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

I. Human impacts

II. Habitat AlterationA. Destruction

B. Fragmentation

C. Degradation

II. Overexploitation of species

Endemic Bird Areas and Centers of Plant Diversity in Forests

I. Human Impacts – Population growth correlated to biodiversity crisis

http://www.earthday.net/footprint/index_reset.asp?pid=8696863066519484

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.

II. Habitat alteration

A. Habitat destructionDeforestation - 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 ones2. one large habitat area is better than several

smaller ones of equal total area3. closely spaced habitat patches are better than

widely spaced ones4. 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 2. Fragmentation = Formerly continuous natural habitats broken up due to the encroachment of civilizationbroken 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 exclusionCrowding effect Insularization and area effects IsolationEdge effectsMatrix effectsRoad problemsSpecies invasionsEcological processes

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)

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

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.

2 Brown-headed Cowbird eggs in a

Blue-winged Warbler's nest

% of quail nests preyed upon as a function of distance from forest edge

Edge habitatCore 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

Checkerspot butterfly – poor disperser, needs serpentine native grasslands

Iberian lynx, hunted to near extinction

Green Sea turtle – low reproductive capacity, takes 20-50 years

Grizzly Bear – wide ranging, 70 to 400 square miles

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