Lecture 18. Introduction to Ecology & Populations

Ecology

The study of how organisms interact with their biotic & abiotic environments

Biotic factors in environment

Living thing or something that derives from a living thing

Abiotic factors in environment

Things that are physical rather than biological; not living or derived from a living organism

Ecological systems exist in a…

Hierarchy or organization

Ecological system

System formed by interactions between organisms & their environment

Hierarchy of organization in living systems

Individuals → population → community → ecosystem → biome → biosphere

Individual

Individual organism

Population

Individuals of same species that occupy the same area & have potential to interbreed

Community

Populations of different species living together in a particular area, have the potential to interact

Ecosystem

One or more communities or organisms & the physical (abiotic) environment around them

Biome

Any of Earth’s major ecosystem types, contains communities of organisms with similar adaptations

Biosphere

All ecosystems on Earth

Species (not levels in hierarchy)

Group of organisms that naturally interbreed with each other & produce fertile offspring

Adaptation (not levels in hierarchy)

Heritable characteristic of an organism that improves its ability to survive & reproduce in a particular environment

Population ecology

Study of how individuals in a population of a single species interact with their environment, focuses on factors that influence population density & population growth

Community ecology

Study of how interactions between multiple species affect community structure & organization

Population experience the same…

Environmental factors, resources, & can interact & breed together

Population distribution

Geographical area occupied by a population & are determined by population density

Geographical range

The distribution of a species

Geographic ranges are affected by 3 types of factors…

Abiotic factors, biotic interactions, & anthropogenic effects

Abiotic factors that determine range limits are…

Physical barriers & spatial climate gradients

At range margins

Conditions suboptimal, but not lethal

Beyond range margins

>=1 environmental variables beyond species’ physiological tolerance

Climate & habitat help create…

Range limits

Biotic interactions that determine range limits

Habitat quality & availability & competition

Anthropogenic effects on range limits

Rock pigeons, natural range expansions (cattle egret)

Life history

The schedule of organism’s growth, development, reproduction, & survival

Life history traits

Traits related to number of offspring an organism produces (evolve through selection)

Effects on life history traits set range limits

Reduced capacity to mature, breed, care for offspring, disperse, etc.

Negative effect on life history characteristics can lead to…

Source-sink dynamic at range margins

Population sink

A population that cannot sustain without migrants from healthy source population

Populations are characterized by…

Number & distribution of individuals

Population density

No. of individuals of species per unit area or per unit volume

Mark-recapture method

(Marked animals in 2nd sample)/(Total no. caught in 2nd sample) = (Marked animals in 1st sample)/(Total population size)

Population dispersion pattern

Pattern in which individuals are spaced within their geographic distribution

Clumped dispersion (most common, ex. schools of fish)

Individuals grouped in patches - results from unequal distribution of resources in environment

Uniform dispersion (ex. seabirds)

Individuals distributed evenly - results from interactions between individuals of population

Random dispersion (ex. dandelions)

Individuals distributed randomly or unpredictably - rare given distribution of resources & interactions with other individuals