Community Ecology 3: Species Diversity and Biogeography PDF

Community Ecology 3: species diversity and biogeography  Ecology in the news… Brainy guys get more chicks  Ecology in the news… Bowerbirds of Australia Need to know 1. Be able to describe the latitudinal gradient, and identify and understand three hypotheses for why this gradient exis...

Community Ecology 3: species diversity and biogeography  Ecology in the news… Brainy guys get more chicks  Ecology in the news… Bowerbirds of Australia Need to know 1. Be able to describe the latitudinal gradient, and identify and understand three hypotheses for why this gradient exists 2. Be able to describe and graph the island biogeography theory for species richness, and predict how island distance and size affect species richness 3. Be able to describe how the size of a habitat fragment affects the rate of species loss within that fragment over time. 4. Be able to describe how wildlife corridors can be implemented to increase connectivity of habitats to promote conservation.  Global Patterns in Biodiversity Species richness generally increases towards the equator The Latitudinal Gradient Why might this gradient exist?  Main Climatic Factors Associated with Biodiversity solar energy input and water availability 180 Species richness 160 200 Vertebrate species richness Tree species richness 140 100 120 (log scale) 100 50 80 60 40 20 10 0 1 500 1,000 1,500 2,000 100 300 500 700 900 1,100 Actual evapotranspiration (mm/yr) Potential evapotranspiration (mm/yr) (a) Trees (b) Vertebrates Evapotranspiration Evapotranspiration Some hypotheses 3 hypotheses about for this the pattern latitudinal gradient Rate%of%speciation Limit%for%how%many%species environment%can%contain think of this as a “carrying capacity”, but for species instead of individuals in a population Some hypotheses 3 hypotheses about for this the pattern latitudinal gradient Rate%of%speciation Limit%for%how%many%species environment%can%contain think of this as a “carrying capacity”, but for species instead of individuals in a population Some hypotheses 3 hypotheses about for this the pattern latitudinal gradient Rate%of%speciation Limit%for%how%many%species environment%can%contain think of this as a “carrying capacity”, but for species in community instead of individuals in a population Number of species limited by total resource availability Higher latitudes Tropics Ecological limits hypothesis Large land mass and lots of resources, thus large pop and lower extinction Photos: rates Wikimedia Commons Ecological limits hypothesis Photos: Wikimedia Commons Higher temp = increased physiol. rates and mutation Higher latitudes Tropics Evolutionary rates high mutation rates hypothesis High rate of speciation short generation times evidence from plants, mammals and amphibians Photos: Wikimedia Commons Recent glaciation = less time for speciation Higher latitudes More recent major disturbance (glacier cover) Last ice age ended 12,000 yrs ago Tropics History hypothesis Photos: Wikimedia Commons  learning catalytics In a huge (hypothetical) experiment, scientists found that if they watered and fertilized land at 30 degrees north for 50 years, species richness increased dramatically. This observation is consistent with which hypothesis about the latitudinal gradient in species richness? a. The evolutionary rates hypothesis b. The history hypothesis c. The ecological limits hypothesis d. This observation is not consistent with any of these hypotheses. e. This observation confirms all of these hypotheses. Area and Biodiversity  Area and Biodiversity Species-Area Curve shows, all else being equal: more area= more species Number of species Area (acres) How do we make sense of this relationship between area and species richness? MacArthur and Wilson’s Island Equilibrium Model (aka: theory of island biogeography) Species richness on islands is a balance between immigration and extinction Species richness on an “ecological island” levels off at some dynamic equilibrium point  Islands… Can be actual islands …or… Habitat islands Species richness is a balance of immigration and extinction RATE Number of species present Species richness is a balance of immigration and extinction Immigration rates decline as probability of NEW species arriving declines Total number of species on mainland =P note: ”mainland” is where species are immigrating from Species richness is a balance of immigration and extinction Extinction rates increase… Why? Species richness is a balance of immigration and extinction Extinction rates increase as: 1. Interspecific competition gets more intense 2. Average population sizes get smaller, increasing probability of chance extinctions. Species richness is a balance of immigration and extinction ⋀ S equilibrium species richness the predicted species richness for the island  Species richness is a balance of immigration and extinction Equilibrium rate of turnover Species “turnover” at equilibrium 2024 2034 2044  LC: When an island is at equilibrium for species richness A. Speciation and extinction rates = 0 B. No new species will arrive on the island C. No species on the island will go extinct D. Rates of species immigration and extinction are equal MacArthur and Wilson’s Island Equilibrium Model The immigration and extinction curves vary depending on whether islands are A. Small or large B. Near to mainland (source), or far from mainland (source) MacArthur and Wilson’s Island Biogeography Model small vs. large near vs. far MacArthur and Wilson’s Island Biogeography Model small vs. large near vs. far MacArthur and Wilson’s Island Biogeography Model near vs. far MacArthur and Wilson’s Island Biogeography Model rescue effect near vs. far Test of Island Biogeography Model Test of Island Biogeography Model near island intermediate islands far island Simberloff and Wilson 1970; Florida keys I don’t always LearningCatalytics. But when I do, I …uh…Learning catalytics True or false? Gator Island should have higher extinction rates than Louis Island.  Forest Fragment Project Habitat size also predicts rates of species loss  Golden Lion Tamarin Connecting fragmented Uniao Reserve landscapes open cattle pasture with Intact forest biological corridors requires identification of appropriate areas re-forested land Intact forest cheaper than buying huge land parcels Wildlife corridors come in all shapes and sizes, and can be vital to the persistence of species! corridors increase landscape connectivity See you Wednesday!