Presentation on theme: "The Biodiversity Crisis – WHAT’S CAUSING IT??? Part 1"— Presentation transcript:
1 The Biodiversity Crisis – WHAT’S CAUSING IT??? Part 1 Human impactsHabitat AlterationDestructionFragmentationDegradationOverexploitation of species
2 I. Human Impacts – Population growth correlated to biodiversity crisis Endemic Bird Areas and Centers of Plant Diversity in ForestsI. Human Impacts – Population growth correlated to biodiversity crisis
9 1. Island biogeography theory paved the way for understanding fragmentation effects Biogeography = the study of distributions of organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living thingsWhere do species occur, why do they occur there, and where are the greatest concentrations? Island theory:
11 I.B.T. applied to fragments – size matters - Probability of common forest interior neotropical migrant birds nesting in mid-Atlantic forests of various sizes
12 Hyperabundance phenomenon Animal populations “trapped” on small & medium sized islands have high population densities – WHY?Reduced competition?Reduced predation?
13 Predictions based on I.B.T. Compression hypothesis = on islands, as more species invade & are packed into the landscape, the niche occupied by each species becomes smallerFiltering hypothesis = reduction in the # of species during dispersalStepping stone hypothesis = smaller islands that lie between the main recipient island & its mainland colonizing source increase the rate of exchange
14 The I.B.T. & Conservation larger areas are better than smaller ones one large habitat area is better than several smaller ones of equal total areaclosely spaced habitat patches are better than widely spaced oneshabitat patches arranged at equal distances from one another are better than those arranged in a linear sequence of increasing distance from the first patch to the lastconnected patches are better than unconnected patchesa circular patch is better than a noncircular patch
15 2. Fragmentation = Formerly continuous natural habitats broken up due to the encroachment of civilization2 components of habitat fragmentation:
20 Natural edge areas are important Inherent edges are usually long-lasting features of the landscape related to:Topographic differencesSoil type shiftsPresence of open waterOr geomorphic factors (peaks, ridge-crests)
21 The problem with unnatural edges: Abrupt edges alter the microclimate conditions - resulting in changes in plant community composition, mortality rates, regeneration processes
22 Anthrophogenic fragmentation/edges Anthropogenic edgesAlter patterns of local diversityPopulation dynamics
23 Edge effects can cause some species to thrive, whereas others perish - 2 Brown-headed Cowbird eggs in a Blue-winged Warbler's nestDeforestation brought the cowbird into contact with naive populations of potential hosts, many of whom have not yet had time to evolve strategies for dealing with brood parasitism.Edge effects can cause some species to thrive, whereas others perish -
24 Edge habitat Core habitat - % of quail nests preyed upon as a function of distance from forest edgeEdge habitatCore habitat -
27 Species vulnerable to fragmentation Wide-ranging speciesNonvagile speciesSpecies w/specialized requirementsLarge-patch or interior speciesSpecies w/low fecundity or recruitmentSpecies vulnerable to exploitation
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