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Habitat Fragmentation Quote from David Quammen’s (1996) Song of the Dodo; Image from www.floridahabitat.org "Let's start indoors. Let's start by imagining.

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Presentation on theme: "Habitat Fragmentation Quote from David Quammen’s (1996) Song of the Dodo; Image from www.floridahabitat.org "Let's start indoors. Let's start by imagining."— Presentation transcript:

1 Habitat Fragmentation Quote from David Quammen’s (1996) Song of the Dodo; Image from "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."

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

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

4 Photo of Paul Keddy from quote from Keddy’s (2008, pg. 14) Water, Earth, Fire 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)

5 Images from Deutschman et al. (1997); Natural disturbance regime 500 yr1000 yr Green = Eastern hemlock Purple = American beech Red = Red maple Yellow = Yellow birch Nature is Inherently “Patchy” & Dynamic Space-time Mosaic (Watt 1947); Shifting Mosaic (Bormann & Likens 1979); Patch Dynamics; Crazy Quilt (H. S. Horn)

6 500 yr1000 yr Images from Deutschman et al. (1997); Natural disturbance regime Anthropogenic clearcut Nature is Inherently “Patchy” & Dynamic Nature is inherently “patchy,” but anthropogenic disturbance often results in landscapes different from (and potentially less hospitable than) those resulting from natural causes

7 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 Nature is Inherently “Patchy” & Dynamic Nature is inherently “patchy,” but anthropogenic disturbance often results in landscapes different from (and potentially less hospitable than) those resulting from natural causes

8 Data for Galapagos plants from van der Werff (1983) Vegetatio Log 10 (Area) Log 10 (No. species) Patch (Fragment) Size & Isolation

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

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

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

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

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

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

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

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

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

18 Ecological Assembly Rules From from Wikipedia Jared Diamond (b. 1937) 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 Single Large or Several Small (SLOSS) Debate

19 Nested Subsets From from Wikipedia Relaxation – loss of species that occurs after fragmentation event A B C D E A B A B C Single Large or Several Small (SLOSS) Debate Jared Diamond (b. 1937) 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)

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

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

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

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

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

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

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

27 Figure from Laurance et al. (2006) PNAS 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 Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil

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

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

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


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