Geoscience Reference
In-Depth Information
biodiversity conservation. This type of analysis is often associated with the wide-
spread and still expanding approaches of 'conservation biology' and 'conservation
ecology', along with several highly cited scientifi c journals, including
Biodiversity
and Conservation
,
Conservation Ecology
,
Conservation Biology
, and
Diversity and
Distributions
.
Species richness (i.e., the number of species) estimated per unit area is an approxi-
mation of the extent of biodiversity that is highly useful. Species-level estimation is
often used alongside ones of other taxonomic levels at either the same or different
scales (e.g., within-species diversity, ecosystem-level diversity). Combined with bio-
geographic analysis, studies are able to identify areal concentrations and spatially
underrepresented areas (e.g., various forms of 'gap analysis'), while it also demar-
cates the areas of concentrated biodiversity (e.g., the concept of biodiversity 'hot
spots'). Noteworthy too are the occasional pro-conservation arguments that oppose
the logic of biodiversity 'hot spots' as the grounds for baseline conservation priori-
ties. This latter logic, while scientifi cally sound, widely accepted, and persuasive for
policy purposes, may overlook methodological differences as well as create philo-
sophical and political concerns about too narrow or one-dimensional a view of
biodiversity.
Environmental processes underpin the patterning of biodiversity that is of interest
to biogeographers. The most well-known factors behind spatial patterning are those
of the geo-environment, such as landforms, soils, and climate, which operate at mul-
tiple spatio-temporal scales (e.g., Rosenzweig 2003). Environmental variation thus
contributes a primary dimension to the differentiation of biodiversity at a range of
taxonomic levels (e.g., species, intra-specifi c populations, multi-specifi c guilds).
Modelling approaches, such as ecologic niche modelling (ENM), can relate the
spatial patterning of biodiversity occurrences (typically species-level) across land-
scapes to raster GIS coverages. Biodiversity-differentiating factors also are often dis-
tinguishable as historical events at the time scale of geo-environmental time spans.
Innumerable such events have that led to both the increase of biodiversity (e.g.,
through the geographic differentiation of species or intra-specifi c populations) or the
decrease (e.g., through extinctions generated through processes that are either
human-infl uenced or entirely unrelated to humans) (Young et al., 2002). The latter
distinction draws the contrast between 'natural' or autogenic disturbances, as the
creation of tree fall gaps within forests as a result of such factors as windthrow or
pests), on the one hand, and anthropogenic disturbances, on the other hand. It is the
properties of scale, magnitude, and frequency that are used to determine the resem-
blance of these disturbance regimes (Zimmerer and Young, 1998; Botkin, 2000).
Biodiversity is also infl uenced through myriad ecological interactions within and
among groups of organisms ranging from communities to ecosystems; these interac-
tions are highly spatially dependent. Particular species play key roles in the biodi-
versity-support functions of various communities and ecosystems. The roles of the
so-called keystone species are documented in an expanding number of case studies
as well as modelling and theoretical treatments of biodiversity. One well-known
example of a keystone species is the California sea otter, which preys on sea urchins
and thus, indirectly, on the diverse kelp forests that are grazed by the sea urchins;
another example is nitrogen-fi xing bacteria in many soils environments (Ehrlich and
Levin, 1998). Geographic scale and spatial analysis are important to the ecological
perspective on biodiversity. For example, geographic scale infl uences the ecological
interactions of keystone species and thus the regulation of biodiversity-related
