Unit 8 - Ecology Flashcards
What is the difference between density, population size, and dispersion in relation to a population?
Density = # of individuals per unit area/volume
Population size = # of individuals total
Dispersion = pattern of how those individuals are spread out or distributed
What general mechanisms cause population sizes to increase or decrease?
Birth (reproductive rate) and immigration (influx of individuals from other areas) result in increase
Death (survivorship curve) and emigration (movement out) result in decrease
Describe the three patterns of dispersion.
- Clumped - individuals are grouped into patches
EX: May be associated with greater availability of food, mating behavior, favorable climate, or better defense against predation
- Uniform - individuals are evenly spaced
EX: May be due to territoriality (defense of a bounded physical space against encroachment by other individuals)
- Random - unpredictable spacing and the position of each individual is independent of others
EX: plants established by windblown seeds
Describe the three survivorship curves.
Type I - flat and high at the start (low death rates during early/middle life) and then drops steeply (increasing death rates for older age classes). Applies to animals that produce few offspring but provide them with good parental care (EX: humans and other mammals)
Type III - drops sharply at the start (high death rates for the young) but flattens out eventually (declining death rates for those who survive the early period of die off). Applies to organisms that produce a lot of offspring but provide little to no parental care (EX: fish release millions of eggs)
Type II - intermediate linear graph; constant death rate over the organism’s life span (EX: invertebrates, lizards)
What does a stair step survivorship curve mean?
Younger individuals have a higher survivorship than older individuals
What is carrying capacity (K) and how does a population that reaches it respond?
Carrying capacity is the maximum population size a specific environment can sustain with the abundance of limiting resources it has.
In a population at its K, birth rate = death rate (zero growth)
Exponential population growth model vs logistic population growth model
Exponential - J shaped curve, occurs in populations with abundant resources and lack of competition (ideal conditions)
Logistic - S shaped curve, occurs in populations who are approaching their carrying capacity, and thus zero growth rate, asymptote = K
K selection vs r selection
K selection - density dependent selection; selects for traits that are favorable at high densities (near carrying capacity with lots of competition); exhibited by Type I organisms like humans
r selection - density independent selection; selects for traits that maximize reproductive success in low densities (uncrowded environments with little competition); exhibited by Type III organisms like hares
What are density independent factors? Give one example.
These are factors that limit growth based on chance
EX: environmental disturbances like droughts or floods occur regardless of the size of the population, keeping it in check by wiping out a random portion of individuals
What are density dependent factors? Give three examples.
These are factors that limit growth based on the density of the population. They either reduce birth rates or increase death rates [negative feedback]
EX 1: Limiting resources - increasing population density intensifies competition for nutrients and other resources which reduces reproductive rates
EX 2: Disease - as population density increases, the transmission rate of a disease also increases which increases the death rates
EX 3: Territoriality - available space for territories or nesting may be limited, thus controlling the population
Community
A group of populations of different species living close enough to interact
Name the three main types of interspecific interactions.
- Competition (-/-)
- Exploitation (+/-) – predation, herbivory, parasitism
- Positive interactions or symbiosis (+/+) or (+/0) – mutualism, commensalism
What is competitive exclusion and when does it occur?
Occurs when two species compete for the same resources. One of the species will use the resources more efficiently and have a reproductive advantage compared to the other, which will eventually lead to competitive exclusion.
This is the local elimination of the inferior competitor
Ecological niche
The specific set of biotic/abiotic resources an organism uses in its environment; the role it has in its ecosystem
*two species cannot coexist permanently in a community if their niches are identical
Resource partitioning
Differentiation of niches that enables similar species to coexist in a community (limits competition because they use different available resources)
How might an ecologist test whether a species is occupying its complete fundamental niche or only a portion of it?
Observe whether the niche size changes after the addition of nutritional resources to the habitat
Fundamental niche vs realized niche
Fundamental niche = niche potentially occupied by the species
Realized niche = the portion of the fundamental niche actually occupied by the species
What is parasitism? Give an example.
A parasite derives its nourishment from another organism, its host, which is harmed in the process
EX: Ticks on dogs
What is mutualism? Give an example.
Benefits both species in survival and reproduction
EX: animals that pollinate flowers or disperse seeds (bee-flower interaction)
Species diversity vs species richness
Species diversity = variety of different kinds of organisms that make up the community (based on # of different species and the relative abundance of each one)
Species richness = # of different species
What are invasive species? How do they harm the environment they are introduced to?
They are foreign organisms introduced to native species
They harm the environment by exploiting a new niche through outcompeting other organisms (capture more available resources → leave fewer for the native species → decreases their survival). They often grow rapidly due to a lack of predators or competitors in this new environment
Food chain vs food web
Food chain = the transfer of food energy up one specific sequence of trophic levels (autotrophs/primary producers → herbivores/primary consumers → carnivores/secondary consumers → decomposers)
Food web = the linking of numerous food chains in a community
Keystone species
Has a pivotal ecological role/niche in the ecosystem despite not being very abundant. If it is removed, the entire ecosystem will collapse
What is ecological succession? Name two types of it.
After a severe disturbance (EX: volcanic eruption) that strips away all existing vegetation, the area is colonized by a variety of species. More species come and replace the original ones as the environment gradually recovers
Primary succession and secondary succession
Describe the process of primary succession
Begins in a lifeless area with NO SOIL (EX: new volcanic island with only rock)
- Only life forms initially present are prokaryotes/protists
- Then the first macroscopic photosynthetic lichen + mosses colonize the area
- Soil gradually develops as rocks weather and organic matter accumulate from the decomposed remains of early colonizers
- Once soil is present, lichen + moss are replaced by grasses, shrubs, and trees
- Eventually the area is colonized by plants that become the community’s dominant form of vegetation
How is secondary succession different from primary succession?
Begins in an area with SOIL still intact (EX: forest after a fire)
Ecosystem
The sum of all the organisms living in a given area and the abiotic factors with which they interact
Energy flow vs chemical cycling
Energy flow - energy enters an ecosystem as sunlight and is converted to chemical energy by autotrophs, passed to heterotrophs in the organic compounds of food, and dissipated as heat.
Chemical cycling - chemical elements like carbon and nitrogen are cycled among abiotic/biotic components of the ecosystem
While chemicals are reused, energy enters, flows through, and exits out
What is the role of detritivores/decomposers? Give examples of them.
Definition: They are consumers/heterotrophs that get their energy from detritus, which is nonliving organic material such as remains of dead organisms, feces, fallen leaves, and wood.
Function: They break down this organic matter from all trophic levels into inorganic compounds (chemical elements) usable by autotrophs/primary producers. When they excrete waste products or die, those compounds are returned to the soil for uptake by producers
EX: earthworms, prokaryotes, fungi
What factors control primary production in terrestrial and aquatic (marine + freshwater) ecosystems?
Terrestrial - temperature and moisture (annual precipitation)
Aquatic - light and nutrients (nitrogen + phosphorous)
How much energy is transferred between trophic levels? Where does the rest go? How does this benefit the ecosystem?
10%
the rest is dissipated as body heat
This limits the abundance of top level carnivores that an ecosystem can support
Energy pyramid
Illustrates the net productions of different trophic levels in tiers and the loss of energy with each transfer [Joules]
Water cycle (biological importance, forms available to life, reservoirs, key processes)
Biological importance - water is essential to all organisms and its availability influences the rates of ecosystem processes, especially primary production + decomposition in terrestrial ecosystems
Forms available to life - all organisms are capable of exchanging water directly with their environment
Reservoirs - oceans»_space;> glaciers + polar ice caps > lakes, rivers, groundwater
Key processes - evaporation (transpiration) of liquid water by solar energy → condensation of water vapor into clouds → precipitation → surface/groundwater flow can return water to oceans
Carbon cycle (biological importance, forms available to life, reservoirs, key processes)
Biological importance - carbon forms the framework of the organic molecules essential to all organisms
Forms available to life - autotrophs use CO2 during photosynthesis and convert the carbon to organic forms (C6H12O6) that are used by consumers
Reservoirs - fossil fuels, soils, the sediments of aquatic ecosystems, the oceans, plant/animal biomass, atmosphere
Key processes - photosynthesis by plants remove atmospheric CO2 while cellular respiration of producers/consumers and burning of soil fuels add it back. Consumers eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.
Nitrogen cycle (biological importance, forms available to life, reservoirs, key processes)
Biological importance - nitrogen is part of amino acids, proteins, and nucleic acids and is often a limiting plant nutrient
Forms available to life - plants can use NH4+ and NO3- [inorganic] and amino acids [organic]. Bacteria can use all those and NO2-. Animals can only use organic forms
Reservoirs - atmosphere (N2 gas)»_space;> soils and sediments of lakes, rivers, oceans > surface water/ground water > biomass of living organisms
Key processes - nitrogen enters an ecosystem mainly thru nitrogen fixation (conversion of N2 to forms that can be used by plants to synthesize organic nitrogen compounds). The NH4+ released by consumers into the soil is converted by bacteria to NO3-, which is used by plants to make proteins and nucleic acids.
↓bacteria ↓
NH4+ → NO3- (nitrification)
NO3- → N2 (denitrification)
Phosphorous cycle (biological importance, forms available to life, reservoirs, key processes)
Biological importance - phosphorous is a major constituent of nucleic acids, ATP
Forms available to life - inorganic phosphate (PO4 3-) which plants absorb and use in the synthesis of organic compounds
Reservoirs - sedimentary rocks»_space;> soil > oceans > organisms
Key processes - weathering of rocks adds PO4 3- to soil slowly → spills into ground water/surface water → taken up by producers → incorporated into organic molecules and passed on to consumers → returned to soil/water by decomposition of biomass or excretion by consumers
Describe two different strategies organisms use to
regulate body temperature and metabolism.
- Endotherms use thermal energy generated by metabolism to maintain homeostasis and constant body temperatures.
- Ectotherms lack efficient internal mechanisms for maintaining body temperature, though they may regulate their temperature behaviorally by moving
into the sun or shade or by aggregating with other individuals.
Describe two adaptations against predation
- Cryptic coloration - prey is camouflaged by its coloring, making them hard to spot
- Aposematic coloration - prey warns that it’s poisonous by being brightly colored
What level of disturbance fosters the greatest species diversity and why?
Intermediate
If the level is too high, frequent and intense environmental stresses will wipe out many species that can’t tolerate them or that grow slowly
If the level is too low, competitively dominant species will be able to exclude less competitive ones. The community will rely on interspecific interactions
Primary production
The amount of light energy converted to chemical energy (in the form of organic compounds) by autotrophs
The amount of all photosynthetic production sets the spending limit for the energy budget of the entire ecosystem
Gross primary production (GPP) vs net primary production (NPP)
GPP = total primary production in an ecosystem NPP = amount of energy available to consumers (NPP = GPP - Ra)
Ra = the energy used by primary producers for autotrophic respiration
How does species diversity affect the population’s resistance to change?
Higher genetic diversity = more individuals that can withstand different selective pressures = higher resistance to environmental disturbances = lower survival of invasive species
Why cannot energy be cycled through an ecosystem?
Second law of thermodynamics - in any energy transfer, some of the usable energy is lost as heat, so the entropy of the universe is always increasing
