Chapter 14

Interactions in Ecosystems

Habitat and niche

Habitat-all biotic and abiotic factors in the environment where the organism lives

Niche-physical, chemical, and biological factors a species needs to survive

Habitat = where; niche = how

Competitive exclusion

The principle of two species competing for the same resources and resulting in one species gaining the advantage– The other species can be pushed

into another niche or possibly become extinct

– Could also result in Niche partitioning (different parts being

used) Evolutionary response (divergent

evolution)

Ecological equivalents

Species that occupy similar niches but in different geographical regions

Different regions means they DON’T compete for the same resources

Symbiosis

Close and permanent relationship between different species

3 types–Commensalism–Mutualism–parasitism

Commensalism

One species benefits but the other is neither helped nor harmed

Ex: peregrine falcon and red-breasted goose

Mutualism

Both species benefit Ex: lichen (green alga and a

fungus)

Parasitism

One species benefits and the other is harmed

Harmed species does not die Benefiting species lives off

tissues of the host

Population density

Population density-measurement of the number of individuals in a defined space or area

Can be used to determine the health of the population and ecosystem

Population dispersion indicates how species interact within the ecosystem

Survivorship curve

Generalized diagram showing surviving members of a species over time from a measured set of births

Survivorship curve

Survivorship types

Population growth

Change in size of a population over time

Studied by bacterial growth No linear growth Have “J” curve growth cycles

– Exponential growth– Population explosion– Reaches carrying capacity; “S” curve

Exponential growth

Occurs when individuals in a population reproduce at a constant rate

Population becomes larger over time

Logistic growth

Slowing or stopping of population growth after a period of exponential growth

Due to reduction in resources

Growth curves

Limiting factors

Density-dependent– Increased effect as population

increases– Include disease, competition,

parasites Density-independent

– Affect all populations regardless of size

– Abiotic factors like temperature, drought, flood, habitat disruption

Mobility

Immigration-movement of individuals into a population

Emigration-movement out of a population

Succession

Natural changes that take place in the communities of an ecosystem

3 types– Primary– Secondary– climax

Primary succession

Colonization of new sites by organisms

First organisms are pioneer species

Example:– Forming new plant and animals

colonies on volcanic rock

Secondary succession

Changes in a community that occur after disruption by a natural disaster or human interference

Takes less time than primary succession to reach climax

Climax succession

A mature community that undergoes little or no succession

All species in the community have reached their peak