Ch 53 Flashcards
population
organisms of the same species that exist in a given geographic area at a given time; it’s a population if the organisms in questions could reproduce and make offspring that is capable of reproducing (obviously meaning that they also have to be in the same place at the same time), populations are shaped by the interactions between individuals and their environment, populations have size and geographical boundaries
population ecology
focuses on statistical data and why numbers of organisms in a population change (or don’t change) over a period of time
characteristics of populations
density and dispersion
density (of a population)
measured as the number of individuals per unit area, so: how many in an area?
dispersion (of a population)
is the pattern of spacing among individuals within the geographic boundaries, so: how are they spaced?
how is population measured?
measuring population (size and) density is a difficult task, we can count individuals–not always easy, or we can estimate population numbers by sampling
sampling
counting the number of animals in one region and then multiplying by the number of regions
clumped dispersion
when individuals aggregate in patches
what is dispersion based on?
dispersion is based on resources, such as safety and food
uniform dispersion
when individuals are evenly spaced, the resource being space to rest
random dispersion
the position of each individual is independent of the others
why might plants appear to have a uniform dispersion?
because when you look at plants as a whole they seem to be uniformly dispersed due to the fact that they each need a certain amount of room to grow and sunlight, but you have to look at the plants of only one species, not all plants
What is the equation for growth of a population?
∆N/∆t=B-D, where N=population size, B=the number of births, D=the number of deaths, and t=time; we are most interested in birth and death rates since population sizes can differ; births can be symbolized as bN and deaths as dN, therefore, ∆N/∆t=bN-dN, which can be simplified down to ∆N/∆t=(b-d)N
What is r? What if r is positive? Negative? Zero?
r is the growth rate, r=b-d, if r is positive, the population is growing, if r is negative, the population is declining, and if r is zero, the population is stable, when we use r in the context of the growth equation, it looks like this: ∆N/∆t=rN because as previously stated, r=b-d
What equation would be used if the time interval was very, very short?
dN/dt=rN, this differential equation is really no different from the one above except the time interval is very, very short, instantaneous change
Immigration
immigration occurs when individuals enter a local population from another population
emigration
emigration occurs when individuals leave an area, emigration=exit
How can the growth equation be modified to include immigration and emigration numbers?
r=(b-d)+(i-e)
What are four factors that produce changes in population size?
natality (birth), mortality (death), immigration, and emigration
What is the intrinsic rate of increase (rmax)?
this is the maximum rate at which species or populations can increase under ideal conditions, this means minimizing death and emigration and maximizing birth and immigration; so, it is the maximal growth rate for a population
In regards to the intrinsic rate of increase, what is K?
K is the carrying capacity which is the largest population that can be maintained, K is not a rate, it’s a number
What is exponential population growth? What kind of curve does it have? What about a logistic population curve?
exponential population growth is quick growth, it is shown with a J-shaped curve, a logistic population curve is when there’s a cap that can’t be broken and it is shown with an S-shaped curve
Environmental resistance
there isn’t infinite space or food for a population, so, as the population increases, the environmental resistance increases as well
the logistic equation
a population growth pattern that begins with exponential growth and then slows as the population reaches carrying capacity (K)
What is N?
the number of individuals in a population
exponential growth
a population growth pattern in which the population grows at a constant rate (r), so, for every time interval, a growing population increases by a fixed percentage and because a fixed percentage of a large population is necessarily larger than a small population, the larger the population size, the faster it grows, a population typically grows exponentially when it has ideal conditions with no restrictions on its growth
What do density-dependent factors do? What are some examples of a density-dependent factor?
density-dependent factors are environmental factors whose effects on a population change as population density changes; they tend to retard population growth as population density increases and enhance population growth as population density decreases; so they increase their affect on a population as population density increases; this is a type of negative feedback; resource limitation in crowded populations can stop population growth by reducing reproduction or increasing mortality; some of these factors include: predation, disease, and competition (including interspecific and intraspecific)
Density independent factors: what are they? Examples?
density independent factors are environmental factors that affect the size of a population but is not influenced by changes in the population density; so, they limit population growth but are not influenced by changes in population density; examples include: climate (temperature, humidity), weather, and regular catastrophic events such as fires, hurricanes, and floods
interspecific competition
the interaction between members of different species that vie for the same resource in an ecosystem (ex: food or living space); DIFFERENT SPECIES
intraspecific competition
the interaction between members of the same species that vie for the same resource within an ecosystem (ex: food or living space), SAME SPECIES
semelparous reproduction
creatures who do this expend their energy in a single, immense reproductive effort
iteroparous reproduction
creatures who do this exhibit repeated reproductive cycles throughout their lifetimes
K strategy (aka K selection)
a reproductive strategy in which a species typically has a large body size, slow development, and long lifespan and does not devote a large proportion of its metabolic energy to the production of offspring; so, it maintains a population near the carrying capacity of the environment, and these species often have a large body size, low reproductive rates, long life spans, and they inhabit stable environments
R strategy (aka R selection)
a reproductive strategy in which a species typically has a small body size, rapid development, and short lifespan and devotes a large proportion of its metabolic energy to the production of offspring; so, it emphasizes a high growth rate, and these organisms typically have a small body size, high reproductive rates, short life spans, and they inhabit variable environments
Type 1 survivorship curve
mortality is greatest in old age; the probability of survivorship decreases with age; K-strategists
Type 2 survivorship curve
mortality is spread evenly across all ages
Type 3 survivorship curve
mortality is greatest among the young; the probability of survivorship increases with age; r-strategists
metapopulation
a population that is divided into several local populations among which individuals occasionally disperse (immigrate and emigrate); metapopulations are becoming more common as humans alter the landscape by fragmenting existing habitats to accommodate homes and factories, agricultural fields, and logging, as a result, the concept of metapopulations, particularly as it relates to endangered and threatened species, has become an important area of study in conservation biology
source habitat
a good habitat in which local reproductive success is greater than local mortality, surplus individuals in a source habitat may disperse to other habitats; these are the preferred habitats, they increase the likelihood of survival and reproductive success for the individuals living there, local individuals disperse from source habitats
source population
populations that live in source habitats, they 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
a lower quality habitat in which local reproductive success is less than local mortality; lower quality habitats, the individuals living there may suffer death, or, if they survive they will have poor reproductive success
sink population
the population living in sink habitats, 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
what was the world’s population in 2003?
6.3 billion
How has the per capita growth rate declined from its peak in 1965?
Per capita growth rate has declined from its peak in 1965 of about 2% per year to 1.3%
What do scientists predict about population growth by the end of the 21st century?
Scientists predict zero population growth by the end of the 21st century
population characteristics in highly developed countries
low birth rate, low infant mortality, low fertility rate, long life expectancies, and high average income
population characteristics of developing countries
high birth rate, high infant mortality, high fertility rate, short life expectancies, and low average income
people overpopulation
a situation in which there are too many people in a given geographic area; results in pollution, environmental degradation, and resource depletion
consumption overpopulation
a situation in which each individual in a human population consumes too large a share of resources; results in pollution, environmental degradation, and resource depletion
Is it possible for a country to have replacement-level fertility (the number of children a couple must produce to ‘replace’ themselves) and still experience population growth?
Yes
What does young age structure cause?
young age structure causes a positive population growth momentum as large pre-reproductive age group matures
