Transcript Slide 1

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:
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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
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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