BIOLOGY 1500 OUTLINE FOR CHAPTER
Community and Population Ecology
Definitions:
A community: populations of different species living in a particular place and potentially
interacting with each other
A population: a group of individuals of the same species living in a particular place
Classification of Communities, according to:
1. Physical appearance. Such as forests, grasslands, deserts, scrublands…each has a
dominant plant species
2. Species diversity:
a. High diversity: such as in tropical rain forest or coral reef.
b. Low diversity: such as in tundra or boreal coniferous forest
3. Niche structure: how many organisms are in each trophic level, and if they were
specialists versus generalists.
Physical appearance and Terrestrial Biomes
- Tundra: very cold, low biodiversity
- Boreal forest: dominance of coniferous forests
- Temperate deciduous forest: dominated by trees that lose their leaves every year.
Warm, most summers and mild winters. More diversity than tundra but less than
the tropical forests
- Grasslands: dominated by grasses
- Hot deserts: dominated by cacti plants, low biodiversity.
- Savanna: dominated by grasses with scattered trees. Usually in transitional zones
between forests and deserts or grasslands. Known for having wildlife as in Africa.
- Tropical forests: could be evergreen or deciduous. Dominated by tall trees. High
biodiversity
Community structure and biodiversity
Varies depending on biome. Tundra biome has fewer trophic levels in the food web
and fewer species at each trophic level (low biodiversity). Temperate rain forest has
more trophic levels, and more species at each level (high biodiversity).
Species present in a community
- native species: species present since recorded history began.
- Invasive species: organisms introduced accidentally or intentionally by people
o European starling, zebra mussel, purple loosestrife, giant hogweed
- Indicator species: organisms that responds quickly to environmental stress
o Tadpole snails, tubifex are examples of indicators of polluted water
o Green caddis, trout are examples of indicators of clean water
- Keystone species: species that maintains the structure of a community
o Sea otters prevent sea urchins from destroying kelp populations.
- Foundation species: species that restores a community if the community is removed
o Elephants break trees to allow for understory plants to survive
Species interactions
- Competition: two or more individuals scrambling or fighting for the same resource.
Can be within the same species or between species
- Mutualism: both species benefitting
- Commensalism: only one species is benefitting, the other is indifferent.
- Parasitism: a species living in or on another organism and feeding on it until the
host is killed.
Succession in species
- is a generally predictable change in community composition over time
o primary succession: the progression of species from bare ground to a climax
community (slow, and soil did not exist initially)
o secondary succession: the restoration of a previously existing community
from a disturbance (rapid, soil was already present), also stabilizing of sand
dunes.
Populations (Terminology)
- population size = (births+immigration)-(deaths+emigration)
- intrinsic rate of increase (r)
o the rate at which a population increases in size
- carrying capacity of the environment (K): number of individuals the environment
can support.
o K also an important part of biological resistance. It factors all the factors that
restrict population growth (such as limited space, food shortage)
- Age structure: many young individuals usually means rapid growth in the future.
Many older individuals usually means slower growth in the future.
Exponential versus Logistic population growth.
- exponential growth involves ever-increasing rates of growth; produces J-curve.
- Logistic growth starts out like exponential growth, but slows down as it reaches K;
produces S-curve.
r-selected and K-selected species
- r-selected species have r-selected reproductive strategy
o have high reproductive rates
o tend to occur in unpredictable environments
o typically have type III survivorship curves (such as fish)
- K-selected species have K-selected reproductive strategy
o Occur near carrying capacity of their environments
o Experience effects of population density
o Have low reproductive rates, high parental care
o Have type I survivorship curves (such as human)
- Most r-selected organisms are generalists (except parasites)
- Most K-selected organisms are specialists (except humans)