Goal: to preserve and repatriate endanger species. Most the consequence of either:

1. overexploitation
2. habitat destruction
3. pollution

Focus has been on large obvious species such as cheetah, panda bears, whales, etc. Certainly important but loss of genetic diversity (species) is even more monumental for species with not conservation programs.

e.g. insects, plants, freshwater fish, etc.

all decreasing because of habitat destruction.

Conservation project began in earnest in the late ’60 and early 1970’s.

1. Programs in zoos – foster breeding programs to repatriate stocks and supply zoo animals.
2. Other approaches emphasized habitat preservation based on thorough knowledge of the ecology of the species – particularly, requirement for resources, mating systems dispersal, etc.
3. More recently – particularly past 10 years focus has been not only on habitat preservation but also on critical size of population to sustain long term survival: effects of inbreeding and genetic drift.

Conventional wisdom: populations must maintain reasonable level of genetic diversity to prevent extinction due to inability to adapt to changing environment.

This has become a major focus but is it really the most important concern?

Will return to this topic but first look at the traditional conservation approaches, i.e. strategies employed to conserve habitat.

Question: what should the size and shape of reguia be to preserve as many species as possible?

Community structure approach:

MacAuthur and Wilson 1967 seminal monograph entitled: Theory of Island Biogeography

Their interest was in explaining patterns of species diversity. They noted a positive relationship between area of an island and the number of species present.

• large area, more species
• islands have fewer species than mainland
• larger islands have more species than small islands

Island defined as: habitat isolated from a source of species pool – mountain top, island in the oceans, patches of isolated vegetation. Not simply part of larger continuous entity.

Does availability of habitats (i.e. habitat diversity) alone account for this phenomenon or is isolation also important.

McA &W model – island size and distance (from source population) are the parameters used to predict number of species. Species number present on island represents an equilibrium between rates of immigration and extinction.

For immigation: Fig.1

Mechanism: simply chance dispersal and immigration

Small and far less likely to get dispersers, large and near more likely.

For extinction: Fig. 2

Premise: small islands, small populations, more intra and interspecific competition, this is more likely to leads to extinctions, also small populations susceptible to chance demographic extinction.

Fig. 3 Combine figures 1 & 2

Theory predicts:

1. number of species on islands constant
2. not result of stasis but continuous turnover
3. large islands more species than smaller islands
4. species number should decline with increasing remoteness for origin population.

Prediction 2 is a test of distance/isolation vs habitat diversity alone (set by limited diversity of habitat then species turnover low, if by distnace/isolation then should see constant turnover).

Predictions 3&4 important for designing refugia.

Evidence: Simberloff and Wilson experiment on mangrove islands - high turnover & consistency in species number over time.

Wilcox found decrease in diversity with more isolation. Fig. 5

But we should note that smaller islands have less diverse habitats. Both diversity in habitat and remoteness have impact on determining number of species and changes in species diversity over time.

Evolutionary processes: - Some species arrive, become established and evolve at faster rate than turnover or gene flow. May eventually lead to resistance of subsequent invaders.

What is the application of this theory to conservation strategies?

Best possible world – large area with large population of all species, but what if not possible?

Need to think of islands a habitat surrounded by "ocean" of unsuitable habitat.

Island Biogeography Theory helps to design area but also still need to know the ecology of species in detail, particularly for migrating species, large mammals have home ranges, etc (attempt in central America to form north- south corridor).

From principles of island biogeography:

1. large reserves will support more species
2. area that is part of continuum, if isolated, will support fewer species in each isolated habitat or "island"

Question – one large reserve or many small reserves?

Many ® less susceptible to disturbance, disease, etc.

Large ® less likelihood of extinction but population could be decimated by disease.

Many ® would support a greater diversity of habitats.

Few ® more patches.

Shape of refugia ® all circular (Fig. 6)

Why?

1. Reduces area at edges of refugia – less loss by migration.
2. Decrease potential for creation of small islands
3. Practical reasons, more easily enclosed and protected by enforcement.

Shape not a prediction of Island Biogeography Theory ® idea of circular refuge comes from empirical work. Peninsula of equal area to circular island has fewer species.

Conservation science most recently concerned not only with establishing adequate refugia - i.e., appropriate size and shape to sustain populations but

Also concerned with population size. What size is necessary to maintain maximum genetic diversity?

Premise: low genetic diversity, limited ability to response to environmental variability and thus limits the ability of population to respond to changing environmental conditions – i.e. limits evolutionary response.

Example from Greater Pairie Chicken study 1998 Science