Unit 3 Ecosystems Topic 6: Population ecology

Populations All of the individuals of a species in a given area at the same time Characteristics of populations – Size (N) – Density – Distribution – Sex ratio – Age structure Clumped Uniform Random

Population Size is affected by: Additions: – Birth – Immigration Subtractions – Death – Emigration Change in population size: N=(birth+immigration)-(death+emigration)

Population growth Growth occurs if inputs are greater than outputs. Change in population size: N=(birth+immigration)-(death+emigration) Under ideal conditions, the intrinsic growth rate is observed. This is the maximum potential for growth of a population. It is essentially the maximum amount of offspring that a population could have, if all females of reproductive age give birth to the maximum number of offspring they are capable of.

Population growth: Exponential Exponential growth is defined as a rate greater than 1. Occurs in populations… – That are introduced to a new area – That are rebounding from a catastrophe Cannot be sustained indefinitely. Why?

K = carrying capacity Max. size that environment can support with no degradation of habitat. Varies with changes in resources. K = carrying capacity Max. size that environment can support with no degradation of habitat. Varies with changes in resources. Logistic rate of growth So, can populations continue to grow exponentially?

Exceeding Carrying Capacity Members of populations which exceed their resources will die or move to an area with more resources. Figure 8-6

Population growth general patterns

Predator/prey population cycles

What do you think the primary producer graph looks like?

Predator/prey population cycles

Population regulation Limiting factors control population growth Regardless of pop. density, these factors are the same for all individuals. The effects of these factors are influenced by population density. Organisms that are more crowded: Compete more for resources Are found easily by predators Spread disease and parasites more readily Density independent – Abiotic (precipitation, temperature, acidity, salinity, etc.) – Catastrophic abiotic (flood, fire, volcanic eruption, tsunami, earthquake) Density dependent – Biotic (food supply, disease, parasites, competition, predation)

What determines reproductive capacity of a population? – sex ratio (how many females vs. males?) – generation time (at what age do females reproduce?) – age structure (how many generations reproduce?)

Reproductive strategies K-selected – late reproduction – few offspring – invest a lot in raising offspring primates coconut r-selected – early reproduction – many offspring – little parental care Invertebrates many plants K-selected r-selected

More generalized characteristics of r and K selected species

Survivorship curves (Generalized strategies) What do these graphs tell about survival & strategy of a species? Human (type I) Hydra (type II) Oyster (type III) Percent of maximum life span Survival per thousand I.High death rate in post-reproductive years II.Constant mortality rate throughout life span III.Very high early mortality but the few survivors then live long (stay reproductive)

Populations of r and K strategists Populations of k strategists tend to grow exponentially when initially established and then become stable around a carrying capacity. Populations of r strategists tend to have periods of rapid growth (births) followed by sharp declines (most young do not survive). Which is which? Pop. size

Populations over time Evolution occurs at the level of the population. What is survival of the fittest? How can community dynamics create biological diversity? How can climatic changes create biological diversity?