Ecology 

Study of the interactions of organisms with other organisms and with the physical environment

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Ecological interactions are selection pressures that result in evolutionary change, which in turn affects ecological interactions 

Ecology is wide-ranging 

Habitat – the place where the organism lives

§ Population – all the organisms within an area belonging to the same species

§ Community – all populations interacting at a locale § Ecosystem – encompasses a community of

populations as well as abiotic environment

§ Biosphere – encompasses the zones of the Earth’s land, water, and air where living organisms are found 

Density

population density

§ Number of individuals per unit area 

Distribution 

Population distribution – the pattern of dispersal of individuals across an area (is dependent on availability of resources)

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Resources are nonliving (abiotic) and living (biotic) components of an environment that support living organisms 

Limiting Factors are those environmental aspects that particularly determine where an organism lives 

§ Patterns of distribution: 

Clumped
 Random
 Uniform 

Range 

portion of the globe where the species can be found 

A population’s annual growth rate depends on? 

Number of individuals born each year
§ Number of individuals that die each year
§ Annual immigration and emigration 

Biotic potential 

of a population is the highest possible growth rate

§ Achieved when resources are unlimited

§ Depends primarily on:
§ Usual number of offspring per reproduction § Chances of survival until age of reproduction § How often each individual reproduces
§ Age at which reproduction begins 

Cohort  

term used to describe population members that are same age and have same chances of surviving 

probability of cohort members surviving to particular ages

§ If we plot the number surviving at each age, a survivorship curve is produced 

 § Type I Survivorship: Mammals

§ They survive well past the midpoint of the life span, and death does not come until near the end of the life span

§ Type II Survivorship: Hydras, songbirds, and small mammals

§ Survivorship decreases at a constant rate throughout the life span

§ Type III Survivorship: Many invertebrates and fishes § Most individuals will probably die very young 

Age structure diagrams

§ From the perspective of population growth, a population contains three age groups

§ Prereproductive (Pyramid shaped diagram) § Reproductive (Bell shaped diagram)
§ Postreproductive (Urn shaped diagram)

§ Populations differ according to what proportion of the population falls in each age group 

1. Biotic potential of population along with other factors, such as age structure

2. Availability of resources as well as other environmental factors 

Logistic Growth – as resources decrease, population growth levels off

§ S-shaped curve with 4 phases
Lag phase – Growth is slow because the number of

individuals in the population is small

Exponential growth phase – Growth is accelerating due to biotic potential

Deceleration phase – The rate of population growth slows because of increased competition among individuals for available resources

Stable equilibrium phase – Although fluctuations can occur, little, if any, growth takes place because births and deaths are about equal 

 – total number of individuals the resources of the environment can support for an extended period of time

§ Stable equilibrium phase of logistic growth is at carrying capacity

§ Number is not a constant and varies with the circumstances and the environment