Environmental Engineering Reference
In-Depth Information
affected [ 64 - 66 ]. A species in its native grounds may play no specific role in the
system, whereas an invasive species may have devastating effects in the system it
got introduced into, e.g., feral cats and rats on islands [ 67 ], Alewife ( Alosa
pseudoharengus ) in nonnative freshwater lakes and ponds [ 68 ], and Cheatgrass
( Bromus tectorum ) in nonnative grasslands [ 69 ].
Identifying keystone species therefore is not without its problems. It is also
important to notice that ecologically important species might not necessarily be the
ones that are also considered important by traditional conservationists (i.e., rare
species; [ 70 ]).
Issue-2: Usefulness for Management
Because of the limited resources available incomparisontoconservationneeds,it
has been proposed to design protection of single species in the aim of indirectly
protecting the regional biota. These “surrogate species” are roughly of three
categories [ 71 ]: (1) flagships, charismatic species that attract public support;
(2) umbrellas, species requiring such habitats that their protection might protect
other species; and (3) biodiversity indicators, taxa whose presence may indicate
high species richness. However the effectiveness of these policies has been
questioned and [ 70 ] suggested that single-species management might be more
effective when directed toward keystone species. Indeed, the importance of key-
stone species and ecosystem engineers in communities make these species partic-
ularly important conservation targets, since the loss of these species can affect
entire communities and ecosystems [ 72 ]. However, the main difficulty for apply-
ing these concepts to conservation issues laysonboththeidentificationofkeystone
species and ecosystem engineers in communities and on the context dependence of
their impacts, as discussed in the previous section. Thus, although these concepts
appear relevant for conservation policies, it is still a long way from providing
general and practical recommendations for conservationists and managers [ 71 ].
The concepts of keystone species and of ecosystem engineers could also be
useful for other management issues in natural and anthropized ecosystems, such as
for ecosystem restoration or agriculture. For example, in agro-ecosystems, several
well-known ecosystem engineers have been used to improve soil fertility and crop
yield. In some countries, farmers make use of the soil fertilizing effect of termites
by spreading termite mound soil in their field [ 73 ]. Similarly, earthworm inocula-
tion has generally positive effects on crop yield [ 74 ].
Future Directions
The notions of ecosystem engineers and keystone species have been playing
prominent roles in ecology for several decades, still many questions and
uncertainties ask for further investigations. Three of them are briefly described
here. The first
is how keystone roles and engineering effects are related to
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