Ecology

110 flashcards by MentisLibrary

How organisms interact with each other and their environment: energy flow and productivity, population growth, species interactions and succession, biomes, nutrient cycles, biodiversity and conservation.

What does ecology study?
The interactions between organisms and their environment, and the distribution and abundance of life that results from them.
List the levels of ecological organization from smallest to largest.
Organism, population, community, ecosystem, landscape, biosphere.
What is the difference between a population and a community?
A population is all the individuals of one species in an area; a community is all the populations of all species living there and interacting.
What does an ecosystem include that a community does not?
The abiotic environment: sunlight, water, temperature, soil and the chemical elements that cycle through the living and non-living parts together.
Habitat or niche: which one is the address and which is the occupation?
Habitat is the address, the physical place a species lives. The niche is the occupation, the full set of resources and conditions it uses and its role in the community.
Fundamental niche versus realized niche
The fundamental niche is the full range of conditions a species could use with no competitors or predators. The realized niche is the smaller part it actually occupies.
What is a trophic level?
A feeding position in a food chain: producers, primary consumers, secondary consumers, tertiary consumers, and decomposers alongside them.
What is gross primary productivity?
The total rate at which producers capture energy and fix it into organic compounds, before any of it is respired away.
How is net primary productivity defined and calculated?
The energy producers fix minus what they burn in their own respiration: $NPP = GPP - R_a$. It is the new plant matter left for consumers and decomposers.
About how much energy passes from one trophic level to the next?
Roughly 10 percent. The rest is lost as heat in respiration, in undigested material, and in tissue that is never eaten.
Why are food chains rarely longer than four or five links?
Because only about a tenth of the energy moves up at each step, there is too little left above four or five levels to support a viable predator population.
What is a food web?
A network of interconnected food chains that shows most consumers feed on several species and are eaten by several others.
What is a detritivore?
An animal that eats dead organic matter and physically fragments it into smaller pieces.
How do decomposers differ from detritivores?
Decomposers, mainly fungi and bacteria, secrete enzymes and absorb the products, releasing inorganic nutrients back to soil and water.
Why is a pyramid of energy always upright while a pyramid of biomass sometimes is not?
Energy is lost at every transfer, so it must shrink upward. Biomass can invert when fast-reproducing producers are eaten as fast as they grow.
What is biomagnification?
The rise in the tissue concentration of a persistent, fat-soluble pollutant at each higher trophic level.
What is a keystone species?
A species whose influence on community structure is far larger than its abundance would suggest.
What is an ecosystem engineer?
A species that creates, changes or destroys physical habitat, altering resource availability for many other species.
What is a trophic cascade?
A chain of indirect effects in which a change at one trophic level alters abundance two or more levels away.
Top-down versus bottom-up control of a community
Top-down control means predators limit the levels below them. Bottom-up control means nutrient supply and producers limit the levels above.
What is population density and how does it differ from population size?
Density is the number of individuals per unit area or volume; size is the total count in the whole area.
Name the three dispersion patterns and what causes each.
Clumped, from patchy resources or social grouping. Uniform, usually from territoriality or chemical inhibition. Random, when individuals neither attract nor repel each other.
Write and explain the exponential growth model.
$\frac{dN}{dt} = rN$, where $N$ is population size and $r$ is the per capita growth rate. Growth accelerates without limit as $N$ rises.
Write and explain the logistic growth model.
$\frac{dN}{dt} = rN\left(\frac{K - N}{K}\right)$. Growth slows as $N$ approaches the carrying capacity $K$ and stops at $N = K$.
What is carrying capacity?
The maximum population size an environment can sustain indefinitely given its food, water, shelter and space.
Density-dependent versus density-independent limiting factors
Density-dependent factors intensify as crowding rises: competition, disease, predation, waste buildup. Density-independent factors hit regardless of density: frost, flood, fire, hurricane.
Contrast r-selected and K-selected life histories.
r-selected species reproduce early and abundantly with little parental care and short lives. K-selected species mature slowly, produce few well-provisioned young, and live longer.
Describe the three survivorship curves.
Type I: high survival through life with mortality late, plotted as a shoulder then a drop. Type II: constant mortality at all ages, a straight line on a log scale. Type III: heavy juvenile mortality then a flat tail.
What does an age structure diagram predict?
Future growth. A broad base of young age classes means growth ahead; a column shape means stability; a narrow base means decline.
What are the stages of the demographic transition?
Stage 1 high birth and death rates. Stage 2 death rates fall and growth is fastest. Stage 3 birth rates fall. Stage 4 both are low and growth approaches zero.