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Habitat Fragmentation

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  1. Habitat Fragmentation "Let's start indoors. Let's start by imagining a fine Persian carpet and a hunting knife. The carpet is twelve feet by eighteen, say. That gives us 216 square feet of continuous woven material. Is the knife razor sharp? If not, we hone it. We set about cutting the carpet into thirty-six equal pieces, total them up--and find that, lo, there's still nearly 216 square feet of recognizably carpet like stuff. But what does it amount to? Have we got thirty-six nice Persian throw rugs? No. All we're left with is three dozen ragged fragments, each one worthless and commencing to come apart." Quote from David Quammen’s (1996) Song of the Dodo; Image from www.floridahabitat.org

  2. Habitat Fragmentation Habitat fragmentation is an anthropogenic disturbance Disturbance – a discrete event that removes biomass (and thereby can create heterogeneity or “patchiness”) Photo of a fragmented Valdivian forest in Chile from: www.tncfire.org

  3. Habitat Fragmentation Habitat fragmentation is an anthropogenic disturbance with two components: (1) A reduction in area of the focal habitat type (2) A change in habitat configuration; remaining patches are smaller and more isolated than in the original configuration Photo of a fragmented Valdivian forest in Chile from: www.tncfire.org

  4. Nature is Inherently “Patchy” & Dynamic “Water, earth, and fire are Louisiana’s three special ingredients… The lowlands flood. The uplands burn… if you live in Louisiana, there are only two possibilities: either your land will eventually flood, or it will eventually burn. Most of our native plants and animals are therefore dependent on either flooding or fire or, in some cases, both.” Paul Keddy (b. 1953) Photo of Paul Keddy from www.drpaulkeddy.com; quote from Keddy’s (2008, pg. 14) Water, Earth, Fire

  5. Nature is Inherently “Patchy” & Dynamic Space-time Mosaic (Watt 1947); Shifting Mosaic (Bormann & Likens 1979); Patch Dynamics; Crazy Quilt (H. S. Horn) Natural disturbance regime Green = Eastern hemlock Purple = American beech Red = Red maple Yellow = Yellow birch 500 yr 1000 yr Images from Deutschman et al. (1997); www.sciencemag.org

  6. Nature is Inherently “Patchy” & Dynamic Nature is inherently “patchy,” but anthropogenic disturbanceoften results in landscapes different from (and potentially less hospitable than) those resulting from natural causes Natural disturbance regime Anthropogenic clearcut 500 yr 1000 yr Images from Deutschman et al. (1997); www.sciencemag.org

  7. Nature is Inherently “Patchy” & Dynamic Nature is inherently “patchy,” but anthropogenic disturbanceoften results in landscapes different from (and potentially less hospitable than) those resulting from natural causes Fragmentation reduces the extent and connectivity of habitats Fragmented landscapes typically have simplified internal structure of patches and matrices Fragmented landscapes typically have more contrast between adjacent patches (including patch-matrix juxtaposition) Features of fragmented landscapes (e.g., roads and dams) pose special threats to population viability

  8. Patch (Fragment) Size & Isolation Log10 (No. species) Log10 (Area) Data for Galapagos plants from van der Werff (1983) Vegetatio

  9. Patch (Fragment) Size & Isolation Data for Bismark Archipelago birds from Diamond (1972) PNAS

  10. Patch (Fragment) Size & Isolation Island Biogeography Theory emphasizes dynamism & patchiness of natural processes Conservation Biologists (and managers) must understand natural processes, to make sense of anthropogenic disturbances and to restore ecological / evolutionary processes Robert MacArthur(1930-1972) E. O. Wilson(b. 1929)

  11. Island Biogeography Theory Concerns the dynamics of immigration from a mainland source pool and extinction on islands or patches surrounded by inhospitable matrix Map on left from www.mapsofworld.com; map on right from www.peloncillo.org

  12. Island Biogeography Theory Why does the immigration rate decline as a function of S? Immigration rate (e.g., new species per yr) Number of species (S)

  13. Island Biogeography Theory Why does the extinction rate increase as a function of S? Extinction rate (e.g., number of species per yr) Number of species (S)

  14. Island Biogeography Theory Immigration rate (e.g., new species per yr) Turn-over rate (T) Extinction rate (e.g., number of species per yr) Equilibrium S Number of species (S)

  15. Island Biogeography Theory Why does the probability of immigration for each species vary with island isolation? Near island Immigration rate (e.g., new species per yr) Far island TNear TFar Extinction rate (e.g., number of species per yr) SFar SNear Number of species (S)

  16. Island Biogeography Theory Why does the probability of extinction for each species vary with island size? Small island Immigration rate (e.g., new species per yr) Large island TSmall TLarge Extinction rate (e.g., number of species per yr) SSmall SLarge Number of species (S)

  17. Island Biogeography Theory Near island Small island Immigration rate (e.g., new species per yr) Far island Large island Extinction rate (e.g., number of species per yr) SFar,Small SNear,Large SNear,SmallSFar,Large Number of species (S)

  18. Single Large or Several Small (SLOSS) Debate Ecological Assembly Rules E.g., Sometimes we find nested subsets in which larger areas contain the same subset of species as smaller areas, plus additional area-sensitive species Jared Diamond(b. 1937) From from Wikipedia

  19. Single Large or Several Small (SLOSS) Debate Nested Subsets A B A B C D E A B C Jared Diamond(b. 1937) Relaxation – loss of species that occurs after fragmentation event If fragments contain nested subsets of species, then a single large reserve is better than several small ones of the same total area (SLOSS debate) From from Wikipedia

  20. Species Especially Vulnerable to Fragmentation Wide-ranging Poor dispersal abilities Specialized requirements Low fecundity Vulnerable to human exploitation or persecution Cougar Arctic tern Desert pup fish Coyote Ground nut Heliconius erato Images from Wikipedia

  21. Lago Guri Islands, Venezuela Not just relaxation, but devastating ecological meltdown owing to top-down trophic cascades Perturbation that propagates downward through two or more trophic levels, resulting in alternating positive and negative impacts on successive levels John Terborgh(b. 1936) Photo from www.env.duke.edu

  22. Top-Down Trophic Cascades – + + + – – + + Tree seedlings Tree seedlings Photos from Wikipedia

  23. Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil Thomas Lovejoy Bill Laurance Recipients of the 2009 BBVA Foundation Frontiers of Knowledge Award in Ecology & Conservation Biology Photos from www.mongabay.com

  24. Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil Photo of a forest fragment, surrounded by newly created cattle pasture in Brazil

  25. Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil NASA false-color remotely sensed image of the confluence of Río Negro & Río Solimões (Amazon)

  26. Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil NASA false-color remotely sensed image of BDFFP

  27. Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil Edge effects – negative effects of a habitat edge on interior conditions Some species can only inhabit the interior or core, and some are specifically attracted to the edge Figure from Laurance et al. (2006) PNAS

  28. Corridors Corridors can help connect fragments a E.g., United Nations Educational, Scientific & Cultural Organization (UNESCO) World Heritage Sites in the Wet Tropics of Queensland, Australia Map from www.enviro-map.com

  29. Conservation Biologists (and managers) must understand natural processes, to determine conservation targets & how to achieve them Image from www.rewilding.org

  30. Conservation Biologists (and managers) must understand natural processes, to determine conservation targets & how to achieve them Image from www.rewilding.org