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 redbreasted 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