Population Ecology

the study of interactions between organisms & their environment

- includes biotic & abiotic factors

the study of populations in relation to the environment, including environmental influences on density and distribution, age structure, and population size

the presence or absence of species from an area and why

• the pattern of spacing among individuals within the boundaries of the population
• clumped, uniform, random

the area is inaccessible or there was insufficient time for the species to move to that area

habitat selection

• predation
• parasitism
• competition
• disease

• chemical: water, oxygen, salinity, pH, soil nutrients
• physical: temperature, light, soil structure, fire, moisture

• a group of individuals of a single species that are close enough together to interbreed
• key features: size, range, density

• population's size divided by its range (how widely a population is spread)
• individuals/unit area

(In aquatic biomes, density is measured in volume.)

If resources are clustered or spatial proximity to other individuals enhances fitness, populations may be grouped together.

- most common among organisms ex. flocks and herds

The distribution of individual trees or other organisms can appear to be random, with no clear pattern to where they occur.

- common among areas with water and wind current

When resources are limited or predators target a single species, an individual might be better off if it is as far from others as possible, producing a uniform pattern of distribution.

mark-recapture

- Biologists capture individuals, mark them in a way that doesn't affect their function or behavior, release them back into the wild, and then capture a 2nd set of individuals, some of which were previously marked.

• birth and immigration: contribute to population increase
• death and emigration: contribute to population decrease

• age-specifc summary of the survival pattern of a population
• best made by following the fate of a cohort, a group of individuals of the same age
• graphed using a survivorship curve

• type I: low death rates during early and middle life, then an increase among older age groups (humans)
• type II: constant death rate over the organism's life span (small mammals)
• type III: high death rates for the young, then a slower death rate for survivors (clams, butterflies)

• describes population growth in an idealized, unlimited environment
• This is because individuals will continually reproduce, so through time more and more individuals contribute to the growing population.
• intrinsic growth rate (r) is constant through time
• j shaped curve

- intrinsic growth rate: maximum rate of growth when no environmental factors limit population increase

• describes how a population grows more slowly as it nears its carrying capacity
• more realistic population model, since exponential growth cannot be sustained for long in any population
• s shaped curve

- carrying capacity (K): maximum population size the environment can support

At high population density, individuals may be more vulnerable to resource availability, predation, and infection

• factors that influence population size without regard for the population's density
• include events like severe drought or a prolonged cold period

competition between individuals of a single species

competition that occurs between individuals of different species