Ecotones and Ecological Gradients - Ecological Systems - page 147

Several studies have found evidence that some species are diverging in ecotonal
regions, suggesting that transitional areas may serve as speciation centers. Recent
work has shown increased genetic and morphological diversity in ecotonal regions
compared with neighboring areas. Ecotonal populations often coincide with periph-
eral populations along a species range. Some researchers suggest that because
ecotones often hold marginal populations that depend on other parts of the range for
the maintenance of genetic diversity, they do not deserve much conservation interest.
Alternatively, in the face of global climate and environmental changes, it has also
been argued that ecotones deserve special conservation investment, potentially being
speciation and biodiversity hotspots that hold relatively resilient populations. This
entry will provide a short overview of the history of ecotone research, recent novel
findings in the area and the implications for future conservation, biodiversity, and
sustainability research.

Conceptual Framework

Ecotones are areas where ecological communities, ecosystems, or biotic regions
coincide. They often occur in areas of steep environmental transition, along envi-
ronmental gradients. In these transitional regions, the environment rapidly shifts
from one type to another based on abiotic (e.g., climatic) and/or biotic (e.g.,
community structure) factors [ 13 , 19 ]. The origin of the word “ecotone” is in the
Greek roots “oikos” (home) and “tonus” (tension). Many different definitions and
terms have been used in the literature to describe ecotones and areas of ecological
transition. These include boundary regions, borders, meeting zones, transitional
zones, tension zones, zones of intermingling, and zones of transgression [ 19 ]. The
definition often contrasts ecotones with more homogenous areas found on both
sides of the transition or to the landscape as a whole. Ecotones can occur in both
terrestrial and aquatic systems, and cover several spatial scales, from large spatial-
scale ecotones, where biomes meet [ 40 ] to local-scale transitions, such as mountain
treelines ([ 11 ]; see Fig. 9.1 ). These areas are sometimes considered to be dynamic
zones of interaction between communities, which are unstable over time [ 19 ]. As
suggested by Odum [ 30 ], Ecotones do not simply represent a boundary or an edge;
the concept of an ecotone assumes the existence of active interaction between two
or more ecosystems with properties that do not exist in either of the adjacent
ecosystems. Ecotonal regions show a diversity of transitions that range from natural
transitions (e.g., altitudinal and latitudinal transitions) to human-generated
ecotones, sometimes termed anthropogenic ecotones (e.g., forest clear-cut edges
or urban ecotones) [ 24 ], as shown in Fig. 9.1 .

History of Research on Ecotones and Biodiversity

For over 100 years, since the late nineteenth century, there has been scientific
interest in boundary regions and edges of ecological systems. A conceptual