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Transcript
Evidence for species equilibrium Island Biogeography On an evolutionary scale, the equilibrium number of species results from the balance between rates of extinction and speciation 1. Survey of arthropods on small mangrove islands at different distances off Florida (determined species diversity) 2. Fumigated islands to kill all species 3. Re-censused islands for 2 years to look at colonization Island biogeography: the study of the abundance and diversity of species on islands, or “island like habitats (mountain tops, ponds, forest patches…) The theory of island biogeography: On an ecological scale, the equilibrium number of species results from the balance between rates of colonization and local extinction (depends on the # of species present) Evidence for species equilibrium The equilibrium theory of island biogeography 1. The number of species accumulates quickly and then tapers off 2. The equilibrium number of species is similar to the original values for each island 3. The species are turning over (changing) although the number of species stays the same 4. Why? Number of species present Predefaunation surveys The species equilibrium will be reached when rates of immigration match extinction species composition may change, but the number will stay the same Rates of immigration by new species will decline as the number of species already there increases (e.g. it is increasingly unlikely that a new colonist represents a new species for the island) Rates of extinction increase as the number of species on the island increases a) more species to go extinct b) competition and predation are likely to increase with increasing diversity The equilibrium theory of island biogeography The equilibrium theory of island biogeography Immigration and extinction curves vary as a function of island size and distance All mangrove islands were small, but the ones closest to the mainland had the highest equilibrium number of species Why would distance change the equilibrium number of species? Far islands will have slower colonization rates Small islands will have higher extinction rates 1 The equilibrium theory of island biogeography Tests of the equilibrium theory of island biogeography Immigration and extinction curves vary as a function of island size and distance small large Islands closer to Australia (the mainland source) have more species S S S S Tests of the equilibrium theory of island biogeography Application of island biogeography theory to conservation Habitats are becoming more and more fragmented (like islands) Can we manage so as to maximize diversity within these fragments? Islands in the East Indies: bigger islands have more species Park design assumptions: a) immigration will be minimal since unprotected areas surrounding parks will be destroyed minimal immigration b) Species equilibrium numbers will be driven by extinction Wooded habitats: larger fragments have more species conclusions: a) small parks will have higher extinction rates Application of island biogeography theory to conservation Habitat fragmentation Extinction rates in US National parks Small parks have : a) higher rates of extinction b) species with low populations are most vulnerable (predators, jaguars, wolves…) c) Extinction of predators can alter diversity of prey Park/Park Assemblage % loss of mammals Area (km2) Age (years) Bryce Canyon 36 144 61 Lassen Volcanic 43 426 77 Crater Lake 31 641 82 Manning Provincial 26 712 43 Mount Rainier 32 976 85 Rocky Mountain 31 1,049 69 Yosemite 25 2,083 94 Sequoia-Kings Canyon 23 3,389 94 Olympic 6 3,628 75 GlacierWaterton Lakes 7 4,627 82 Grand Canyon 18 4,931 76 Grand TetonYellowstone 4 10,328 84 Kootenay-BanffJasper-Yoho 0 20,736 85 Roads bring colonists who clear the land (Rondonia, Amazonian Brazil) Roads reduce biodiversity by: a) making barriers to dispersal (many organisms wont cross a road or even go near the edge of their habitat b) increasing colonization by weedy species and invasives 2 Park design : how can we minimize loss? better worse 1. Size Effects of connectivity (corridors) why? extinction less 2. Number Immigration more 3. Distance Immigration more 4. Connectivity (corridors) Immigration more Plant species diversity for patches of long leaf pine habitat that were unconnected or connected to other patches via corridors Park design : how can we minimize loss? Effects of connectivity (corridors) unconnected better Connected patches had higher diversity of native species (green bars) worse 1. Size why? extinction less But no difference for exotic species (yellow bars) connected At the beginning of the experiment, plants were removed and recolonized over time Edge effects: size and shape 2. Number Immigration more 3. Distance Immigration more 4. Connectivity (corridors) Immigration more 4. Shape Extinction less with less edge effects Effects of shape and amount of edge habitat Plant species diversity for patches that had lots of edges (winged) had lower species diversity than those with less edge effects (rectangular) 3 Minimum critical size project, Amazon, Brazil (size and edge effects) In partnership with cattle ranchers and loggers, created habitat islands of different sizes (1-100ha) and monitored changes in diversity rarity Smaller fragments lost diversity faster than bigger ones, but diversity in all fragment sizes declined dispersal ability Edge effects were enormous (changes in the abiotic environment near edges, such as increased light, drought stress, wind…) caused higher mortality and species loss diet specialization Characteristics of species that make them vulnerable to extinction trophic status Characteristics of species that make them vulnerable to extinction Conservation biology Understanding how to manage ecosystems to maximize preservation of biodiversity life span r (reproductive ability) 4