1 MA Chap. 4: Biodiversity: Main Findings • Species in decline • The main causes of species extinction are changing from a historical trend of introductions and overexploitation affecting island species to present-day habitat loss and degradation affecting continental species. • While the vast majority of recorded extinctions since 1500 have occurred on oceanic islands, continental extinctions are now as common as island extinctions. Why are Island Species so sensitive? Proclivity to endangerment includes: • Isolation • Small numbers in geographically small areas • Lack of adaptations for coping with introduced (exotic) species (especially predators) • = Island Species!! MA Chap. 4: Biodiversity: Main Findings: Homogenization • Homogenization, the process whereby species assemblages become increasingly dominated by a small number of widespread, human-adapted species, represents further losses in biodiversity that are often missed when only considering changes in absolute numbers of species. • The many species that are declining as a result of human activities tend to be replaced by a much smaller number of expanding species that thrive in human altered environments. • Invasive species homogenization Anthropogenic homogenization Dams are classic examples of interventions in hydro regime that cause changes in ecology: downstream water quality and species diversity often changes.
Transcript
1
MA Chap. 4: Biodiversity: Main
Findings
• Species in decline
• The main causes of species extinction are changing from a historical trend of introductions and overexploitation affecting island species to present-day habitat loss and degradation affecting continental species.
• While the vast majority of recorded extinctions since 1500 have occurred on oceanic islands, continental extinctions are now as common as island extinctions.
Why are Island Species so
sensitive?
Proclivity to endangerment includes:
• Isolation
• Small numbers in geographically small
areas
• Lack of adaptations for coping with
introduced (exotic) species (especially
predators)
• = Island Species!!
MA Chap. 4: Biodiversity: Main
Findings: Homogenization
• Homogenization, the process whereby species
assemblages become increasingly dominated by
a small number of widespread, human-adapted
species, represents further losses in biodiversity
that are often missed when only considering
changes in absolute numbers of species.
• The many species that are declining as a result
of human activities tend to be replaced by a
much smaller number of expanding species that
thrive in human altered environments.
• Invasive species homogenization
Anthropogenic homogenization
Dams are classic examples of interventions in hydro regime that cause changes in
ecology: downstream water quality and species diversity often changes.
2
In the case of the dam shown earlier, Dutch John Dam on the Green River in
Utah, pre-dam conditions included warm, silt-laden water in which species like the
Pike Minnow (above) thrived. But the dam caused water temps to drop and
restricted the flow of sediment (which ends up in the reservoir), which created
conditions the Pike Minnow is not adapted to, but……
…trout, like this brown trout, do like the cold, clear water, and once introduced,
they take over the habitat. They are ”game” fish in the sense that people want to
catch them, and an economy of fishing developed around the trout which did not
exist for the less desirable pike minnow. (still, of course, the dam was not built to
purposefully create a sport fishery for university professors, that is an inadvertent
result).
MA Chap 4: Biodiversity
• Main messages
• 4.3: Anthropogenic Drivers
• (Skip this section: 4.4: Recent Trends in
Biodiversity)
• 4.6: Summary of Trends
MA Chap. 4: Biomes and changes
• The majority of biomes have been greatly
modified by humans. Between 20% and 50% of 9 of
the 14 biomes have been transformed to croplands.
Tropical dry forests are the most reduced by
cultivation, with almost half of the biome’s native
habitats replaced with cultivated lands. Three other
biomes—temperate grasslands, temperate broadleaf
forests, and Mediterranean forests—have
experienced 35% or more conversion. Biomes least
reduced by cultivation include deserts, boreal forests,
and tundra.
3
TMF: Trop and Sub-trop moist, broadleaf forests (tropical
rainforest)
TeG: Temperate grasslands
TG: Trop and Sub-trop Grassland, Savannahs, and Shrublands
T: Arctic or Alpine tundra
Habitat Change in the Biomes (MA
4.3): Fragmentation
• Fragmentation: “A major issue in habitat and land use change is habitat fragmentation…which leads previously continuous habitats to become divided.
• Conversion of habitat, and insertion of barriers (roads, etc.) creates habitat patches.
• Problem of “islands” emerges: biodiversity and pop inversely related to patch size.
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Habitat Fragmentation• Basic trends: habitat fragmented into smaller, further
apart “patches”—”shrink” intensified by “edge effect”(interior vs edge species).
• Remaining patches grow further apart, more isolated, individuals (plants and animals) increasingly can’t move among them.
• Fragments reside in a “matrix” of anthropogenic, disturbed habitat (farmland, subdivisions, etc)—often inhospitable to native species.
• Species change: those obligated to the remaining habitat patches decline, those able to move among patches and utilize the human-dominated matrix hold on.
• Especially: Generalist able to use patch, edge, and matrix increase (deer, raccoons, many weeds).
Fragmentation most easily observed
in forest habitat is caused by many
human activities (forestry, left, or
recreation, below), and it also occurs
in grasslands, savannah, wetlands,
riparian habitats, etc. Anywhere that
humans transformations cut up
continuous habitat.
Roads and other infrastructure fragment habitats by creating linear abrriers.
“Edge Effect” and edge vs. interior species.
We can mitigate the fragmenting effects of some barriers, like highways, by making
them more permeable—here an overpass north of Banff, Canada, is meant as a
way for bears to get from one side of the highway to the other.
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Summary of Biodiversity
Trends (MA Chap 4.6)• Current rates of species extinction are at least two orders of magnitude above background rates and are expected to rise to at least three orders above background rates—and they are increasing
• 20% of all species in those groups that have been comprehensively assessed (mammals, birds, amphibians, conifers, and cycads) are believed to be threatened with extinction in the near future. For birds (the only taxon for which enough data are available), this proportion has increased since 1988 (BirdLife 2004a). Even among species not threatened with extinction, the past 20–40 years have seen substantial declines in population size or the extent of range in most groups monitored.
• Second, changes are varied. Rates of biodiversity decline, although very largely negative, vary widely on at least three dimensions. Taxonomically, certain groups appear more vulnerable to change than others: thus amphibians, and freshwater organismsin general, exhibit higher levels of threat and steeper rates of population decline than do better-known groups such as birds or mammals. Within groups, phylogenetically distinct, ancient, and species-poor lineages seem consistently to be faring disproportionately badly. Some generalist species are expanding their ranges, either naturally or as invasive aliens, whereas many ecological specialists are in decline.
• Spatially, most species losses to date have been concentrated on islands.Disproportionately high rates of contemporary habitat conversion in endemic-rich areas of the tropics, where areas of dense human settlement and high species richness tend to coincide, mean that impending extinctions are particularly concentrated in tropical island and montanesystems. In temperate regions, in contrast, substantial historical reductions in habitat extent have led to relatively few global extinctions (due in part to species having larger ranges at higher latitudes). Currently, populations and habitats are expanding in some temperate regions, such as temperate forests.
• Temporally, two patterns stand out. The first is that the scale of loss is in general increasing(although it is important to note that, both on land and at sea, preindustrial human-caused losses were also very substantial. The second pattern is that the anthropogenic drivers of loss are also changing; for example, invasive species and overexploitation were the predominant causes of bird extinctions in historic times, while habitat conversion, especially to agriculture, is the most significant driver currently facing threatened species, with climate change predicted to emerge as another major threat in the near future.
• Third, changes are complex. E.G., It is
also becoming clear that often ecosystems
respond not linearly to external changes
but in a stepwise manner (Myers 1995).
Thus cumulative biotic or abiotic
pressures that at first appear to have little
effect may lead to quite sudden and
unpredictable changes once thresholds
are crossed.
MA Synthesis Chap. 28
•Skip It.•Taken off syllabus
last week.
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Theme 3: Interacting with
Environment as Resource & HazardNatural Resources
We’ll begin Theme 3 with look at natural resources management
principles (see the reading for some basic intro)
• Resources: material goods/services we derive
from the environment.
• Technology, economics, and culture definenatural resources: soil, uranium, even “naturalness” defined at different times by different societies.
