Linking Habitat Restoration to Meaningful Units of Animal Demography

Abstract

To restore habitat is to restore the functional aspects of a place where one or more species are intended to live. However, habitat restored with the right structural elements can still fail to support the species due to insufficient space and spatial contiguity (e.g., movement corridors) with nearby habitat. The spatial extent of habitat determines its capacity to support various demographic units, such as a breeding pair of individuals, a true population, or a metapopulation. In scatter‐plots of published density estimates and their corresponding study area sizes, I found consistent patterns that appeared to represent spatial scale domains, in which subpopulations, populations, and multiple populations exist for each species. These spatial scale domains can help guide habitat restoration by indicating the minimum area needed to support a population. The effectiveness of restored habitat, considered alone or in combination with existing habitat, should be judged by the habitat's capacity to sustain a functioning population, which includes the population's membership in a metapopulation. Additionally, the evidence increasingly demonstrates that habitat must include sufficient space for the population(s) to periodically relocate as resources are depleted locally. The spatial extent of proposed habitat restoration can now be linked to the likely demographic unit of the species that can be supported there. I provide two examples of proposed habitat conservation and their likely effectiveness based on their spatial areas.

Seawalls do not sustain viable populations of limpets

“…On the other hand, where there have been studies of artificial structures, they tend to note whether abundances of animals are similar to those in natural habitats (Dickman & Doncaster 1987, Madejczyk et al 1998, Laakkonen et al 2001. When separated from demographic functionality, density may, however, lead to wrong conclusions about the value of artificial structures as alternative habitats, because they may just act as ecological sinks in which organisms fail to breed successfully (Smallwood 2001). Consequently, survival of populations in these artificial habitats will depend on immigration from other sources (Watkinson & Sutherland 1995).…”

Current conservation status of Ratites

“…Habitat restoration means to restore the functional aspects of a place where one or more species are intended to live (Smallwood 2001). However, recommendations regarding habitat restoration in conservation plans for small or declining populations as a means of increasing carrying capacity and lowering extinction risk are often made without assessing how much, if at all, habitat restoration would benefit the population.…”

The response of nuthatches (Sitta spp.) to restorative treatments in ponderosa pine ecosystems of northeastern Oregon.

“…Models with greater complexity than those presented here may capture more of the error inherent in each model. For example, density estimates alone without a measure of individual reproductive success or survivorship, fail to differentiate high-quality territories from ecological sinks that are attractive to low-quality or first-year breeding pairs (Smallwood 2001). An analysis of nesting abundance and success is necessary to determine whether the frequency of encounters of foraging individuals was due to foraging habitat alone, or nesting habitat differences between treatments.…”

“…Models with greater complexity than those presented here may capture more of the error inherent in the assumptions of each model taken separately. For example, density estimates alone without a measure of individual reproductive success or survivorship fails to differentiate high quality territories from ecological sinks that are attractive to low-quality or first-year breeding pairs (Smallwood 2001). …”

“…Density estimates alone without a measure of individual reproductive success or survivorship fails to differentiate high-quality territories from ecological sinks that are attractive to low-quality or first-year breeding pairs (Smallwood 2001). There was no difference in daily nest survival of Red-breasted Nuthatches in different treatment types (Table 3.2).…”