Ngoc- Chapter 10 Population Dynamics

Populations are dynamic entities that vary in …………….

size over time

What can lead to exponential growth?

Dispersal

Logistic growth

increase rapidly at first, then stabilize as the population reaches carrying capacity.

Carrying capacity

Maximum population size that can be supported indefinitely by the environment.

eutrophication

the process of a water body becoming overly enriched with nutrients

Carrying capacity

the maximum population size that can be supported indefinitely by the environment

Population Fluctuation

numbers rise and fall over time.

A rapid increase in a population can cause a population………

OUTBREAK!!!

What is important in disease outbreak?

POPULATION FLUCTUATION

Population cycles

Alternating periods of high and low abundance occur at regular intervals.

What can cause populations to cycle?

Delayed density dependence

For example: Number of individuals born in one time period can be influenced by population densities or other conditions that were present several time periods ago.

Who reproduce quicker? a predator or a prey?

A prey

If predator population is small/big, prey population may increase, then the predators will increase, but with a time lag

small

The risk of extinction increases in populations that fluctuate in size are…….

small

A population that fluctuates in size has a slower/faster growth rate than one that does not vary.

slower

What does σ represent?

degree of fluctuations in population growth rate

What does λ represent?

population growth rate

What do large fluctuations lead to?

high risk of extinction

What is a effective population size?

Number of individuals that can contribute offspring to the next generation.

Risk factors for extinction

1. Genetic (genetic drift, interbreeding)

2. Demographic (Stochasticity, Allee effect)

1. Environmental (Natural disasters, Stochasticity)

Chance events influence which alleles are passed on to the next generation. Alleles can be lost or become fixed (frequency of 100%).

Genetic drift

(mating between related individuals) can increase the frequency of homozygotes, including those that have two copies of a harmful allele.

Interbreeding

Chance events (“bad luck”) affect survival and reproduction of individuals.

Example: In a population of ten individuals, a storm wipes out six.

Demographic stochasticity

Population growth rate decreases as population density decreases. At high/low densities, individuals may have difficulty finding mates

Allee effects…………….low

erratic or unpredictable changes in the environment (Think: wet vs. dry years)

For ex: Yellowstone grizzly bear population growth rate varies from year to year.

Environmental stochasticity

(floods, fires, etc.) can eliminate or greatly reduce even large populations and play a role in extinctions

natural catastrophes

What extinction risk factors given that the avg. population growth rate is constant, but the fate of individuals is affected?

In demographic stochasticity

What extinction risk factors given that there is a change in the overall population growth rate (good years and bad years for that species)

In environmental stochasticity

What has existed in some form or another since the dawn of civilization?

Whaling

Mechanized Whaling in the 1800’s

•Dramatically improved the ability of Whalers to bring down animals

•Whale stocks dramatically declined during this time

classic technique used by wildlife managers to asses the health of a specific population. It Has been used to assess specific management actions and their potential impacts

PVA (Population Viability Analysis)

What is special about K value?

It was arbitrarily set and was found to not significantly effect the difference between harvest and non-harvest models

What model do PVA use?

model that incorporates harvest and demographic stochasticity

Populations exhibit………(4 factors)

exhibit exponential, logistic, population fluctuations (random), and population cycles

What factors can lead to fluctuations? (3 factors)

changes in food supply, environmental conditions, and predator abundance

Large/Small populations are at greater risk of extinction by genetic, demographic, or environmental factors

Small