Presentation on theme: "Patterns in space Log area Log species number productivity # species Habitat variety # species Latitude # species mainland Log area Log species number."— Presentation transcript:
Patterns in space Log area Log species number productivity # species Habitat variety # species Latitude # species mainland Log area Log species number close far islands
Time during succession Species number Disturbance frequency Species number Millions of years Species number Patterns in time Hundreds of Millions of years Species number
Trophic level # species Two more patterns Body size within taxon # species
1) Why do species numbers increase with area? Log area Log species number PATTERNEXPLANATION ECOLOGICAL PRINCIPLES When sampling area is increased, more habitats will be incorporated. More habitats support more habitat specialists More habitats can serve as refuge. Co-evolution of competitors (niche separation). Universality of spatial variability. Metapopulation theory (more demes, more safety).
Sites are spatially heterogeneous at many scales. Texas by Annual Precipitation
2) Diversity generally increases with productivity. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Higher productivity supports more individuals (biomass). Therefore, more species can attain the minimal viable population size. Most productive environments exclude weak competitors?? Makes some PP relationships unstable?? Minimal viable population size (through demographic stochasticity, Allee effects, genetic drift). productivity # species Competitive exclusion principle. Paradox of enrichment.
Climate dominates site productivity, the interplay of precipitation and temperature. However, climate factors alone do not explain all patterns between ecosystem productivity and biodiversity.
3) A more spatially variable habitat has more species per area. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Habitat variety # species More habitats support more habitat specialists. Co-evolution of competitors (niche separation).
4) Biodiversity decreases between the species-rich equatorial tropics and the species-poor polar regions. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Latitude # species Higher productivity supports more individuals (biomass), therefore, more species. Minimal viable population size (through demographic stochasticity, Allee effects, genetic drift).
Mercator projection Equal-area projection John Terborgh recognized (1973) that the tropics are the largest contiguous earth biome.
4) Biodiversity decreases between the species-rich equatorial tropics and the species-poor polar regions. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Latitude # species Higher productivity supports more individuals (biomass), therefore, more species. The tropics are larger than any another biome, therefore species have lower extinction rates and more opportunities for speciation. Larger ranges are bigger targets for geographical barriers (speciation). Minimal viable population size. Metapopulation theory (more demes, more safety).
5) Higher trophic levels have fewer species. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Trophic level # species Lower productivity supports fewer individuals (biomass), therefore, fewer species. Longer food chains are more unstable. Tendency of predator- prey interactions to cycle. Minimal viable population size.
6) Islands have fewer species than mainlands. 7) Farther islands have fewer species than closer islands. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Species numbers on islands are regulated through the rates of immigration (from mainland) and local extinction. Farther islands have reduced immigration rates. Islands do not have sink species. Metapopulation dynamics. Species numbers are at equilibrium (extinction rates = immigration rates). Source-sink populations. mainland Log area Log species number close far islands
Immigration rate Extinction rate Species number S I P E Island Biogeography (Robert MacArthur and Edward Wilson)
Immigration rate Extinction rate Species number S I P E S* S* is a stable species number. However: species on islands constantly turn over. S* is constant through the balance of extinctions and immigrations
Immigration rate Extinction rate Species number S I P E S1*S1* Farther islands have fewer species because immigrations occur less often. S3*S3*S2*S2* Island distance from mainland increases
Immigration rate Extinction rate Species number S I P E S1*S1* Larger islands have lower extinction rates than smaller islands (because population sizes are larger). S3*S3*S2*S2* Island size increases
Immigration rate Extinction rate Species number S I P E Supertramps get there first: species may have different dispersal and colonization abilities. S*
Extinction rate accelerates with species number: some species may begin to compete or some species may eat another to extinction upon arrival. Immigration rate Extinction rate Species number S I P E S*
Mangrove islands, Florida Keys Daniel Simberloff tested MacArthur and Wilson’s hypothesis on mini- islands off the Florida coast: arthopods
Do species turn over? – Yes. In 1970, Simberloff defaunated four small islands. Islands:Years 0-1Years 1- 2Years 2-3 E E E ST Species held in common between the time before defaunation and subsequent censuses (as fractions):
Does island size affect species number? – Yes. Simberloff reduced island size, by cutting down mangrove trees and counted species before and one year after.
8) Diversity increases during succession. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Only a few early successional species (plants) can deal with the harsh conditions. They pave the way for (presumably more) later successional species. Facilitation model of succession: early successional species pave the way (i.e. create niches) for late successional species. Time during succession Species number
9) Diversity is maximal with intermediate disturbance. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Local, mild disturbance creates a patchwork of sites in various stages of succession. Intermediate disturbance generates maximal habitat diversity for a maximum number of species. Gap model of succession. Competition theory (more niches more species) Disturbance frequency Species number
10) Over millions of years, diversity stays constant. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Mainland diversity may (like island diversity) track a stable equilibrium where extinction rates balance speciation rates. Metapopulation theory (for the extinction part) Co-evolution of competitors: empty niches tend to fill. Millions of years Species number within taxon
Speciation rate Extinction rate Species number S The more species, the more speciation events. Speciation is accelerated at low species densities, because there are more ecological opportunities. The extinction rate increases, because, as the number of species in the province increases, more populations will become small and have an increased risk of extinction. S*
Speciation rate Extinction rate Species number S Smaller provinces Smaller continents have fewer species, because extinction rates are higher speciation rates lower.
Larger continents have more species
10) Over hundreds of millions of years, diversity increases. PATTERNEXPLANATION ECOLOGICAL PRINCIPLES Geologic and climate change opens new habitable spaces. Evolutionary key innovations spark evolutionary radiations of new families. New niches come into existence with the arrival of key innovations. Hundreds of millions of years Numbers of families
Adaptive radiation after the rise of key innovation. Example: the hypocone in mammalian cheek teeth: Evolved > 20 times independently during the last 65 Mio years. Groups with hypocone greatly diversified, groups without did not. The hypocone improves the processing of plant materials.