At the dawn of the 21st Century,
the population of greater Phoenix, Arizona, in the northern Sonoran
Desert was gaining steadily on that of Guadalajara, Jalisco,
in dry tropical Mexico. As of 2002, these were the 6th and 2nd
most populous cities in their respective countries, and each
had a population exceeding 2.5 million people. These are also
the regions in which many neotropical migratory species spend
their summers and winters, respectively. Three of the ten largest
urban areas on the migratory corridor in between had populations
at or exceeding a half-million people (see graph, below).
The image, above left, shows the
surface of the Earth at night, where the lights from cities and
towns are visible from space (the landmasses are visible as a
pale backdrop). Associated with each of these population centers
are land uses including agricultural and livestock production,
energy production, woodcutting and forestry, water supply development,
waste management, transportation, recreation, and tourism, all
of which may bring immediate or long-term, intensive or dispersed
impacts to migratory pollinator populations and the ecosystems
that support them.
Populations
of twelve major urban areas in the migratory corridor between
Guadalajara, Jalisco (Mexico) and metropolitan Phoenix, Arizona
(United States). Notes:
{1} {2} {3}
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Agricultural and urban development
are anthropogenic land cover change processes that consume land
area and, in so doing, can contribute to ecosystem change. Recent
movement toward government-sponsored, accelerated tourism development
around the perimeter of the Gulf of California may also bring
new, broad-based threats to the integrity of the entire migratory
corridor. Larger-scale economic factors, including trade between
these two countries, may drive policy and individual decision-making
that results directly or inadvertently in degradation of natural
resources.
Fragmentation of vegetation at a
landscape scale and extraction and depletion of natural resources
such as water and wood may impact habitat structural elements
such as shade, shelter, nest sites, and nest-building materials.
Alteration of surficial processes such as runoff and erosion,
and pollution of ecosystem reservoirs - air, water, soil - that
can travel beyond the developed area, may feed back to vegetation
health and productivity. Habitat fragmentation can increase the
effort necessary for creatures to find food and other resources,
and can inhibit gene flow when populations become isolated from
one another. Disturbances may also contribute to changes in biodiversity
and species abundance, and to the introduction and spread of
non-native species.
The case studies below use remote
sensing imagery to provide insight to patterns of land cover
change in parts of the migratory corridor, with attention to
the consequences for plant resources available to migratory species.
Case Studies:
References:
Barbier, E. B. & J.
C. Burgess. 1996. Economic analysis of deforestation in Mexico.
Environment and Development Economics 1: 203-239.
Hutto, R. L. 1989. The
effect of habitat alteration on migratory land birds in a West
Mexican tropical deciduous forest: A conservation perspective.
Conservation Biology 3 (2): 138-148.
Maass, J. M. 1995. Conversion
of tropical dry forest to pasture and agriculture. In Seasonally
Dry Tropical Forests, S. H. Bullock et al. (eds.), pp. 399-422.
Cambridge University Press, New York.
Medillin, R. A., M. Equihua,
& M. A. Amin. 2000. Bat diversity and abundance as indicators
of disturbance in neotropical rainforests. Conservation Biology
14 (6): 1666-1675.
Rathcke, B. J. & E.
S. Jules. 1993. Habitat fragmentation and plant-pollinator interactions.
Current Science 65: 273-277.
Notes:
{1} Greater Phoenix total
includes Phoenix, Tempe, Glendale, Scottsdale, Mesa, Chandler,
Peoria, Avondale, Gilbert, Surprise, and Apache Junction .
{2} Data for Los Mochis and Obregon (all years) and Arizona cities
(1990, 2000, 2002) : World Gazetteer < http://www.world-gazetteer.com/
> July 2002 .
{3} Data for all other
Mexico cities (1990 and 1995 only) : INEGI < http://www.inegi.gob.mx
>.
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Remote
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