balance and the hydrological system, including water run-off and freshwater
courses and reservoirs. Moreover, poorly structured soils make these gradients more
dependent on the chemical and physical properties of bedrock, thereby enhancing
the role of this source of environmental heterogeneity. Overall, high mountains tend
to offer significant environmental heterogeneity (i.e. microhabitats) in combination
with strong seasonal fluctuations. In fact, to some extent this heterogeneity associated with steep gradients counterbalances isolation, favouring the existence of
altitudinal corridors and stepping stone routes that allow dispersal. The result is that
we expect relatively low levels of biodiversity, although this is highly idiosyncratic
and has a substantial spatial turnover.
All three ecological characteristics (isolation, harsh environment, steep environmental gradients) are the consequences of mountain topography and they
interact mutually. Strong environmental changes over small distances, together with
harsh abiotic conditions, may constrain a population’s expansion by limiting its
size, but they may also permit effective dispersal by saving relatively close barriers
or allow populations to migrate across the altitudinal range in search of suitable
conditions. Harsh conditions, in their turn, are a major component of pronounced
gradients—in fact, mountains tend to correspond to the extremes of many abiotic
gradients at the regional level—and they contribute to isolation (Fig. 2.1).
2.3 Conservation, Vulnerability and Trade-offs
One major goal of conservation is to deal with the vulnerability of natural systems
(species, populations, habitats, ecosystems) in the face of risks associated with
human activity, by maintaining or increasing the values related to the persistent
functioning of such systems. The concept of vulnerability may be approached from
different perspectives; in the ecological context, and particularly when assessing
climate change vulnerability is defined as the degree to which a system is able to
cope with adverse effects, being a function of (1) the exposure of the system in
question to agents that can potentially diminish these values, (2) the system’s
sensitivity to subsequent changes, and (3) its eventual resilience or adaptability to
the new context (Turner et al. 2003; Parry et al. 2007; Chapin et al. 2010). Let us
concentrate on the two first components, exposure and sensitivity, which are
affected by the immediate impact of environmental hazards: any situation involving
an increase in exposure or sensitivity will result in greater vulnerability and should
thus require conservation action. Similarly, conservation management could
maintain a given degree of vulnerability by reducing exposure when sensitivity is
increased (e.g. because populations become too small). Therefore, as a first
approach vulnerability would result from the product of exposure and sensitivity.
Given that vulnerability is defined in relation to a disruptive agent, if no such agent
exists, exposure and vulnerability equal zero.
The ecological characteristics of high mountain ecosystems have different
consequences on vulnerability (Fig. 2.1). Isolation reduces exposure to human
40
F. Lloret
courses and reservoirs. Moreover, poorly structured soils make these gradients more
dependent on the chemical and physical properties of bedrock, thereby enhancing
the role of this source of environmental heterogeneity. Overall, high mountains tend
to offer significant environmental heterogeneity (i.e. microhabitats) in combination
with strong seasonal fluctuations. In fact, to some extent this heterogeneity associated with steep gradients counterbalances isolation, favouring the existence of
altitudinal corridors and stepping stone routes that allow dispersal. The result is that
we expect relatively low levels of biodiversity, although this is highly idiosyncratic
and has a substantial spatial turnover.
All three ecological characteristics (isolation, harsh environment, steep environmental gradients) are the consequences of mountain topography and they
interact mutually. Strong environmental changes over small distances, together with
harsh abiotic conditions, may constrain a population’s expansion by limiting its
size, but they may also permit effective dispersal by saving relatively close barriers
or allow populations to migrate across the altitudinal range in search of suitable
conditions. Harsh conditions, in their turn, are a major component of pronounced
gradients—in fact, mountains tend to correspond to the extremes of many abiotic
gradients at the regional level—and they contribute to isolation (Fig. 2.1).
2.3 Conservation, Vulnerability and Trade-offs
One major goal of conservation is to deal with the vulnerability of natural systems
(species, populations, habitats, ecosystems) in the face of risks associated with
human activity, by maintaining or increasing the values related to the persistent
functioning of such systems. The concept of vulnerability may be approached from
different perspectives; in the ecological context, and particularly when assessing
climate change vulnerability is defined as the degree to which a system is able to
cope with adverse effects, being a function of (1) the exposure of the system in
question to agents that can potentially diminish these values, (2) the system’s
sensitivity to subsequent changes, and (3) its eventual resilience or adaptability to
the new context (Turner et al. 2003; Parry et al. 2007; Chapin et al. 2010). Let us
concentrate on the two first components, exposure and sensitivity, which are
affected by the immediate impact of environmental hazards: any situation involving
an increase in exposure or sensitivity will result in greater vulnerability and should
thus require conservation action. Similarly, conservation management could
maintain a given degree of vulnerability by reducing exposure when sensitivity is
increased (e.g. because populations become too small). Therefore, as a first
approach vulnerability would result from the product of exposure and sensitivity.
Given that vulnerability is defined in relation to a disruptive agent, if no such agent
exists, exposure and vulnerability equal zero.
The ecological characteristics of high mountain ecosystems have different
consequences on vulnerability (Fig. 2.1). Isolation reduces exposure to human
40
F. Lloret