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Lecture 3

Lecture 3 study guide (2010 fall semester)

Environmental Science
Course Code
Cynthia Bongard

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Lecture 3: Contemporary Cues for Limits & Driving Forces
Latitudinal Diversity Gradient:
low latitude or closer to equator, the more species diversity (seen in birds)
30% of worlds 9040 bird species occur in Amazon, and another 16% in Indonesia
Rainforest is 6% of world land mass, but have more than half of worlds species
Similar pattern for shallow marine fauna: plankton, benthos (bottom dwellers),
and especially coral reefs (greatest diversity)
Exceptions: in temperate zones, there are a few plants and animals that are more
diverse: conifers, aphids, salamanders
Possible factors generally contributing to biodiversity:
Climate (precipitation, humidity and etc.)
Solar energy
Amount of habitable terrain
Variety of habitats available
Amount of frequency of environmental disturbance
Degree of isolation of the faunas and floras (all of animal and plant life of any
particular region or time)
Idiosyncrasies of history:
Energy-Stability-Area Theory of Biodiversity (ESA Theory):
1.The more solar energy, the greater diversity
However, energy and biomass alone do not explain tropical dominance of biological
Why dont we have one super species in each habitat? Very few habitats do have dominant
species, a lot dont, however.
Rapoports Rule:

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As you approach equator (or descend a mountain go down in altitude), the
ranges of individual species shrink steadily (alternatively, taxa have larger
ranges in polar regions)
Winter adaptations: due to role of seasons in temperate regions, organisms have
to adapt to swings in climate, and occupy larger geographical ranges/distributed
across a wider range of latitudes
Stable climates (in tropics) with muted seasons allow more kinds of organisms to
specialize in narrow pieces of environment, they outcompete generalist species
that are co-occuring; this cause more biodiversity in tropics than in temperate
adaptations to a greater breadth of local environments, forcing species into
different dietary needs promotes biodiversity
there are exceptions however: red mangrove swamp in tropics coastal regions
have >90% of plant species, but this is rare
2.The more stable the climate, both from season to season and from year to year, the
greater the diversity, because organisms can specialize in small environmental
Persistence and evolution of larger species due to stable climates as well
Piggybacking (small on large): epiphytes (orchids, ferns, cacti and etc. make 10%
of higher plants, 28,000 species in 84 families) take advantage of trees as
support; in turn, epiphytes are home to a range of aquatic/terrestrial animals
(mites, nematodes, insects, amphibians and etc.)
3.The larger the area, the greater the diversity: tenfold increase in area, doubling in
number of species
Other key factors:
Evolutionary time, stability: for piggybacking and symbioses to develop;
glaciations does not reach equator, so it has more stability and evolutionary time,
and therefore has higher biodiversity
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