24
C. Moritz
peatedly, subject to population viability (e.g., Malhotra and Thorpe 1991; Reznick
et al. 1997; Llsos et al. 1997) and the same conclusion can be drawn from phylogenetic analysis of recent adaptive radiations (e.g., Givnish 1997; Llsos et al. 1998).
This leads to the conclusion that phenotypic diversity among populations is potentially replaceable, whereas the genetic diversity due to historical isolation is not.
Bearing the above in mind, what conservation strategy is appropriate to meet
our goal of protecting evolutionary processes and potential? I would suggest a
binary approach, wherein we first identify historically isolated sets of population
within a species (ESUs sensu Moritz 1994) and then seek to maximise the potential
for adaptive evolution within these. The latter would include, for example, ensuring that the areas managed for each ESU encompass heterogeneous landscapes or
environmental gradients relevant to phenotypic evolution and functional diversity
of the species concerned. The maintenance of population and metapopulation
viability and of functional landscapes (see the chapter by Harrison, this volume) is
integral to this strategy.
Finally, the weight given to the two dimensions of diversity may vary depending on context. An emphasis on historical isolation (ESUs) is most appropriate to
species undergoing gradual evolution in relatively stable systems (e.g. see below).
For lineages undergoing rapid adaptive radiation and speciation the historical axis
of diversity may be less important and that concerned with adaptation more so.
Insofar as selectively driven speciation can occur without total genetic isolation
(Rice and Hostert 1993; Grant 1998) and over short time periods (e.g. Meyer et al.
1990), we should not apply the ESU concept blindly, but rather consider the ecological features of the species and their environment that promote this process.
3 Extension from Species to Communities
Quite correctly, there are concerns that by focussing on individual ESUs within
individual species we are "fiddling while Rome burns". Realistically, government
policies mandate attention towards threatened species, but the real gains are to
made through a proactive approach to conservation at the level of landscapes and
ecosystems. This is being acknowledged increasingly in strategies for locating
nature reserves (e.g. Sattler 1994) and managing diversity in multiple use landscapes. Priorities for such efforts typically are determined by selecting areas that
optimise the representation of vegetation communities and species in the total set,
and there has been substantial progress in developing algorithms to achieve this
(Pressey et al. 1993, 1994; Lombard et al. 1997). The challenge now is to develop
concepts that permit consideration of genetic diversity and, more importantly, evolutionary processes in the management of landscapes.
The concept of ESUs can be extended to communities through comparative
analyses of phylogeography for species with similar dispersal capability and ecological requirements (Avise 1992; Moritz and Faith 1998). Through the analysis
of a few putative indicator taxa, typically species with low vagility, the aim is to
C. Moritz
peatedly, subject to population viability (e.g., Malhotra and Thorpe 1991; Reznick
et al. 1997; Llsos et al. 1997) and the same conclusion can be drawn from phylogenetic analysis of recent adaptive radiations (e.g., Givnish 1997; Llsos et al. 1998).
This leads to the conclusion that phenotypic diversity among populations is potentially replaceable, whereas the genetic diversity due to historical isolation is not.
Bearing the above in mind, what conservation strategy is appropriate to meet
our goal of protecting evolutionary processes and potential? I would suggest a
binary approach, wherein we first identify historically isolated sets of population
within a species (ESUs sensu Moritz 1994) and then seek to maximise the potential
for adaptive evolution within these. The latter would include, for example, ensuring that the areas managed for each ESU encompass heterogeneous landscapes or
environmental gradients relevant to phenotypic evolution and functional diversity
of the species concerned. The maintenance of population and metapopulation
viability and of functional landscapes (see the chapter by Harrison, this volume) is
integral to this strategy.
Finally, the weight given to the two dimensions of diversity may vary depending on context. An emphasis on historical isolation (ESUs) is most appropriate to
species undergoing gradual evolution in relatively stable systems (e.g. see below).
For lineages undergoing rapid adaptive radiation and speciation the historical axis
of diversity may be less important and that concerned with adaptation more so.
Insofar as selectively driven speciation can occur without total genetic isolation
(Rice and Hostert 1993; Grant 1998) and over short time periods (e.g. Meyer et al.
1990), we should not apply the ESU concept blindly, but rather consider the ecological features of the species and their environment that promote this process.
3 Extension from Species to Communities
Quite correctly, there are concerns that by focussing on individual ESUs within
individual species we are "fiddling while Rome burns". Realistically, government
policies mandate attention towards threatened species, but the real gains are to
made through a proactive approach to conservation at the level of landscapes and
ecosystems. This is being acknowledged increasingly in strategies for locating
nature reserves (e.g. Sattler 1994) and managing diversity in multiple use landscapes. Priorities for such efforts typically are determined by selecting areas that
optimise the representation of vegetation communities and species in the total set,
and there has been substantial progress in developing algorithms to achieve this
(Pressey et al. 1993, 1994; Lombard et al. 1997). The challenge now is to develop
concepts that permit consideration of genetic diversity and, more importantly, evolutionary processes in the management of landscapes.
The concept of ESUs can be extended to communities through comparative
analyses of phylogeography for species with similar dispersal capability and ecological requirements (Avise 1992; Moritz and Faith 1998). Through the analysis
of a few putative indicator taxa, typically species with low vagility, the aim is to