Environmental Engineering Reference
In-Depth Information
Synergetic Forces
Given the changes humans have made to the planet, many more factors
than climate change are affecting species (Laurance and Useche, 2009).
These include such things as land-use change, invasive species, introduced
chemicals, and hunting. Additionally, changes to a system can feedback on
other systems, which in turn may cause species more stress, for example, loss
of coastal marshes causing increased erosion. Managers have been work-
ing for decades to help species combat stresses, for example, by setting up
refuges for ducks where they are provided artificial lakes, food, and hunting
protection. Coping with one or even two of these stresses can be difficult
for species, but now adding the ubiquitous stress of a changing climate has
managers and others concerned about possible population declines, and in
extreme cases, extinction.
Certain traits can make a species more prone to extinction. These in-
clude the size of the species population (large population size is much more
stable than a small size); the size of the range of the species (a species with
a larger range size is less likely to become rare and then extinct); and spe-
cies that specialize on a particular trait, such as a particular prey item or a
particular tree for nesting. In the last case, such dependent species are at
greater risk of extinction due to their reliance on a particular item that could
itself be negatively changed by climate change. Such change can actually
cause a cascade of changes through the species communities due to the
interconnectedness experienced by species within an ecosystem.
Extinction
The average lifespan of a plant or animal species is ~7 million years,
which is the number of years a species persists from when the species arises
via speciation to when it goes extinct (Lawton and May, 1995). The best
estimate of how many plants and animals are extant compared to all plants
and animals that have ever existed is around 2%. Consequently extinction
is certainly a normal occurrence. The background level of extinctions (not
human induced) differs with different taxa and types of species. In ma-
rine species it is estimated to be ~0.1 to 1 Extinction per Million Species
Years (E/MSY). The number for mammals is similar, being ~0.2-0.5 E/MSY
(Foote, 1997; Alroy, 1998; Regan et al., 2001; MEA, 2005; May, 2010).
Determining historic extinction rates is difficult because of the time it
takes for a species committed to extinction—extinction will occur without
some major change occurring, such as human management—to reach the
point when we can document that the individuals in the population are no
