BIO 360  Ecology

Lecture 20:  Spatial Ecology and Conservation

I.  Habitat loss and habitat fragmentation
    A.  As habitat is lost, what remains is typically separated into small patches that are isolated from one another
    B.  Spatially divided habitats are not caused only by humans, but can occur naturally in many situations

    C.  Important aspects of fragmentation
        1.  Local extinction refers to population loss within a fragment
        2.  Fragment area larger fragments tend to have larger populations
        3.  Fragment isolation nearby Fragments have higher population sizes

    D.  Consequences of habitat fragmentation -- small populations

II.  Conservation in fragmented landscapes
    1.  Corridors are thin strips of habitat that connect otherwise isolated areas and ideally increase population sizes and reduce local extinction

            -- Corridors increase butterfly movement
            -- Impact habitat-restricted species
            -- Increase population sizes
            -- Corridors increase seed dispersal
            -- Corridors increase pollinator movement
            -- See Figures 11.13 11.14

    4.  More generally, from the SRS Corridor Experiment and across other studies

      -- Corridor promote movement of habitat specialists

      -- Corridors increase plant diversity

      -- Effects may be positive or neutral; there have been few observations of negative effects

III.  Spatial population structure

    A.  Metapopulations
        1.  They are linked together by infrequent dispersal
        2.  Their population fluctuations are usually not synchronized

        3.  Models of metapopulation dynamics
             -- The change in the number of occupied patches is the difference between colonized and extinct patches

             p = proportion of occupied patches

             e = proportion of patches that become extinct

             c = proportion of patches that are colonized

             dp/dt = cp(1-p) - ep

            To determine the number of occupied patches at equilibrium:
             p = 1 - e/c

       4.  Note:  if populations become extinct, then all patches are not occupied

       5.  Conservation implication:  an unoccupied patch may be critical to maintain a population

       6.  St. Francis' satyr example

    B.  Source-sink populations
        1.  Source patches have lambda > 1
        2.  Sink patches have lambda < 1
        3.  Source patches maintain sink population through immigration
        4.  Implications: conserving occupied patches may not protect a species from extinction