others. Where their geographic distributions overlap, the two species tend to differ more in their structural, ecological, and behavioral characteristics than they do where each occurs in separate geographic areas. Such divergence in traits in two similar species living in the same geographic area is known as character displacement.
There are several well-documented examples of character displacement between two closely related species. The flowers of two Solanum species in Mexico are quite similar in areas where either one or the other occurs. However, where their distributions overlap, the two species differ significantly in flower size and are pollinated by different kinds of bees. In other words, character displacement reduces interspecific competition, in this case for the same animal pollinator.
bill sizes of Darwin’s finches provide another example of character displacement. On large islands in the Galápagos where the medium ground finch (Geospiza fortis) and the small ground finch (G. fuliginosa) occur together, their bill depths are distinctive. Geospiza fuliginosa has a smaller bill depth that en- ables it to crack small seeds, whereas G. fortis has a larger bill depth that enables it to crack medium-sized seeds. However, G. fortis and G. fuliginosa also live on separate islands. Where the two species live separately, bill depths are about the same intermediate size, perhaps because there is no competition from the other species.
Predation
the consumption of one species, the prey, by another, the predator
coevolution
The reciprocal adaptation of two or more species that occurs as a result of their close interactions over a long period.
aposematic coloration
Conspicuous colors or patterns, which advertise a species’ unpalatability to potential predators, are known as aposematic coloration (pronounced “ap′-uh-suh-mat′-ik”; from the Greek apo, “away,” and semat, “a mark or sign”), or warning coloration.
Ecological Interactions among Species
cryptic coloration
colors or markings that help them hide from predators by blending into their physical surroundings.
Batesian mimicry
Sometimes a defenseless species (a mimic) is protected from predation by its resemblance to a species that is dangerous in some way (a model). Such a strategy is known as Batesian mimicry.
For example, a harmless scarlet king snake looks so much like a venomous coral snake that predators may avoid it. Interestingly, the range of the scarlet king snake extends far beyond that of the coral snake. In an area where coral snakes do not occur, having the coloration of the model confers no special advantage to the king snake and may be harmful, triggering natural selection. This seems to be the case: in 2008 scientists reported in the journal Nature that scarlet king snake populations located far from coral snakes have undergone natural selection and look less like their model.
Müllerian mimicry
different species (co-models), all of which are poisonous, harmful, or distasteful, resemble one another. Although their harmfulness protects them as individual species, their similarity in appearance works as an added advantage because potential predators more easily learn a single common aposematic coloration. Scientists hypothesize that viceroy and monarch butterflies are an example of Müllerian mimicry.
Symbiosis
any intimate relationship or association between members of two or more species.
symbionts
the partners of a symbiotic relationship, called symbionts, may benefit from, be unaffected by, or be harmed by the relationship.
Mutualism
a symbiotic relationship in which both partners benefit. Mutualism is either obligate (essential for the survival of both species) or facultative (either partner can live alone under certain conditions).
Commensalism
a type of symbiosis in which one species benefits and the other one is neither harmed nor helped.
Parasitism
a symbiotic relationship in which one member, the parasite, benefits, whereas the other, the host, is adversely affected. The parasite obtains nourishment from its host. A parasite rarely kills its host directly but may weaken it, rendering it more vulnerable to predators, competitors, or abiotic stressors. When a parasite causes disease and sometimes the death of a host, it is called a pathogen.
ectoparasites
Ticks and other parasites that live outside the host’s body.
endoparasites
Parasites such as tapeworms that live within the host.
keystone species
are crucial in determining the nature of the entire community, that is, its species composition and ecosystem functioning.
usually not the most abundant species in the community. Although present in relatively small numbers, the individuals of a keystone species profoundly influence the entire community because they often affect the amount of available food, water, or some other resource. Thus, the impact of keystone species is greatly disproportionate to their abundance. If a keystone species disappears from a community, many other spe- cies in that community may become more common or rarer, or may even disappear.
The term keystone species was coined by ecologist Robert T. Paine in 1969, based on his experimental studies along the Pacific coast in the state of Washington (FIG. 54-15). Paine removed a predatory sea star, Pisaster ochraceus, from a rocky intertidal community that included barnacles, mussels, limpets, and chitons, all of which the sea star preyed on.Paine noted that when a keystone predator such as the sea star is removed from a community, the species diversity of that community changes dramatically.
One problem with the concept of keystone species is that it is often difficult to measure all the direct and indirect impacts of a keystone species on an ecosystem.
dominant species
greatly affect the community because they are very common. Trees, the dominant species of forests, change the local environment.
Typically, a community has one or a few dominant species, and most other species are relatively rare.
Bottom-up processes
Bottom-up processes are based on food webs, the interconnected series of organisms through which energy flows in an ecosystem. Food webs always have plants or other producers at the first (lowest) trophic level.
top-down processes
regulate ecosystem function by trophic interactions, particularly from the highest trophic level.
If top-down processes dominate an ecosystem, the effects of an increase in the population of top predators cascade down the food web through the herbivores and producers. In fact, top-down processes are also known as a trophic cascade.
Species diversity
a measure of both the number of species within a community (species richness) and the relative importance of each species, based on its abundance, productivity, or size (species evenness).
Ecologists have developed various mathematical expressions, such as the Shannon index, to represent species diversity quantitatively. These diversity indices enable ecologists to compare species diversity in different communities.
Species richness
the number of species in a community, is determined by counting the species of interest. Tropical rain forests and coral reefs are examples of communities with extremely high species richness. In contrast, geographically isolated islands and mountaintops exhibit low species richness.
Species evenness
tells us about the relative abundance of one species compared to other species.
ecotone
Species richness is usually greater at the margins of distinct communities than in their centers. The reason is that an ecotone, a transitional zone where two or more communities meet, contains all or most of the ecological niches of the adjacent communities as well as some that are unique to the ecotone. This change in species composition produced at ecotones is known as the edge effect.
disturbance
any event in time that disrupts community or population structure.
succession
The process of community development over time, which involves species in one stage being replaced by different species, is called succession. An area is initially colonized by certain early successional species that give way over time to others, which in turn give way much later to late-successional species.
Ecologists distinguish between two types of succession, primary and secondary.
Primary succession
the change in species composition over time in a habitat that was not previously inhabited by organisms. No soil exists when primary succession begins. Bare rock surfaces, such as recently formed volcanic lava and rock scraped clean by glaciers, are examples of sites where primary succession might take place.
Secondary succession
the change in species composition that takes place after some disturbance removes the existing vegetation; soil is already present at these sites. Abandoned agricultural fields or open areas produced by forest fires are common examples of sites where secondary succession occurs.
intermediate disturbance hypothesis
by Joseph H. Connell.
he proposed that species richness is greatest at moderate levels of disturbance
One of the difficulties with the intermediate disturbance hypothesis is defining precisely what constitutes an “intermediate” level of disturbance.
organismic model
U.S. botanist Frederick E. Clements’s view was that a community went through certain stages of development, like the embryonic stages of an organism, and eventually reached n adult state; the developmental process was succession, and the adult state was the climax community. This cooperative view of the community, called the organismic model, stresses the interaction of the members, which tend to cluster in tightly knit groups within discrete community boundaries,
individualistic model
U.S. ecologist Henry A. Gleason, held that biological interactions are less important in the production of communities than are environmental gradients (such as climate and soil) or even chance. Indeed, the concept of a community is questionable. It may be a classification category with no reality, reflecting little more than the tendency of organisms with similar environmental requirements to live in similar places. This school of thought, called the individualistic model, emphasizes species individuality, with each species having its own particular abiotic living requirements. It holds that communities are therefore not interdependent associations of organisms. Rather, each species is independently distributed across a continuum of areas that meets its own individual requirements.
food web
A complex interconnection of all the food chains in an ecosystem.
food chain
The series of organisms through which energy flows in an ecosystem. Each organism in the series eats or decomposes the preceding organism in the chain.
Ecosystems
Individual communities and their abiotic environments are ecosystems, which are the basic units of ecology.
Ecosystem ecology
a subfield of ecology that studies energy flow and the cycling of chemicals among the interacting biotic and abiotic parts of an ecosystem.
energy flow
The passage of energy in a one-way direction through an ecosystem.
Primary producers
also called autotrophs, or simply, producers, form the beginning of the food chain by capturing the sun’s energy through photosynthesis. Producers, by incorporating the chemicals they manufacture into their own biomass (living material), become potential food resources for other organisms. Plants are the most significant producers on land, whereas algae and cyanobacteria are important producers in aquatic environments.
consumers
All other organisms in a community are consumers, also called heterotrophs, that extract energy from organic molecules produced by other organisms. Herbivores
are consumers that eat plants, from
which they obtain the chemical energy of the producers’ molecules and the building materials used to
construct their own tissues. Herbivores are, in turn, consumed by carnivores, consumers that reap
the energy stored in the herbivores’
molecules. Other consumers, called
omnivores, eat a variety of organisms, both plant and animal.
detritus feeders
Some consumers, called detritus feeders, or detritivores, eat detritus, which is dead organic matter that includes animal carcasses, leaf litter, and feces. Detritus feeders and microbial decomposers destroy dead organisms and waste products. Decomposers, also called saprotrophs, include microbial heterotrophs that supply themselves with energy by breaking down organic molecules in the remains (carcasses and body wastes) of all members of the food chain. They typically release simple inorganic molecules, such as carbon dioxide and mineral salts, which may be reused by producers. Most bacteria and fungi are important decomposers.
trophic levels
Food webs are divided into trophic levels (from the Greek tropho, which means “nourishment”). Producers (organisms that photosynthesize) occupy the first trophic level, primary consumers (herbivores) occupy the second, secondary consumers (carnivores and omnivores) the third, and so on.
ecological pyramids
Ecologists sometimes compare trophic levels by determining the number of organisms, the biomass, or the relative energy found at each level. This information is presented graphically as ecological pyramids. The base of each ecological pyramid represents the producers, the next level is the primary consumers (herbivores), the level above that is the secondary consumers (carnivores), and so on. The relative area of each bar of the pyramid is proportional to what is being demonstrated.
pyramid of numbers
shows the number of organisms at each trophic level in a given ecosystem, with a larger area illustrating greater numbers for that section of the pyramid. In most pyramids of numbers, fewer organisms occupy each successive trophic level. Thus, in African grasslands the number of herbivores, such as zebras and wildebeests, is greater than the number of carnivores, such as lions. Inverted pyramids of numbers, in which higher trophic levels have more organisms than lower trophic levels, are often observed among decomposers, parasites, and herbivorous insects. One tree provides food for thousands of leaf-eating insects, for example.
are of limited usefulness because they do not indicate the biomass of the organisms at each level and they do not indicate the amount of energy transferred from one level to another.
A pyramid of biomass
illustrates the total biomass at each successive trophic level.
Biomass
a quantitative estimate of the total mass, or amount, of living material; it indicates the amount of fixed energy at a particular time. Units of measure vary: biomass may be represented as total volume, dry weight, or live weight.
The 90% reduction in biomass is an approximation; actual biomass reduction from one trophic level to the next varies widely. From this brief exercise, you see that although carnivores do not eat producers, a large producer biomass is required to support carnivores in a food web.
A pyramid of energy
indicates the energy content, often expressed as kilocalories per square meter per year, of the biomass of each trophic level. A common method ecologists use to measure energy content is to burn a sample of tissue in a calorimeter; the heat released during combustion is measured to determine the energy content of the organic material in the sample. The second law of thermodynamics explains why there are few trophic levels: energy pyramids are short because of the dramatic reduction in energy content that occurs at each successive trophic level.
gross primary productivity (GPP)
gross primary productivity (GPP) of an ecosystem is the rate at which energy is captured during photosynthesis. Thus, GPP is the total amount of photosynthetic energy captured in a given period.
net primary productivity (NPP)
Energy that remains in plant tissues after cellular respiration has occurred is called net primary productivity (NPP). That is, NPP is the amount of biomass (the energy stored in plant tissues) found in excess of that broken down by a plant’s cellular respiration for normal daily activities. NPP represents the rate at which this organic matter is actually incorporated into plant tissues to produce growth.
secondary productivity
he remaining energy—less than 20%—is avail- able to produce new biomass, that is, new tissues. This net energy available for biomass production by consumer organisms is called secondary productivity. An ecosystem’s secondary productivity is based on its primary productivity.
persistence
The persistence of synthetic pesticides and industrial chemicals is a result of their novel chemical structures. These toxins accumulate in the environment because ways to degrade them have not evolved in natural decomposers such as bacteria.
bioaccumulation
When an organism does not metabolize (break down) or excrete a persistent toxin, the toxin simply gets stored, usually in fatty tissues. Over time, the organism may accumulate high concentrations of the toxin. The buildup of such a toxin in an organism’s body is known as bioaccumulation.
biological magnification
Organisms at higher trophic levels in food webs tend to store greater concentrations of bioaccumulated toxins in their bodies than do those at lower levels. The increase in concentration as the toxin passes through successive levels of the food web is known as biological magnification.
biogeochemical cycles
Matter moves in numerous cycles from one part of an ecosystem to another—that is, from one organism to another (in food chains) and from living organisms to the abiotic environment and back again. We call these cycles of matter biogeochemical cycles because they involve biological, geologic, and chemical interactions.
the carbon cycle
The global movement of carbon between the abiotic environment, including the atmosphere and ocean, and organisms is known as the carbon cycle.
fossil fuels
Coal, oil, and natural gas, called fossil fuels because they formed from the remains of ancient organisms, are vast deposits of carbon compounds, the end products of photosynthesis that occurred millions of years ago.
nitrogen cycle
in which nitrogen cycles between the abiotic environment and organisms, has five steps: nitrogen fixation, nitrification, assimilation, ammonification, and denitrification. Bacteria are exclusively involved in all these steps except assimilation.
nitrogen fixation
The first step in the nitrogen cycle, biological nitrogen fixation involves conversion of gaseous nitrogen (N2) to ammonia (NH3). This process fixes nitrogen into a form that organisms can use. Combustion, volcanic action, lightning discharges, and industrial processes also fix nitrogen as nitrate (NO3−). Nitrogen-fixing bacteria, including cyanobacteria and certain other freeliving and symbiotic bacteria, carry on biological nitrogen fixation in soil and aquatic environments. Nitrogen-fixing bacteria employ an enzyme called nitrogenase to break up molecular nitrogen and combine the resulting nitrogen atoms with hydrogen.
heterocysts
Filamentous cyanobacteria have special oxygen- excluding cells called heterocysts that function to fix nitrogen.
nitrification
The second step of the nitrogen cycle is nitrification, the conversion of ammonia (NH3) or ammonium (NH4+), formed when water reacts with ammonia, to nitrate (NO3−). Soil bacteria are responsible for the two-phase process of nitrification, which furnishes these bacteria, called nitrifying bacteria, with energy.
assimilation
In the third step, assimilation, roots absorb ammonia (NH3), ammonium (NH4+), or nitrate (NO3−) formed by nitrogen fixation and nitrification, and incorporate the nitrogen into proteins, nucleic acids, and chlorophyll.
ammonification
The fourth step, ammonification, is the conversion of organic nitrogen compounds into ammonia (NH3) and ammonium ions (NH4+). Ammonification begins when organisms produce 4 nitrogen-containing wastes such as urea in urine and uric acid in the wastes of birds. As these substances, along with the nitrogen compounds in dead organisms, decompose, nitrogen is released into the abiotic environment as ammonia (NH3). The bacteria that perform ammonification in both the soil and aquatic environments are called ammonifying bacteria. Most available nitrogen in the soil derives from the recycling of organic nitrogen by ammonification.
denitrification
The fifth step of the nitrogen cycle is denitrification, the reduction of nitrate (NO3−) to gaseous nitrogen (N2). Denitrifying bacteria reverse the action of nitrogen-fixing and nitrifying bacteria by returning nitrogen to the atmosphere as nitrogen gas.
Dentrifying bacteria are anaerobic and therefore live and grow best where there is little or no free oxygen. For example, they are found deep in the soil near the water table, an environment that is nearly oxygen-free.
nitrogen oxides
the high temperature of combustion converts some atmospheric nitrogen to nitrogen oxides. Automobile exhaust is one of the main sources of nitrogen oxides.
photochemical smog
Nitrogen oxides are a necessary ingredient in the production of photochemical smog, a mixture of several air pollutants that injure plant tissues, irritate eyes, and cause respiratory problems in humans.
acid deposition
Nitrogen oxides also react with water in the atmosphere to form nitric acid (HNO3) and nitrous acid (HNO2). When these and other acids leave the atmosphere as acid deposition, they decrease the pH of surface waters (lakes and streams) and soils. Acid deposition has been linked to declining animal populations in aquatic ecosystems. On land, acid deposition alters soil chemistry: certain essential minerals, such as calcium and potassium, wash out of the soil and are therefore unavailable for plants. Nitrous oxide (N2O), one of the nitrogen oxides, retains heat in the atmosphere (like CO2) and so promotes global climate change.
phosphorus cycle
Phosphorus does not exist in a gaseous state and therefore does not enter the atmosphere. In the phosphorus cycle, phosphorus cycles from the land to sediments in the ocean and back to the land.
As water runs over rocks containing phosphorus, it gradually erodes the surface and carries off inorganic phosphate (PO43−). The erosion of phosphorus rocks releases phosphate into the soil, where it is taken up by roots in the form of inorganic phosphates. Once in cells, phosphates are incorporated into a variety of biological molecules, including nucleic acids, ATP, and the phospholipids that make up cell membranes. Animals obtain most of their required phosphorus from the food they eat, although in some places drinking water may contain a substantial amount of inorganic phosphate. Phosphate released by decomposers becomes part of the pool of inorganic phosphate in the soil that plants reuse. Thus, like carbon and nitrogen, phosphorus moves through the food web as one organism consumes another.
Dissolved phosphate enters aquatic ecosystems through absorption by algae and aquatic plants, which zooplankton and larger organisms consume. In turn, a variety of fishes and mollusks eat the zooplankton. Ultimately, decomposers break down wastes and dead organisms to release inorganic phosphate into the water, making it available for use again by aquatic producers.
hydrologic cycle
water continuously circulates from the ocean to the atmosphere to the land and back to the ocean. Water moves from the atmosphere to the land and ocean in the form of precipitation (rain, sleet, snow, or hail). Water that evaporates from the ocean surface and from soil, streams, rivers, and lakes eventually condenses and forms clouds in the atmosphere. In addition, transpiration, the loss of water vapor from land plants, adds a considerable amount of water vapor to the at- mosphere. Roughly 97% of the water a plant absorbs from the soil is transported to the leaves, where it is lost by transpiration.
Water may evaporate from land and re-enter the atmosphere directly. Alternatively, it may flow in rivers and streams to coastal estuaries, where fresh water meets the ocean. The movement of surface water from land to ocean is called runoff, and the area of land drained by runoff is called a watershed. Water also percolates (seeps) downward in the soil to become groundwater, where it is trapped and held for a time. The underground caverns and porous layers of rock in which groundwater is stored are called aquifers. Groundwater may reside in the ground for hundreds to many thousands of years, but eventually it supplies water to the soil, streams and rivers, plants, and the ocean. The human removal of more groundwater than precipitation or melting snow recharges, called aquifer depletion, eliminates groundwater as a water resource.
Regardless of its physical form (solid, liquid, or vapor) or location, every molecule of water eventually moves through the hydrologic cycle. As is true of the other cycles, water (in the form of glaciers, polar ice caps, and certain groundwater) can be lost from the cycle for thousands of years.
What does the sun do?
The sun powers the hydrologic cycle, carbon cycle, and other biogeochemical cycles and is the primary determinant of climate. Without the sun, almost all life on Earth would cease.
the Coriolis effect
Earth’s rotation influences the direction that wind blows. Because Earth rotates from west to east, wind swerves to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This tendency of moving air to be deflected from its path by Earth’s rotation is known as the Coriolis effect.
ocean currents
The persistent prevailing winds blowing over the ocean produce mass movements of surface ocean water known as ocean currents. The prevailing winds generate circular ocean currents called gyres. For example, in the North Atlantic, the tropical trade winds tend to blow toward the west, whereas the westerlies in the midlatitudes blow toward the east. This helps establish a clockwise gyre in the North Atlantic. Thus, surface ocean currents and winds tend to move in the same direction, although there are many variations on this general rule.
The Coriolis effect is partly responsible for the paths that surface ocean currents travel. Earth’s rotation from west to east causes surface ocean currents to swerve to the right in the Northern Hemisphere, producing a clockwise gyre of water currents. In the Southern Hemisphere, ocean currents swerve to the left, producing a counterclockwise gyre.
El Niño–Southern Oscillation (ENSO
ENSO is a periodic warming of surface waters of the tropical eastern Pacific that alters both oceanic and atmospheric circulation patterns and results in unusual weather in areas far from the tropical Pacific.
The warmer sea-surface temperatures and accompanying changes in ocean circulation patterns off the west coast of South America prevent colder, nutrient-laden deeper waters from upwelling (coming to the surface). The lack of nutrients in the water results in a severe decrease in the populations of anchovies and many other marine fishes. Other species, such as shrimp and scallops, thrive during an ENSO event.
Climate
the average weather conditions, plus extremes (records), that occur in a given place over a period of years. The two most important factors that determine an area’s climate are temperature (both average temperature and temperature extremes) and precipitation (both average precipitation and seasonal distribution). Other climate factors include wind, humidity, fog, cloud cover, and lightning-caused wildfires. Unlike weather, which changes rapidly, climate generally changes slowly, over hundreds or thousands of years.
The wide variety of organisms on Earth evolved in part because of the many different climates, ranging from cold, snow-covered, polar climates to hot, tropical climates where it rains almost every day.
rain shadows
As the air mass moves down on the other side of the mountain, it is warmed and clouds evaporate, thereby lessening the chance of precipitation of any remaining moisture. This situation exists on the west coast of North America, where precipitation falls on the western slopes of mountains that are close to the coast. The dry lands on the sides of the mountains away from the prevailing wind (in this case, east of the mountain range) are called rain shadows.
A rain shadow is the arid or semiarid land that occurs on the leeward side of a mountain.
microclimates
Differences in elevation, in the steepness and direction of slopes, and therefore in exposure to sunlight and prevailing winds may produce local variations in climate known as microclimates, which are sometimes quite different from their overall surroundings.
deforestation
the clearance of large expanses of forest for agriculture or other uses. When a forest is removed, the total amount of water and minerals that flow into streams increases drastically.
Ecosystem management
a conservation approach that emphasizes restoring and maintaining the quality of an entire ecosystem rather than the conservation of individual species.
biome
a large, relatively distinct terrestrial region that has similar climate, soil, plants, and animals regardless of where it occurs. Because it covers such a large geographic area, a biome encompasses many interacting landscapes.
Tundra
(also called arctic tundra) occurs in extreme northern latitudes wherever snow melts seasonally.
long, harsh winters and extremely short summers.
soils tend to be geologically young. These soils are usually nutrient poor and have little organic litter in the uppermost layer of soil. Although the soil surface melts during the summer, tundra has a layer of permanently frozen ground called permafrost that varies in depth and thickness. Because permafrost interferes with drainage, the thawed upper zone of soil is usually waterlogged during the summer. Limited precipitation, combined with low temperatures, flat topography (surface features), and permafrost, produces a landscape of broad, shallow lakes, sluggish streams, and boggy plains covered by lichens and small plants.
Low species richness and low primary productivity
regenerates quite slowly after it has been disturbed. Long-lasting injury, likely to persist for hundreds of years, has been done to large portions of the arctic tundra as a result of oil exploration and military use.
alpine tundra
A similar ecosystem located in the higher elevations of mountains, above the tree line, is called alpine tundra to distinguish it from arctic tundra.
An ecosystem located in the higher elevations of
mountains, above the treel ine and below the snow line.
boreal forest
south of the tundra** (**or taiga), which stretches across both North America and Eurasia. world’s largest biome. Winters are extremely cold and severe, although not as harsh as in the tundra. receives little precipitation and its soil is typically acidic, is low in minerals, and has a deep layer of partly decomposed conifer needles at the surface. contains numerous ponds and lakes in water-filled depressions that grinding ice sheets dug during the last Ice Age.
Black and white spruces, balsam fir, eastern larch, and other conifers dominate the boreal forest, but deciduous trees such as aspen or birch, which shed their leaves in autumn, form striking stands.
Animal life includes some larger species. However, most animal life is medium-sized to small. Most species of birds are seasonally abundant but migrate to warmer climates for winter. Insects are numerous, but there are few amphibians and reptiles except in the southern boreal forest.
Most not suitable for agriculture because of its short growing season and mineral-poor soil. Harvested primarily by clear-cutting, is currently the primary source of the world’s industrial wood and wood fiber.
temperate rain forest
A coniferous biome characterized by cool weather, dense fog, and high precipitation, e.g., the north Pacific coast of North America. Winters are mild, and summers are cool. Relatively nutrient-poor soil, although its organic content may be high. Cool temperatures slow the activity of bacterial and fungal decomposers. Thus, needles and large fallen branches and trunks accumulate on the ground as litter that takes many years to decay and release inorganic minerals to the soil.
The dominant vegetation type in the North American temperate rain forest is large evergreen trees, rich in epiphytic vegetation, which consists of smaller plants that grow nonparasitically on the trunks and branches of large trees. Squirrels, wood rats, mule deer, elk, numerous bird species (such as jays, nuthatches, and chickadees), several species of reptiles (such as painted turtles and western terrestrial garter snakes), and amphibians (such as Pacific giant salamanders and Pacific treefrogs) are common temperate rainforest animals.
one of the richest wood producers in the world, supplies us with lumber and pulpwood. It is also one of the most complex ecosystems in terms of species richness.
temperate deciduous forest
Seasonality (hot summers and cold winters) is characteristic, which occurs in temperate areas where precipitation ranges from about 75 to 126 cm (30 to 50 in) annually. Typically, the soil consists of both a topsoil rich in organic material and a deep, clay-rich lower layer.
Broad-leaf hardwood trees that lose their foliage annually dominate the northeastern and Mid-Atlantic United States. The trees form a dense canopy that overlies saplings and shrubs.
Originally contained a variety of large mammals now regionally extinct, plus deer, bears, and many small mammals and birds. Both reptiles and amphibians abounded, together with a denser and more varied insect life than exists today.
In Europe and North America, logging and land clearing for farms, tree plantations, and cities have removed much of the original temperate deciduous forest. Where it has regenerated, temperate deciduous forest is often in a semi-natural state—that is, highly modified by humans for recreation, livestock foraging, timber harvest, and other uses. Although these returning forests do not have the biological diversity of virgin stands, many forest organisms have successfully become re-established.
temperate grasslands
Summers are hot, winters are cold, fires help shape the landscape, and rainfall is often uncertain. Annual precipitation averages 25 to 75 cm. Grassland soil contains considerable organic material because surface parts of many grasses die off each winter and contribute to the organic content of the soil (the roots and rhizomes survive underground).
Chaparral
Some hilly temperate environments have mild winters with abundant rainfall, combined with extremely dry summers. This vegetation type is also known as maquis in the Mediterranean region, mallee scrub in Australia, matorral in Chile, and Cape scrub in Africa. Soil is thin and infertile. Frequent fires occur naturally in this environment, particularly in late summer and autumn.
A dense growth of evergreen shrubs, often of drought-resistant pine or scrub oak trees, dominates. During the rainy winter season the landscape may be lush and green, but during the hot, dry summer the plants lie dormant. Trees and shrubs often have hard, small, leathery leaves that resist water loss. Many plants are also fire-adapted and grow best in the months following a fire. Such growth is possible because fire releases minerals that were tied up in the plants that burned. Denser, thicker vegetation tends to accumulate when periodic fires are prevented; then, when a fire does occur, it is much more severe.
Deserts
Dry areas found in temperate (cold deserts) and subtropical or tropical regions (warm deserts). North America has four distinct deserts. The low water-vapor content of the desert atmosphere leads to daily temperature extremes of heat and cold, so a major change in temperature occurs in each 24-hour period. Deserts vary greatly depending on the amount of precipitation they receive, which is generally less than 25 cm (10 in) per year. A few deserts are so dry that virtually no plant life occurs in them. As a result of sparse vegetation, desert soil is low in organic material but often high in mineral content. Desert plants tend to have reduced leaves or no leaves, an adaptation that conserves water.
Humans have altered North American deserts in several ways. Off-road vehicles damage desert vegetation, which sometimes takes years to recover. When the top layer of desert soil is disturbed, erosion occurs more readily, and less vegetation grows to support native animals. caused groundwater levels to drop. Aquifer depletion in U.S. deserts is particularly critical in southern Arizona and southwestern New Mexico.
savanna
a tropical grassland with widely scattered clumps of low trees. Found in areas of relatively low or seasonal rainfall with prolonged dry periods. precipitation regulates seasons. Annual precipitation is 85 to 150 cm (34 to 60 in). soil is low in essential minerals, in part because it is strongly leached. Often rich in aluminum, which resists leaching, and in places the aluminum reaches levels that are toxic to many plants. Wide expanses of grasses interrupted by occasional trees.
In some places severe overgrazing by domestic animals has contributed to the conversion of marginal savanna into desert, a process known as **desertification, **the reduced grass cover caused by overgrazing allows wind and water to erode the soil; erosion removes the topsoil and decreases the soil’s ability to support crops or livestock.
Tropical dry forests
occur in regions with a wet season and a dry season (usually two to three months each year). Annual precipitation is 150 to 200 cm (60 to 80 in). During the dry season, many tropical trees shed their leaves and remain dormant, much as temperate trees do during the winter. India, Brazil, Thailand, and Mexico are some of the countries that have tropical dry forests. Tropical dry forests intergrade with savanna on their dry edges and with tropical rain forests on their wet edges.
tropical rain forests
The annual precipitatio is 200 to 450 cm (80 to 180 in). Much of this precipitation, which occurs almost daily, comes from locally recycled water that enters the atmosphere by transpiration from the forest’s own trees. often located in areas with ancient, highly weathered, mineral-poor soil. Because temperatures are high and soil moisture is abundant year-round, decay organisms and detritus-feeding ants and termites decompose organic litter quite rapidly.
Very productive despite the scarcity of minerals in the soil. Its plants, stimulated by abundant solar energy and precipitation, capture considerable energy by photosynthesis. Unrivaled in species richness. Tropical rainforest trees support extensive epiphytic commu- nities of smaller plants such as orchids and bromeliads. Although epiphytes grow in crotches of branches, on bark, or even on the leaves of their hosts, most use their host trees only for physical sup- port, not for nourishment.
Because little light penetrates to the understory, many plants living there are adapted to climb already-established host trees. Not counting bacteria and other soil-dwelling organisms, about 90% of tropical rainforest organisms live in the middle and upper canopies.
Salinity
the concentration of dissolved salts in a body of water, affects the kinds of organisms present in aquatic ecosystems, as does the amount of dissolved oxygen.
Plankton
usually small or microscopic organisms that are relatively feeble swimmers. For the most part, they are carried about at the mercy of currents and waves. They are unable to swim far horizontally, but some species are capable of large vertical migrations and are found at different depths of water at different times of the day or at different seasons. Plankton are generally subdivided into two major categories: phytoplankton and zooplankton.
Phytoplankton
(photosynthetic cyanobacteria and free-floating algae) are producers that form the base of most aquatic food webs.
Zooplankton
nonphotosynthetic organisms that include protozoa, tiny crustaceans, and the larval stages of many animals.
Nekton
larger, actively swimming organisms such as fishes, turtles, and whales.
Benthos
bottom-dwelling or- ganisms that fix themselves to one spot (sponges, oysters, and bar- nacles), burrow into the sand (many worms and echinoderms), or walk or swim about on the bottom (crayfish, aquatic insect larvae, and brittle stars).
flowing-water ecosystem
The nature of a flowing-water ecosystem changes greatly from its source (where it begins) to its mouth (where it empties into another body of water). Headwater streams (small streams that are the sources of a river) are usually shallow, clear, cold, swiftly flowing, and highly oxygenated. In contrast, rivers downstream from the headwaters are wider and deeper, cloudy (that is, they contain suspended particulates), not as cold, slower flowing, and less oxygenated. Along parts of a stream or river, groundwater wells up through sediments on the bottom; this local input of water moderates the water temperature so that summer temperatures are cooler and winter temperatures are warmer than in adjacent parts of the flowing-water ecosystem.
Streams and rivers depend on land for much of their energy.
standing-water ecosystems
Zonation characterizes standing-water ecosystems. A large lake has three basic zones: the littoral, limnetic, and profundal zones. Smaller lakes and ponds typically lack a profundal zone.
littoral zone
a shallow-water area along the shore of a lake or pond. It includes rooted, emergent vegetation, such as cattails and burreeds, plus several deeper-dwelling aquatic plants and algae. The most productive zone of the lake. Photosynthesis is greatest, in part because light is abundant and because the littoral zone receives nutrient inputs from surrounding land that stimulate the growth of plants and algae. In addition, ponds and lakes—like streams and rivers—depend on detritus carried from the land for much of their energy.
limnetic zone
the open water beyond the littoral zone, that is, away from the shore; it extends down as far as sunlight penetrates to permit photosynthesis. The main organisms of the limnetic zone are microscopic phytoplankton and zooplankton. Larger fishes also spend some of their time in the limnetic zone, although they may visit the littoral zone to feed and reproduce. Because of the depth of this zone, less vegetation grows in the limnetic zone than in the littoral zone.
land areas
Alfred Wallace, who independently discovered the same theory of evolution by natural selection as Charles Darwin, divided Earth’s land areas into six major biogeographic realms: the Palearctic, Nearctic, Neotropical, Ethiopian, Oriental, and Australian. A major barrier separates each of the six biogeographic realms from the others and helps maintain each region’s biological distinctiveness.
The Neotropical realm was almost completely isolated from the Nearctic realm and other landmasses for most of the past 70 million years. During this time, many marsupial species evolved. The isthmus of Panama, which formed a dry-land connection about 3 million years ago, linked North and South America and provided a route for dispersal. Only three species, the opossum, armadillo, and porcupine, are descendants of animals that survived the northward dispersal from South America, but many species, such as the tapir and llama, are descendants of animals that survived the southward dispersal from North America. Competition from these species caused many of South America’s marsupial species to go extinct.
The Sahara Desert separates the Ethiopian realm from other landmasses. The Ethiopian realm contains the most varied vertebrates of all six realms. Some overlap exists between the Ethiopian realm and Oriental realm because a land bridge with a moist climate linked Africa to Asia during the Miocene and Pliocene epochs. The Oriental realm has the fewest endemic species of all the tropical realms.
The Australian realm has not had a land connection with other regions for more than 85 million years. It has no native placental mammals, and marsupials and monotremes, including the duckbilled platypus and the spiny anteater, dominate it. Adaptive radiation of the marsupials during their long period of isolation led to species with ecological niches similar to those of placental mammals of other realms.
biodiversity hotspots
greenhouse effect
Because carbon dioxide and other gases trap the sun’s radiation somewhat like glass does in a greenhouse, the natural trapping of heat in the atmosphere is called the greenhouse effect, and the gases that absorb infrared radiation are known as greenhouse gases. This natural heating of the atmosphere prevents Earth from becoming a frozen planet. However, the additional warming produced when increased levels of gases produced by human activities absorb additional infrared radiation, called the enhanced greenhouse effect, has potentially catastrophic implications.
stratosphere
encircles the planet some 10 to 45 km (6 to 28 miles) above the surface, contains a layer of ozone that shields the surface from much of the ultraviolet radiation from the sun. If ozone disappeared from the stratosphere, Earth would become unlivable for most forms of life.
Both chlorine- and bromine-containing substances catalyze ozone destruction. The primary chemicals responsible for ozone loss in the stratosphere are a group of chlorine compounds called chlorofluorocarbons (CFCs), have been used as propellants in aerosol cans, coolants in air conditioners & refrigerators, foam-blowing agents for insulation & packaging, & solvents & cleaners for the electronics industry. Additional compounds that also attack ozone include halons (found in many fire extinguishers), methyl bromide (a pesticide), methyl chloroform (an industrial solvent), & carbon tetrachloride (used in many industrial processes, including the manufacture of pesticides and dyes).
Male Hormones
Hormones from the hypothalamus, anterior pituitary, and testes regulate male reproduction by negative feedback systems.
vagina
Female Hormones
nerve impulses
Neurons produce and transmit electrical signals called nerve impulses, or action potentials. The neuron is distinguished from all other cells by its long processes (cytoplasmic extensions). Examine the structure of a common type of neuron, the multipolar neuron shown in FIGURE 41-2.
Glial Cell: Astrocyte
Physically support neurons Provide neurons with nutrients
Remove excess K+, which helps regulate composition of extracellular fluid in CNS
Induce blood vessels to form blood–brain barrier
Communicate with one another and with neurons
Induce synapse formation and strengthen activity of synapses
Respond to neurotransmitters and help regulate neurotransmitter reuptake
May be important in memory and learning Guide neurons during embryonic development
Glial cells: Oligodendrocytes
Form myelin sheaths around neurons in CNS
Glial cells: ependymal cells
Line cavities of CNS
Help produce and circulate cerebrospinal fluid May function as neural stem cells
Glial cells: Microglia
Phagocytosis of bacteria and debris
Release signaling molecules that mediate inflammation
Neural signaling across a synapse
Neural signaling along a neuron
Gas exchange in the lungs and tissues;
Note the differences in partial pressures of oxygen and carbon dioxide before and after gases are exchanged in the tissues.
oxygen–hemoglobin dissociation curve
illustrates the relationship between partial pressure of oxygen and percent saturation of hemoglobin. As oxygen concentration increases, there is a progressive increase in the percentage of hemoglobin that is combined with oxygen. The ability of oxygen to combine with hemoglobin and be released from oxyhemoglobin is influenced by several factors in addition to percent O2 saturation. These factors include pH, carbon dioxide concentration, and temperature.
Bohr effect
Displacement of the oxygen–hemoglobin dissociation curve by a change in pH is known as the Bohr effect. Lactic acid released from active muscles also lowers blood pH and has a similar effect on the oxygen–hemoglobin dissociation curve—more oxygen is unloaded and available for muscle contraction.
Section through the human heart showing the valves
Note the right and left atria, which receive blood, and the right and left ventricles, which pump blood into the arteries. Arrows indicate the direction of blood flow.
the AV bundle divides, sending branches into each ventricle. Fibers of the bundle branches divide further, eventually forming small Purkinje fibers. These fibers conduct impulses to the muscle fibers of both ventricles.
SA node –> atrial muscle fibers (atria contract) –> AV node –> AV bundle –> right and left bundle branches –> Purjinje fibers –> conduct impulses to muscle fibers of both ventricles –> ventricles contract
The sinoatrial (SA) node initiates each heartbeat. The action potential spreads through the muscle fibers of the atria, producing atrial contraction. Transmission is briefly delayed at the atrioventricular (AV) node before the action potential spreads through specialized muscle fibers into the ventricles.
The cardiac cycle
The cycle comprises contraction of both atria followed by both ventricles. White arrows indicate the direction of blood flow; dotted lines indicate the change in size as contraction occurs.
Factors that influence the cardiac output
Ch. 44 Most vertebrates other than fishes have a double circuit of blood vessels: (1) the pulmonary circulation connects the heart and lungs; and (2) the systemic circulation connects the heart with all the body tissues.
The right side of the heart receives oxygen-poor blood and pumps it into the pulmonary circulation. The left side of the heart receives oxygen-rich blood from the lungs and pumps it into the systemic circulation
Systemic and pulmonary circulation: In this highly simplified diagram, red represents oxygen-rich blood
and blue represents oxygen-poor blood. Blue screen highlights systemic circulation. Red screen highlights pulmonary circulation
