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." Note that the cut-up carpet metaphor is imperfect since habitat fragmentation necessarily entails both habitat reduction and change in habitat configuration. Quote from David Quammen’s (1996) Song of the Dodo; Image from www.floridahabitat.org

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

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

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

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 F. H. Bormann & G. E. Likens. 1979. Pattern and Process in a Forested Ecosystem. Springer, New York. D. H. Deutschman, S. A. Levin, C. Devine, & L. A. Buttel. 1997. Scaling from trees to forests: analysis of a complex simulation model; www.sciencemag.org/feature/data/deutschman/index.htm; advertised in: Science 277:1623. A. S. Watt. 1947. Pattern and process in the plant community. J. Ecol. 35:12-22. 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

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 Natural disturbance regime D. H. Deutschman, S. A. Levin, C. Devine, & L. A. Buttel. 1997. Scaling from trees to forests: analysis of a complex simulation model; www.sciencemag.org/feature/data/deutschman/index.htm; advertised in: Science 277:1623. Anthropogenic clearcut 500 yr 1000 yr Images from Deutschman et al. (1997); www.sciencemag.org

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 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

Patch (Fragment) Size & Isolation Log10 (No. species) van der Werff, Henk (1983) Species number, area and habitat diversity in the Galapagos Islands. Vegetatio 54:167-175. Log10 (Area) Data for Galapagos plants from van der Werff (1983) Vegetatio

Patch (Fragment) Size & Isolation Diamond (1972), who compared species richness on islands with that expected for an island “near” (< 500 km) a “mainland” source; “Mainland” = New Guinea; Islands = Bismark Archipelago. See: Jared Diamond. 1972. Biogeographic kinetics: Estimation of relaxation times for avifauna of southwest Pacific islands. PNAS 69:3199-3203. Data for Bismark Archipelago birds from Diamond (1972) PNAS

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 Joint consideration of area and distance led to the Equilibrium Theory of Island Biogeography (Munroe 1948; MacArthur & Wilson 1963, 1967; for a good description see Gotelli 2001, chapter 7). A key assumption of the model is that there is a permanent mainland source pool of species from which colonists are drawn. Robert MacArthur (1930-1972) E. O. Wilson (b. 1929)

Island Biogeography Theory Concerns the dynamics of immigration from a mainland source pool and extinction on islands or patches surrounded by inhospitable matrix Joint consideration of area and distance led to the Equilibrium Theory of Island Biogeography (Munroe 1948; MacArthur & Wilson 1963, 1967; for a good description see Gotelli 2001, chapter 7). A key assumption of the model is that there is a permanent mainland source pool of species from which colonists are drawn. Map on left from www.mapsofworld.com; map on right from www.peloncillo.org

Island Biogeography Theory Why does the immigration rate decline as a function of S? Immigration rate (e.g., new species per yr) Why does the immigration rate decline as a function of S? See pg. 21 MacArthur & Wilson (1967) For a given island, notice that the immigration rate must be zero at Smax (the total number of species in the mainland species pool). Number of species (S)

Island Biogeography Theory Why does the extinction rate increase as a function of S? Why does the extinction rate increase as a function of S? See pg. 22 MacArthur & Wilson (1967) For a given island, notice that there can be no extinctions when the number of species on the island is zero. Extinction rate (e.g., number of species per yr) Number of species (S)

Island Biogeography Theory Immigration rate (e.g., new species per yr) Turn-over rate (T) Notice that turn-over rate expressly quantifies dynamism, even at equilibrium for S. Extinction rate (e.g., number of species per yr) Equilibrium S Number of species (S)

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)

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 Note that for a given number of species already on the islands (i.e., the same number on each island), the probability that one species goes extinct is greater on a small island than on a large island. Extinction rate (e.g., number of species per yr) SSmall SLarge Number of species (S)

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,Small SFar,Large Number of species (S)

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) It’s relatively straightforward in the IBT framework to compare two islands or patches, but how does one compare one large island or patch with several small islands or patches? What about even more complicated comparisons? From from Wikipedia

Single Large or Several Small (SLOSS) Debate Nested Subsets A B A B C D E A B C Jared Diamond (b. 1937) It’s relatively straightforward in the IBT framework to compare two islands or patches, but how does one compare one large island or patch with several small islands or patches? What about even more complicated comparisons? In the cartoon in the slide, if the largest patch were fragmented into patches like the two smallest patches, species D & E would be lost – that’s what Diamond meant by “relaxation.” 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

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

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 See Case Study 7.3 in your textbook. Top carnivores are often especially area-sensitive, so are often among the first to be lost from fragmented landscapes. John Terborgh (b. 1936) Photo from www.env.duke.edu

Top-Down Trophic Cascades – + + + – + – + Solid arrows = direct effects; dashed arrows = indirect effects Tree seedlings Tree seedlings Photos from Wikipedia

Biological Dynamics of Forest Fragments Project (BDFFP), Amazonas, Brazil Inaugural BBVA Foundation Frontiers of Knowledge Award in Ecology and Conservation Biology recipients in 2009. T. Lovejoy was one of G. E. Hutchison’s last Ph.D. students (see N. Slack biography of Hutchinson). Thomas Lovejoy Bill Laurance Recipients of the 2009 BBVA Foundation Frontiers of Knowledge Award in Ecology & Conservation Biology Photos from www.mongabay.com

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

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

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

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 Here, we used a strategic, stratified set of 40 of the BDFFP’s 66 1-ha study plots… Laurance, William F., Henrique E. M. Nascimento, Susan G. Laurance, Ana Andrade, José E. L. S. Ribeiro, Juan Pablo Giraldo, Thomas E. Lovejoy, Richard Condit, Jerome Chave, Kyle E. Harms & Sammya D’Angelo. 2006. Rapid decay of tree-community composition in Amazonian forest fragments. Proceedings of the National Academy of Sciences 103:19010-19014. Figure from Laurance et al. (2006) PNAS 27

Corridors can help connect fragments 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

Conservation Biologists (and managers) must understand natural processes, to determine conservation targets & how to achieve them An example general recommendation by one NGO. Image from www.rewilding.org

Conservation Biologists (and managers) must understand natural processes, to determine conservation targets & how to achieve them An example general recommendation by one NGO. Image from www.rewilding.org