ch 11 ecology

demographic transition

The shift from high birth and death rates to low birth and death rates as a population develops.

demographic stochasticity

Random changes in births and deaths that cause population size to fluctuate (especially in small populations)

delayed density dependence

population growth is affected by population density from an earlier time, causing population size to fluctuate around carrying capacity (K)

source population

population in good habitat where the population can grow and individuals can disperse to other populations.

sink population

population in poorer habitat that cannot sustain itself and depends on individuals immigrating from a source population to survive.

rescue effect

Immigration from other populations increases population size and reduces the likelihood of extinction.

• High immigration increases population size, making extinction less likely

what types of population growth do invasive species often show?

exponential growth, especially when they first enter a new environment.

why might we expect populations to fluctuate around their carrying capacities? Explain the math.

because resources, birth and death rates, and predation risk change over time

• N < K: population can increase.

• N > K: population tends to decrease

three factors that may increase extinction risk for small populations.

• Genetic drift and inbreeding: (less genetic variation).

• Allee effects (difficulty finding mates).

• Environmental stochasticity (random events like disease or harsh weather)

Why is habitat fragmentation bad for populations?

isolates populations, reduces migration and colonization, and increases extinction risk.

an example that could cause a time lag, and how it would affect population growth.

A population grows rapidly, but food becomes limited only after a time lag. The population keeps growing before resources run out, then crashes, causing population size to fluctuate around carrying capacity

How does the ratio of extinction/colonization affect metapopulations?

A lower ratio favors metapopulation persistence; a higher ratio increases extinction risk.

extinction rate and colonization rate inequalities

• e < c: Colonization exceeds extinction, so the metapopulation increases.

• e > c: Extinction exceeds colonization, so the metapopulation declines and may disappear.