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Definition
All populations of a give type of organism.
the set of all populations whose individuals could interbreed if given the opportunity (biological def) OR all the individuals whose measured traits have defined limits (morphological def). |
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| How do species, populations, and individuals fit together? |
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| Populations that are structured into local groups (ie. flock), sometimes family, sometimes not. |
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| A patchy set of scattered demes with little interaction |
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Easy for animals: physically separate animals
Plants and other modular org: genetic individuals may be composed of one component or many. |
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| The number of different species or organisms found in an area |
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| What is the overall pattern for species richness globally? |
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Definition
| Highest in the Tropics, lowest near the Poles, and intermediate/variable in between. |
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| What is the pattern of species diversity in the temperate zones? |
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Definition
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| Questions that are still unknown about species richness |
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Definition
Is one value of species diversity what it should be and the rest need to be explained?
Should we have on line for the species richness pattern throughout the world and is that line biologically meaningful? |
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| What is the number one contributor of species richness? |
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Definition
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| What are aspects of species richness that define it? |
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Definition
Species added (speciation) and species removed (extinction)
[image] |
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| What are some issues/assumptions with the graphical model of species richness? |
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Definition
1. all taxa in the region react similarly
2. the shapes are all similar in all the different[image] latitudes
3. the curves retain their shapes over time |
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| What are some hypothesizes (theoretical argument) for the species richness pattern? |
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Definition
1. Area hypothesis
2. Productivity hypothesis
3. The Museum Hypothesis |
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| What is the area hypothesis |
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Definition
Physical Mechanism
Through study of plate tectonics, over the last 100 million years ish there have been large continental landmasses across the Tropics, which allow for more species as more land = more species
Argues that more area means more room for species - implying with more area, populations are able to exist at high abundance and those features will make them less likely to go extinct as a result of stochastic events (random)
[image] |
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| Some issues that are wrong with the area hypothesis |
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Definition
| Cons: only works well for the recent past and when most land is tropical (circumstantial cause) |
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| The Productivity Hypothesis |
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Definition
Ecological mechanism
good growth conditions and survival year round in the tropics - plants more productive which means everyone more productive - predators become numerous so prey held down to low densities so less likely to be driven to extinction by competition. - predators can persist and specialize because food supply is abundant, therefore also won't be driven out by competition -result is high species richness
Greater carrying capacity of tropical habitats: more productive large populations or lots of low abundance populations existing long term because the habitat is seldom disturbed.
[image] |
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Definition
| The density of individuals within a given population (not necessarily community or larger scale cases) |
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Evolutionary mechanism:
Disturbances like fires and floods have occurred more severely and more often at higher latitudes, therefore resulting more extinctions per unit time. Tropical zones have some large scale disturbances, but have maintained tropical conditions (so less extinctions). Doesn't mean the rates of extinction and speciation are different, just that the tropics have a more available accumulation time.
[image] |
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| Seeing the museum hypothesis as having low extinction rates |
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Definition
| High tropical richness is suspected to arise due to evolutionary rate differences and the museum hypothesis could insinuate low extinction rate but speciation is similar everywhere |
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Definition
| The tropics exhibit high speciation rates but extinction is similar everywhere |
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| Out of The Tropic hypothesis |
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Definition
| Using the fossil record of bivalve molluscs, Jablonski and co-workers found that speciation, extinction, and movement of taxa all operated differentially at each timepoint so the tropics are a museum, cradle, and exporter of taxa all at the same time |
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| Temperate deserts have very few species per unit area (fewer than the number observed in most temperate habitats). This pattern is most consistent with: |
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Definition
| The productivity hypothesis |
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Term
| What are some ways that can add to species richness? |
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Definition
In the long term, speciation is the only way to add species
In the short term, species are more likely to be added through dispersal movements from other regions (through colonization or immigration |
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Term
| What are the two factors that determine species richness in the short term ecologically? |
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Definition
| immigration and extinction (speciation is possible but unlikely in the period of weeks to centuries so is neglected) |
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Term
| The Area Hypothesis says that area determines species richness, but by what mechanism? What does area influence, ecologically? |
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Definition
- Area controls resources (ex territoriality is a determinant of bird density)
- Area influences mainly extinction rate |
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| How do org reach new sites/islands? |
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| passive through transport with other animals |
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| Equilibrium Biogeography model |
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Definition
| Supply and cost curve - and shifts up and down by isolation distance and size of island |
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