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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
Distribution deals with
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
If dispersal limits a species' distribution, that means __
the area is inaccessible or there was insufficient time for the species to move to that area
If behavior limits a species' distribution, this can be due to __
Biotic factors that can limit a species' distribution may include __
Abiotic factors that can limit a species' distribution may include __
- 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.)
clumped (clustered) distribution pattern
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
random distribution pattern
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
uniform (regular) distribution pattern
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.
In cases in which it is hard to count the individuals in a population, the __ method is used.
- 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.
factors affecting the size of a population
- 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
3 general types of survivorship curves
- 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
density dependent factors (K-selection)
At high population density, individuals may be more vulnerable to resource availability, predation, and infection
density-independent factors (r-selection)
- 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