BIOL 230 - MT 2 Flashcards
Communitites
Groups of interacting species in the same place at the same time.
Taxonomic affinity (being of the same taxa), guild (Species that use the same resource), functional group (Similarly functioning, e.g, nitrogen fixing plants).
Key elements of community structure:
Species composition
Species’ ecological inter-relationships
Species diversity
Community structure
Set of characteristics that shape communitites.
Descriptive in nature, but provides the basis for hypotheses and experiments to understand how communities work.
Species richness
The number of species in a community
Species evenness
Relative abundances compared wth one another.
What two aspects does species diversity combine?
Species richness and evenness
Biodiversity examples
Genetic diversity within a population
Diversity of communities at larger scales
Species evenness visualized with rank abundance curves
The steeper the slope the less even the community.
Species accumulation curves
Species richness plotted as a function of total number of individuals counted.
When most or all species in the community are accounted for the graph levels out.
Species-area relationship
Species richness increases with area sampled
In the theory of island biogeography which islands have the steepest curve on a species richness to area graph?
Islands far away had the steepest line and near islands had the flattest.
What did the island biogeography theory state
There appeared to be an equilibrium number of species on the islands which was dependent on their size and distance from the mainland.
Change in species richness is equal to what?
Speciation - extinction + immigration
Describe the equilibrium model of biogeography
There is a point where the immigration and extinction rates are equal.
If S drops below the equilibrium value, there are more resources and space for the entry of new species.
If S increases above the equilibrium the likelihood of species going extinct increases.
The effect of S on extinction rates (equilibrium model).
When S is small, life is easy, low competition and high population sizes means the extinction rate is low.
As S gets larger the more resources will be used up. Species will experience a reduction in density, increasing extinction probability.
When S is very high any disturbance or random fluctuations in population size is increasingly likely to wipe out the small populations. High extinction rate.
What is the main thing that affects extinction rate?
Area.
Rates are expected to shift higher on smaller islands but remain lower on large islands.
Effect of S on immigration rates
When S is small, most newly arriving individuals will represent a new species; immigration rate of new species is high.
As S increases, the species immigration rate decreases because the odds of a newly arrived individual representing a new species is lower.
At high S values there are fewer potential new species left at the source so “new” species run out. Immigration rate approaches zero.
What is the immigration rate mainly influenced by? (Islands)
Isolation distance.
The immigration rates on further islands are lower as the island is harder to reach. Islands closer to the source have higher immigration rates.
Biogeography
Patterns of species composition and diversity across geographic locations.
In general what is the correlation between latitude and species richness?
Lower latitudes have many more and different species than higher latitudes.
Can also vary by region of the world even at similar latitudes.
Species diversification equals:
Speciation rate - extinction rate
What are the three main hypotheses on why the tropics have the highest species richness?
Diversification rate hypothesis
Diversification time hypothesis.
Carrying capacity hypothesis
Diversification rate hypotheses
The tropics have the most land area on Earth with stable temperatures.
Cradle hypothesis: Higher speciation rate in tropics
Museum hypothesis: Lower extinction rate in the tropics
Carrying capacity hypothesis
Due to higher productivity in the tropics, the tropics have a higher carrying capacity than temperate areas.
Could also explain the reverse latitudinal pattern seen in sea birds; coastal oceans are most productive at higher latitudes.
Diversification time hypothesis
The tropics have been more climatically stable over time, allowing species to have had more time to evolve.
Temperate and polar regions have undergone severe climatic changes.
Gamma diversity
Regional patterns of species diversity
Driven by dispersal across the landscape
Alpha diversity
Local patterns of species diversity and composition
Driven by physical conditions and species interactions.
Beta diversity
Local and regional scales are connected by turnover; the difference in species diversity and composition from one community type to another across the landscape.
Asymmetric interspecific competition
Often the effects of competition is unequal, or asymmetrical and one species is harmed more than the other.
Can lead to one species driving another to extinction when they share the same limited resource.
Competition definition
A non-trophic interaction in which individuals of the same species or different species are harmed by their shared use of a resource that limits their ability to grow,reproduce or survive.
Intra vs interspecific competition
Intraspecific competition is competition between individuals of the same species. Leads to density dependent population growth and sets K.
Interspecific competition is between individuals of different species. (General focus when considering community structure and species richness).
Exploitation competition
Reducing access to a recourse by reduction of the availability of that resource.
Indirect effect
Interference competition
Reducing access to a resource by directly interfering with a competitor.
Direct effect.
Competition exclusion principle
Two species that use a limiting resource in the same way cannot coexist indefinitely.
Predicted outcome of two species using the same limiting resource in the same way.
