Objectives Conservation approaches: populations/species entire habitats Conservation biology relates to landscape ecology Habitat destruction/fragmentation causes much extinction Plans for preserves Size, number, shape, step stones, corridors Preserve community structure
Conservation Planning: Approach 2 Preserve habitats/areas, especially ‘biodiversity hotspots’ high species number high endemism
Endemic species: restricted to small geographic area; especially prominent on islands
Species richness Little spatial relation between species richness, threatened species, and endemic species Threatened species Endemic species
Deterministic causesof extinctions:the ‘evil quartet’ 1 habitat destruction and fragmentation (67% of cases) 2 introduced species 3 overkill (overexploit) 4 chains of extinction
Species introductions (e.g. this predatory snail) can eliminate native species.
Decline in marine organisms and increase in eutrophication due tohuman cultural development
Whalers shifted to new, less profitable species as populations of heavily hunted species declined.
Habitat reduction and elimination Some habitats are eliminated altogether. Fragmentation causes other problems: reduced total area reduced habitat heterogeneity reduced connectivity greater inter-fragment distance unable to migrate with changing climate reduced interior/edge ratio
Principles for design of nature preserves:If create preserve from large expanse of uniform habitat: larger is better than smaller SLOSS: single large or several small? one large area is better than several small that sum to same size add corridors or ‘stepping stones’ circular is better than elongate with more edge
Which size of area is needed? Will a park be Sufficient?
Why are larger areas better? support more species by reducing likelihood of stochastic extinction promote genetic diversity buffer populations against disturbance avoid ‘edge effects’ offer freedom to migrate
***Summarize two major results.Corridors enhance migration between patches and maintain population cohesion. Figure 3
***What are advantages of corridors? Increase immigration increase species richness provide a ‘rescue effect’ prevent inbreeding; add genetic diversity Increase foraging area for widespread species Provide cover for escape from predator when moving Alternative refuges from large disturbances Mix of habitats for species requiring them Are there disadvantages?
If creating preserve out of diverse habitat: Several small in different habitats better than one large in uniform habitat Plan for migration ---> use corridors stepping stones to link habitats bridge roads and pipelines that impede movement
Consider community structure Top-down control of trophic abundances Cascade effects: indirect effects extended through multiple levels Can have chain of extinctions if highly dependent Keystone organisms must be preserved Non-redundant species, key species that maintain stability/diversity
***What are conservation implications of the two contrasting models? Rivet/redundancy Would focus be on community dynamics or single-species dynamics? In which model are keystone species important?
How does species (and functional diversity affect community response to disturbance?
Community Principles An increase in the structural diversity of vegetation increases species diversity. Disturbance may be necessary to maintain all diversity. When disturbed, greater diversity leads to greater stability. Full restoration of native plant communities sustains diverse animal populations. A high diversity of plant species assures a year- round food supply for the greatest diversity of wildlife. Species survival depends on maintaining minimum population levels (>500).
Sample exam ? You are asked to design a national park system for a tropical country. 1) How will the concept of ‘hot spots’ of diversity influence your choice of areas to conserve? You have defined your locations. What are 4 principles that you will consider in the next phase: their spatial design? What specific attributes of parks are needed to accommodate specific flora or fauna? What general criteria related to preserve size must be met to ensure long-term survival of species? (assume habitat requirements are met)
Population models assume: large size (> minimum viable population size); no variation in average birth and death rates. In reality, randomness affects populations, especially small ones: Catastrophe Variation in environment Stochastic (random sampling) processes Chance events may cause small populations to go extinct.
Probability of extinction increases over time; increases with smaller initial population size. Small populations are more likely to go extinct due to random fluctuation in population size. Figure 4
***Summarize the two main results. Provide a reason for each result. What traits enable a population to rescue asmall population from extinction? Figure 5
Rescue effect: Immigration from a large subpopulation can keep a declining subpopulation from inbreeding and going extinct. Can produce positive density-dependence: survival of subpopulations increases with more subpopulations.
Mainland-island model:Sourceprovides emigrants to sink. source sinks Figure 6
Spatial Principles Large areas sustain more species than small areas. Many small patches in an area will help sustain regional diversity. Patch shape is as important as size. Fragmentation of habitats, communities, and ecosystems reduces diversity. Isolated patches sustain fewer species than closely associated patches. Species diversity in patches connected by corridors > than for disconnected patches. A heterogeneous mosaic of community types sustains more species, including rare species. Ecotones support a variety of species from both communities & species specific to the ecotone.