Ecological applications of niche theory - Ecological Applications: Toward a Sustainable World - page 52

species at the different sites where they occur). This variance is a measure of how
narrow (specialist) or broad (generalist) their niches are.
The fi rst of the two ordination axes corresponds to a gradient of soil conditions
from nutrient-enriched and moist (left) to nutrient-poor and dry (right) in 102 loca-
tions in southeast France (Figure 2.9a). The second axis corresponds to the mowing/
grazing management regime at these sites, from locations that are rarely mown and
lightly grazed (left) to sites that are heavily mown and very heavily grazed (right)
(Figure 2.9b).
Species restricted to very dry, nutrient-poor soils (to the extreme right in Figure
2.9a) had narrow niches along this axis (e.g. Aira caryophyllea and Tr ini a glauca ), in
contrast to the majority of species associated with intermediate fertility and water
availability (e.g. Thymus serpyllum and Festuca ovina ). The enr iched end of the spec-
trum favored species such as Lolium perenne and Bellis perennis . Species of highly
disturbed grassland (to the right in Figure 2.9b) tended to have narrow niches, with
high tolerance of trampling (e.g. Lolium perenne ), gra zing (e.g. Bombycylaena erecta )
or cutting disturbance (e.g. Aira caryophyllea ). Species associated with intermediate
mowing or grazing pressure had narrow or broad niches (e.g. Dianthus monspessu-
lanus and Eryngium campestre , respectively) and included several forbs with mor-
phological defenses to grazing (e.g. Eryngium campestre and Onionis spinosa ). Finally,
in the least disturbed part of the axis (to the left) were found species with narrow
(e.g. Chamaecytisus supinus ) or broad niches (e.g. Brachypodium pinnatum ) that can
only tolerate minimal grazing pressure or total absence of management. This infor-
mation can be used to defi ne adequate conservation management for the rarest
species, and particularly those with narrow niche breadths along both habitat and
management gradients. In addition, attempts to restore sustainable agricultural
regimes in particular areas will benefi t from this detailed knowledge about species
appropriate for introducing under the prevailing conditions.
There is a supreme irony in one ecologist working to restore a species in its native
range while another seeks its eradication in an invaded location. This is the case for
Hieracium pilosella (Figure 2.9a), an innocuous species with a broad niche that is
characteristic of intermediate fertility and water availability in European grassland.
In New Zealand, on the other hand, it is an aggressive invader that poses a heavy
economic burden to farmers and an equally heavy ecological cost to grassland bio-
diversity (Espie, 1994). The reasons for its success partly refl ect its broad fundamen-
tal niche, but in addition it is resistant to vertebrate grazing pressure and, moreover,
has arrived in New Zealand without its normal complement of natural enemies. In
its new home, in other words, it is not restricted to the relatively narrow realized
niche expressed in Europe.

2.4.3 How much
does it cost to restore
a species?

Another grassland study, with an interesting economic twist, was conducted by
Zechmeister et al. (2003) in 31 Austrian meadows. They found that specialist species
(w it h nar row niches in terms of soil moisture and nutrient concentrations) declined
in comparison to generalist species as agricultural practices intensifi ed (increased
fertilizer input and mowing). Moreover, the farmers' profi t margins were found to
correlate negatively with overall plant species richness, with meadows that provided
low or no profi t margins retaining highest species richness (Figure 2.10). This
emphasizes how biodiversity can be a matter of economics - the actual cost to the
farmer of preserving a single species was estimated to be between 150 and 200 euros.