Environmental Engineering Reference
In-Depth Information
various sources of mortality. Some species are very specialized in their require-
ments, while others are generalists. Species also vary in their competitiveness for
limited resources, their tolerance of physically stressful conditions or of environ-
mental disturbances. Different conceptual schemes link particular groups of traits
to particular kinds of environment (e.g. r / K and CSR schemes).
Species traits and restoration
Effective restoration needs to be based on knowledge of which species will do well.
By monitoring the results of grassland restoration attempts, ecologists have deter-
mined the species traits that are linked with greater probability of establishment -
including a generalist trait, good powers of colonization, the ability to grow
vegetatively and the longevity of the soil seed-bank. In a similar manner, the success
of certain forest restoration attempts has been linked to seed size, ability to compete
and shade tolerance.
Species traits and invasion success
The success of some invasive species has a strong element of predictability. Among
pine tree species, for example, successful invaders are those with small seeds, high
growth rates, a short interval between successive large seed crops and a short juve-
nile period. In the case of birds, on the other hand, the ability of young to feed
themselves, a large brain size (linked to behavioral adaptability) and a broad diet
help to predict invader success. For freshwater fi sh, a broad diet and a wide range
of physiological tolerance seem important. But exceptions to these 'rules' are common
and there are many cases where no relationships have been found. Commonly, the
best predictor of invasion success is previous success as an invader elsewhere.
Species traits and extinction risk
Conservation managers need to know if there are suites of species traits that 'protect'
native species in the face of extinction threats or, alternatively, that make them more
likely to succumb to the pressures. Again the answer varies among taxonomic
groups but some generalizations emerge. For many taxa it is the ecological special-
ists that seem more at risk, while those showing greater fl exibility (in terms of
physiological tolerance ranges or diet) often fare better. And a pattern that has
repeatedly emerged is that extinction risk tends to be highest for species with a large
body size.
The fi nal word
Carl (Section 3.1) t ake s some comfort from our increasing knowledge of the species
traits that predict invasion risk. ' I still feel bad about accidentally introducing some
harmful meadow fl owers in my commercial wild fl ower mixes, but such an event must
be a lot less likely now. ' Or is it?
Make a list of fi ve or more exotic herbaceous fl owering plants that have become
invasive in your area. What problems do they cause? How did they arrive? Check
out your national biosecurity precautions: do you consider that these have elimi-
nated the probability of arrival of further invasive fl owers?
References
Angermeier, P.L. (1995) Ecological attributes of extinction-prone species: loss of freshwater
fi shes of Virginia. Conservation Biology 9, 143 -158.
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