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the removal of a few predators will have a disproportionate effect on the dynamics
of prey populations. In short, assumptions of the ecological isolation of resource
extraction need to be interrogated.
In terms of impact on ecological relations, the ways in which resources are
extracted are often seen as relatively unimportant compared to the aggregate mag-
nitude of resource extraction. Under what situations (research question, land-use
ecology, and variation of extraction practices) is the manner in which resources are
extracted likely to be important in terms of impact on ecological productivity? By
'manner of resource extraction', I refer to the following: the spatial pattern of
extraction; the seasonality of extraction; the portion of ecological population that
is extracted (e.g., demographic cohort or development stage of ecological popula-
tion); or the morphological parts of the organism extracted (e.g., roots, leaves, stem,
fruits, seeds of plants; horn, hair, wool, body . . . etc of animals).
Over a wide range of extraction pressures, how a resource is extracted may have
more important effects on ecological relations than the aggregate level of extrac-
tion. This may be true not only due to variable sensitivities to the manner of
extraction of the biological populations from which resources are extracted but
also due to the indirect effects of resource extraction on broader biophysical systems
and biological populations not directly the focus of extractive pressure. An impor-
tant example of the former is that of the ecological effects of livestock grazing. On
the annual grasslands of Sahelian West Africa, where livestock husbandry retains
certain levels of mobility, how animals are grazed is more important than the
aggregate stocking rate at spatial scales ranging from a village territory to the whole
region. This results from: (i) grasslands are more sensitive (in terms of productivity
and species composition) to the timing (duration and seasonality) of grazing than
to the aggregate level of animals stocked over a yearly cycle; and (ii) grazing man-
agement results in a wide variation in the magnitude and timing of grazing pres-
sures experienced from one grazing site to another. Grasslands are primarily
sensitive to grazing during the rainy season. Given the nature of soils and the many
'natural' factors leading to declines in grass cover during the dry season, grazing
by domestic livestock during the dry season has limited effect. In such a system,
one needs to not only understand the factors that contribute to grazing manage-
ment variability but also the details of ecological response to grazing during the
rainy season. For example, defoliation experiments have found that short-term
response to grazing varies in magnitude and direction during the period of active
vegetative growth. In these experiments, simulated grazing bouts 2-3 weeks apart
produce the most positive and negative responses to grazing on same-year
productivity.
In sum, greater engagements with ecological relations are required to understand
social/ecological change when ecological features of interest display non-linear,
heterogeneous ecological responses to variation in how resources are extracted.
Heterogeneous response may work at the individual to population levels. At the
level of the individual organism, heterogeneous response is most common when
extracting resources from living organisms (lopping of trees, grazing of vegetation,
harvesting of fruits . . . etc.). At the level of the population, more complex response
patterns are most common where strong dependencies exist between the extracted
organism and others (e.g., fi gure 12.2). For those studying social-environmental
change, serious consideration of land-use ecology is important in evaluating the
appropriate level of engagement with ecological relations.
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