Habitats, Processes
and Species at Risk
--From Nabhan, Gary Paul and Andrew R. Holdsworth.1998.
State of the Sonoran Desert Biome: Uniqueness, Biodiversity,
Threats and the Adequacy of Protection in the Sonoran Bioregion.
Sponsored by The Wildlands Project. p. 36
The field experts which we consulted identified as being
at risk many organisms, processes and habitats over and above
those which have been formally placed on endangered species
lists, on critical habitat inventories, and in red books.
Species at risk (see Appendix
4) will be treated in further discussions of each subregion,
but certain generalizations can be offered at this point:
1. Species vulnerable to competition from exotics are at
risk, especially endemic species with poor dispersal abilities
and specialized habitat requirements.
2. Species without adaptations to fire are at risk wherever
exotic grass plantings and invasions have increased fire frequencies
in their habitats.
3. Riparian and artesian spring habitats are at risk wherever
aquifer overdraft occur.
4. Riparian obligate species are at risk; the Merriam's pocket
mouse of mesquite bosque/riparian scrubland habitat has already
been extirpated, and -- riparian birds are rarer today than
a half century ago (Johnson et al. 1987).
5. Wildlife corridors for Neotropical migrants and between-mountain
range emigrants have become fragmented wherever urbanization,
agricultural conversion, water impoundment and canal construction
have become extensive.
6. Grasslands and their biota are at risk wherever the sowing
of exotic species is coupled with fire suppression, chaining
or intensive grazing during extended drought periods by high
densities of livestock (Bock and Bock 1992; Bahre 1991)
7. Coastal thomscrub endemics are at risk because of land
conversion to agriculture and livestock pasturage. The noted
Sonoran Desert botanist, Richard Felger, said that coastal
thornscrub is the single-most endangered major vegetation
community in the Sonoran Desert, if not the world.
8. Coastal wetland, sand strand and mangrove scrub communities
are at risk because of the narrowness of their habitat and
the alarming rate of coastal urbanization, dredging, aquaculture,
and recreational vehicle use.
9. Wildlife species now habituated to artificial water developments
are at risk wherever introduced diseases have been transmitted.
10. Native fish, otter, beaver and other aquatics remain
at risk wherever water impoundments, groundwater pumping and
/ or livestock grazing degrade their former habitats, favor
exotic species and / or substantially fragment their populations.
11. Island endemics are at risk wherever introduced livestock,
rats or cats have become established in their habitats.
12. Wherever carnivores have been depleted by hunting, trapping,
poisoning or habitat fragmentation, herbivorous mammal populations
may have increased to densities which radically change the
composition of vegetation, the regenerative capacity of certain
rare plants, and the periodicities of fire and other ecological
processes.
(Bock and Bock 1992;
Bahre 1991)
(Johnson et al. 1987).
Charles F. Wilkinson. Crossing the Next Meridian (1992)
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