Terrestrial Reserve Design

I.  Conservation success is related to area conserved

    - One of ecology’s most consistent patterns is the relationship between area and species number
    - Habitat loss should reduce number of species in a consistent way
    - Spatial aspects of reserve design should be considered only after conserving the largest possible areas

A.  Case study -- Pimm and Askins (1995)

        – Does SAR predict extinction in eastern US?

            – Initially included 160 species in analysis, excluding species that occur only at the region’s margins, or are invasive

        – Assumed z = 0.25, 50% forest loss

            – Predicted 26 extinctions, an overestimate (4 actual), because:
                1.  Not all species required deciduous or coastal pine forest

                2.  Predicts local extinctions, not global extinctions

            – When they counted only species restricted to eastern US (28 species), 4/28 = 14% ~ 16% of species went extinct

B.  Extinction debt refers to the idea that past and current global changes may have condemned species to extinction that currently persist

C.  Source-sink dynamics (Pulliam 1988)

– Focus on habitat-specific demography
– In a source habitat, λ > 1
– In a sink habitat where λ < 1

1.  A sufficiently large source can maintain a huge area of sink

2.  Just because animal’s occupy a patch does not necessarily indicate quality habitat

3.  Restoration of sink can actually reduce metapopulation size

D.  Rosenzweig's species area relationships with extinction debt

E.  It is difficult to separate the effects of habitat loss from effects of fragmentation

II.  Fragmentation creates edge effects

A.  A brief history of edge effects in ecology

Phase 1
    - term popularized by Aldo Leopold “Game Management” (1933)

- suggested that "desirability of simultaneous access to more than one [habitat]"; and "the greater richness of [edge] vegetation" supported higher abundances of many species, and higher species richness

- a widely accepted “law of ecology” (Odum, 1958)

- led to management that maximized edge:area ratio

Phase 2
- habitat edges serve as the point of entry to interior habitats for many invasive or weedy species that have detrimental impacts on species of conservation interest

- new dichotomy "edge species" v. “interior species”

- new management outlook: edge effects are bad because they reduce the amount of habitat available to sensitive species of interior habitats

Example of Ecological Traps and Indigo Buntings

Phase 3
- human created edges should be minimized, but natural or semi-natural edges between reserve and matrix habitat can be created to improve habitat for native species

Making edge-effects predictive (Ries, et al. 2004)

III.  Edge and other landscape effects are intrinsically related to matrix effects
- At edges, bring in contact new resources and interactions
- Movement through matrix often important to spatial population dynamics

- Areas that are not part of the core network of protected areas are critical for conservation

        -- Countryside Biogeography
        -- Softening the matrix

IV.  Corridors

A.  To work, corridors must increase dispersal

       1.  Can behavioral assays be used to predict effects of corridors

B.  Corridors increase diversity of native species

       1.  Can be predicted by dispersal mode

       2.  Corridors effects can spill over into the matrix

C.  To function as intended: corridors must increase movement, may also provide habitat

D.  The negative effects of corridors:
    - They don't work for all species
    - They create edge effects

E.  Corridors do not spread invasives

F.  More work is needed to understand corridor effects on population persistence

G.  Other (tentative) corridor guidelines
- Corridors appear to be more effective when distances between patches are longer
- Beyond a certain point, increasing corridor width has little effect on colonization success
- Matrix key in determining corridor geometry
    - When movement rates through matrix are very low (<5%), benefits of corridors come through increased dispersal
    - When higher, benefits come through reduced matrix mortality