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The Biodiversity Crisis – WHAT’S CAUSING IT??? Part 1

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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 impacts Habitat Alteration Destruction Fragmentation Degradation Overexploitation of species

2 I. Human Impacts – Population growth correlated to biodiversity crisis
Endemic Bird Areas and Centers of Plant Diversity in Forests I. Human Impacts – Population growth correlated to biodiversity crisis


4 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.

5 II. Habitat alteration

6 A. Habitat destruction Deforestation - GOING, GOING GONE?
150,000 – 210,000 km2 lost per year


8 B. Habitat Fragmentation

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 things Where 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 smaller Filtering hypothesis = reduction in the # of species during dispersal Stepping 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 area closely spaced habitat patches are better than widely spaced ones 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 connected patches are better than unconnected patches a circular patch is better than a noncircular patch

15 2. Fragmentation = Formerly continuous natural habitats broken up due to the encroachment of civilization 2 components of habitat fragmentation:

16 Habitat fragmentation affects patch size, quality & connectivity

17 A constellation of separate habitat patches may be critical to the survival of individuals or populations

18 Biological consequences of fragmentation
Initial exclusion Crowding effect Insularization and area effects Isolation Edge effects Matrix effects Road problems Species invasions Ecological processes


20 Natural edge areas are important
Inherent edges are usually long-lasting features of the landscape related to: Topographic differences Soil type shifts Presence of open water Or 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 edges Alter patterns of local diversity Population dynamics

23 Edge effects can cause some species to thrive, whereas others perish -
2 Brown-headed Cowbird eggs in a Blue-winged Warbler's nest 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. 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 edge Edge habitat Core habitat -


26 Review: Fragmentation Results in
-isolated fragments - Edge effects: -alters microclimate -increase temp, decrease humidity

27 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

28 Iberian lynx, hunted to near extinction
Grizzly Bear – wide ranging, 70 to 400 square miles Green Sea turtle – low reproductive capacity, takes years Checkerspot butterfly – poor disperser, needs serpentine native grasslands

29 C. Habitat degradation

30 Acid precipitation, ozone depletion
NOx & Sox emissions HCl and ClONO2

31 4). Climate Change Greenhouse effect in full swing!
Reproduction cycles shifting: birds, frogs Alteration in vegetation composition


33 CO2 EMISSIONS BY SECTOR AND DEVELOPMENT: 1990-2003 in Scandinavia

34 III. Overexploitation of species
Commercial harvesting Bushmeat crisis Collectors

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