Download Habitat Fragmentation and Its Impact on Biodiversity and more Slides Biology in PDF only on Docsity! 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." Docsity.com Disturbance – a discrete event that removes biomass (and thereby can create heterogeneity or “patchiness”) Habitat Fragmentation Habitat fragmentation is an anthropogenic disturbance Docsity.com 500 yr 1000 yr Images from Deutschman et al. (1997); www.sciencemag.org 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 Docsity.com 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 Docsity.com 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 Docsity.com 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? Docsity.com 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 Docsity.com Immigration rate (e.g., new species per yr) Extinction rate (e.g., number of species per yr) Near island Far island TNear SNear Number of species (S) SFar TFar Island Biogeography Theory Why does the probability of immigration for each species vary with island isolation? Docsity.com Ecological Assembly Rules From from Wikipedia 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 Docsity.com 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) Docsity.com 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 Docsity.com
