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The Biodiversity Crisis – WHAT’S CAUSING IT??? Part 1 I. II. Human impacts Habitat Alteration A. B. C. II. Destruction Fragmentation Degradation Overexploitation of species Endemic Bird Areas and Centers of Plant Diversity in Forests I. Human Impacts – Population growth correlated to biodiversity crisis From a sustainability perspective, when humanity's Footprint exceeds the amount of renewable biocapacity a draw down in natural capital is required and this is considered unsustainable. http://www.earthday.net/footprint/index_reset.a sp?pid=8696863066519484 II. Habitat alteration A. Habitat destruction Deforestation - GOING, GOING GONE? • 150,000 – 210,000 km2 lost per year B. Habitat Fragmentation 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 things – Where do species occur, why do they occur there, and where are the greatest concentrations? • Island theory: I.B.T. applied to fragments – size matters - Probability of common forest interior neotropical migrant birds nesting in mid-Atlantic forests of various sizes Hyperabundance phenomenon • Animal populations “trapped” on small & medium sized islands have high population densities – WHY? – Reduced competition? – Reduced predation? Predictions based on I.B.T. 1) Compression hypothesis = on islands, as more species invade & are packed into the landscape, the niche occupied by each species becomes smaller 2) Filtering hypothesis = reduction in the # of species during dispersal 3) Stepping stone hypothesis = smaller islands that lie between the main recipient island & its mainland colonizing source increase the rate of exchange The I.B.T. & Conservation 1. larger areas are better than smaller ones 2. one large habitat area is better than several smaller ones of equal total area 3. closely spaced habitat patches are better than widely spaced ones 4. habitat 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 last 5. connected patches are better than unconnected patches 6. a circular patch is better than a noncircular patch 2. Fragmentation = Formerly continuous natural habitats broken up due to the encroachment of civilization 2 components of habitat fragmentation: Habitat fragmentation affects patch size, quality & connectivity A constellation of separate habitat patches may be critical to the survival of individuals or populations Biological consequences of fragmentation Initial exclusion Crowding effect Insularization and area effects Isolation Edge effects Matrix effects Road problems Species invasions Ecological processes Natural edge areas are important • Inherent edges are usually longlasting features of the landscape related to: – – – – Topographic differences Soil type shifts Presence of open water Or geomorphic factors (peaks, ridge-crests) The problem with unnatural edges: • Abrupt edges alter the microclimate conditions - resulting in changes in plant community composition, mortality rates, regeneration processes Anthrophogenic fragmentation/edges • Anthropogenic edges – Alter patterns of local diversity – Population dynamics 2 Brown-headed Cowbird eggs in a Blue-winged Warbler's nest Edge effects can cause some species to thrive, whereas others perish - Deforestation 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. % of quail nests preyed upon as a function of distance from forest edge Edge habitat Core habitat - Review: Fragmentation Results in -isolated fragments - Edge effects: -alters microclimate -increase temp, decrease humidity Species vulnerable to fragmentation • • • • • • Wide-ranging species Nonvagile species Species w/specialized requirements Large-patch or interior species Species w/low fecundity or recruitment Species vulnerable to exploitation Iberian lynx, hunted to near extinction Checkerspot butterfly – poor disperser, needs serpentine native grasslands Grizzly Bear – wide ranging, 70 to 400 square miles Green Sea turtle – low reproductive capacity, takes 20-50 years C. Habitat degradation Acid precipitation, ozone depletion • NOx & Sox emissions • HCl and ClONO2 4). Climate Change • Greenhouse effect in full swing! • Reproduction cycles shifting: birds, frogs • Alteration in vegetation composition CO2 EMISSIONS BY SECTOR AND DEVELOPMENT: 1990-2003 in Scandinavia III. Overexploitation of species A. Commercial harvesting B. Bushmeat crisis C. Collectors