Lecture 16: Biogeography Flashcards
Biogeography
the study of patterns of species composition and diversity across geographic locations.
Lower Latitudes vs higher latitudes
- Lower have many more, and many different species than higher latitudes
Species richness
- The same community type or biome can vary in species richness and composition depending on its location on Earth.
Spatial scales
- are interconnected in a hierarchical way, with the patterns of species diversity and composition at one spatial scale setting the conditions for patterns at smaller spatial scales
Global scale
- entire world
- Species have been isolated from one another, on different continents or in different oceans, by long distances and over long periods
- Rates of speciation, extinction, and dispersal help determine differences in species diversity and composition
Regional scale
- areas with uniform climate; the species are bound by dispersal to that region
Regional species pool
- all the species contained within a region (gamma diversity)
- Provides the raw material for local assemblages and sets the theoretical upper limit on species diversity for communities
- All species available that can live in the habitats
Landscape
- Topographic and environmental features of a region
- Species composition and diversity vary within a region depending on how the landscape shapes rates of migration and extinction.
Local scale
- equivalent to a community
- Species physiology and interactions with other species are important factors in the resulting species diversity (alpha diversity)
Beta diversity
- Change in species number and composition, or turnover of species, from one community type to another
Global Biogeography
Global patterns of species diversity and composition are controlled by geographic area and isolation, evolutionary history, and global climate
- Some species in one part of the world are similar to species in another part
Two global patterns
- There is a gradient of species diversity with latitude (higher latitudes, diversity goes down)
- Earth’s land mass can be divided into six biogeographic regions
Vicariance
evolutionary separation of species by barriers such as those formed by continental drift
ex. The large flightless birds (ratites) had a common ancestor from Gondwana. After isolation on different continents, they evolved unique characteristics, but retained their large size and inability to fly.
Global patterns of species richness should be controlled by which three processes?
- Speciation
- Extinction
- Dispersal (if rates are similar everywhere, then species richness should reflect a balance between extinction and speciation)
Species Diversification rate
- The net increase or decrease of species over time
- Subtracting extinction rate from speciation rate
Species diversification time
- The tropics are thought to have been more climatically stable over time, and species have had more time to evolve.
- Temperate and polar regions have undergone severe climatic changes such as glaciation, disrupting species diversification.
Productivity or carrying capacity
- Higher carrying capacity and productivity in the tropics (terrestrial)
- some very productive habitats, such as estuaries, have low species diversity
Regional Biogeography
Regional differences in species diversity are influenced by area and distance, which determine the balance between immigration and extinction rates
- species richness increases with area sampled
Species–area curves
- plots species richness (S) of a sample against area (A) of the sample.
- The relationship between S and A is estimated by linear regression: S = zA+c
- z=slope, c=y-intercept
- S and A are transformed into logarithmic values to obtain a straight line
Island sizes
- large islands have more species than small islands
- Larger islands closer to mainland, smaller islands further away
- Populations on small islands have higher chances of going extinct, due to small population size and increased effects of competition and predation.
The equilibrium theory of island biogeography
- The number of species on an island depends on a balance between immigration or dispersal rates and extinction rates
- This equilibrium number is the number of species that should theoretically “fit” on the island, irrespective of the turnover, or replacement of one species with another
The Biological Dynamics of Forest Fragments Project
- Explains why more species are found on large islands than on small islands
- Four different sizes of forest plots were set up: 1, 10, 100, or 1,000 hectares.
- Control plots were surrounded by forest. Fragments were surrounded by logged land.
- Study design of conservation reserves and maintenance of species diversity
- project shows that most forest fragments are too small to maintain all their original species. Habitat fragmentation is likely to result in the loss of many species
Habitat fragmentation
- creates large edge effects at the transition between forest and matrix habitat (can contribute to local extinctions)
- ex. trees at the edge are exposed to more light, higher temperatures, wind, fire, and diseases.
Edge effects & forest regenerates
- If forest regenerates, secondary succession takes place and edge effects decrease
- if not, the area subjected to edge effects may increase in size
Burning of forests
- Burning is used regularly and keeps the forest edges in a constant state of disturbance. Fire-tolerant species increase and edge effects extend into the fragment, reducing its effective size
- In order to have forest practices to maintain species richness, need to set aside massive fragments to preserve
