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In-Depth Information
Chapter 14
Ideas for Moving Beyond Structure to Dynamics of Ecological
Networks
Daniel B. Stouer, Miguel A. Fortuna and Jordi Bascompte
Integrative Ecology Group
Estacion Biologica de Donana, CSIC
C/Americo Vespucio s/n, E-41092 Sevilla, Spain
14.1. Introduction
There are between seven and fty million dierent species of plants and animals
on Earth [Pimm and Raven (2000)]. About two-thirds of these species live in the
tropics, largely in the tropical forests [Pimm and Raven (2000)]. In fact, studies
show that about 30{50% of plant, amphibian, reptile, mammal, and bird species
occur in 25 hotspots that occupy no more than 2% of the terrestrial land mass
[Myers et al. (2000)]. It is believed that sh and other marine organisms are similarly
concentrated [McAllister et al. (1994)].
The concentration of natural species demands that hotspots be managed with
particular attention and caution [Ceballos et al. (2005); Ceballos and Ehrlich (2006);
Hurlbert and Jetz (2007)]. Unfortunately only about one half of the original 16
million square kilometers of tropical rain forests remain [Skole and Tucker (1993)]
and clearing eliminates about 0.2 million square kilometers every year [Nepstad
et al. (1999); Cochrane et al. (1999); Hansen et al. (2008)]. This and other factors,
such as human population growth and global warming, place us in the midst of the
sixth largest extinction event in natural history [Thomas et al. (2004)].
The impacts are far reaching as extinctions of species represent one of the most
dramatic ecosystem perturbations, taking place on quicker time scales than evo-
lution and the introduction of new species into a habitat [Thomas et al. (2004)].
Extinctions have the ability to greatly alter an ecosystem's biodiversity; they can
aect ecosystem stability, its resilience to environmental change, or its resistance to
invasion of exotic species [Chapin et al. (2000)].
In the ocean, the story is no dierent. Currently 75% of global sh stocks
are fully- or over-exploited [United Nations Food and Agriculture Organization
(2006)]. Amongst these stocks are a considerable number of predators, such as
sharks, which occupy the highest trophic levels; it is observed that these species have
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