LIFESCI 7B Lecture Notes - Lecture 7: Hispaniola, Niche Differentiation, Primary Production
10 Jun 2018
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48.4 Global Biodiversity
● Tropical rain forests harbor the highest number of plant species, in general the amount of plant diversity
tails off toward the poles.
● Deserts have particula!rly low plant diversity, a pattern linked to their low primary productivity.
● Mediterranean climates—temperate regions with dry summers and wet winters—can support large
numbers of plant species, for example along the southern tip of Africa, southwestern Australia, and
Mediterranean Europe.
○ These regions show that additional factors only indirectly linked to climate influence regional
plant diversity, including habitat diversity (in Mediterranean regions, a mixture of woodland,
savannahs, and grassland) and frequent fires
● This pattern can be seen in animals as well, with the greatest diversity in tropical regions, and the least
toward the poles
Why does biodiversity decrease from the equator toward the poles?
● latitudinal diversity gradient The increase in species diversity from the poles to the equator.
○ Higher productivity at equator than at the poles
■ productivity refers to the rate of generation of biomass in an ecosystem
● One hypothesis, (widely supported) looks to the relative ages of tropical and higher-latitude biomes.
○ Tropical biomes tend to be older, having evolved over tens of millions of years, whereas biomes
at higher latitudes have been shaped by climatic change, and ultimately an ice age, within the
past few million years.
● Another hypothesis is that temperate communities have fewer species because it is relatively difficult to
adapt successfully to cold, dry winters and the range of weather typically experienced at higher
latitudes.
○ Species of high altitudes have adapted to broader range of conditions than that at the equator,
have larger geographic ranges than tropical ones (which are adapted to the narrow range of
environmental variation experienced in any particular place)
● Another hypothesis: many insects and fungi specialized to attack particular kinds of tree are generally
more abundant in wet tropical forests, and so trees of a given species tend to be as far apart as they
can be, thus reducing the chance of being found by their enemies.
● where there are more species of trees, there are also more species of animals and other consumers!!!
○ High diversity → low population density in tropical regions
● Both on land and in the sea, biodiversity hotspots occur predominantly in tropical to subtropical
environments.
○ reflects the higher species diversity typical of lower latitudes, but it also highlights that tropical
communities contain a relatively high proportion of endemic species, species found in one
place and nowhere else.
○ Continued speciation+ limited ability to successfully colonize new areas affects distribution of
hotspots
■ burden of conservation efforts falls disproportionately on developing countries.
Evolutionary and ecological history underpins diversity.
● Amber fossils from the hymenea trees of HIspanola preserve record of forest diversity and ecology 30-
23 million years ago
● Reveals species associated w/ the hymenea trees (majority of which indistinguishable from modern
species today!) as well as species no longer found on Hispanola
○ resource partitioning began long ago in the Hispaniola rain forest
● Such fossils allow us to add a deeper dimension of time to our understanding of how ecosystems have
come to be.
History of Biodiversity
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● Major groups of organisms that charaterize biodiversity: vertabrates, mollusks, insects, fungi, flowering
plants, etc.
● Biodiversity of microscopic organisms as well
● How and when did biodiversity evolve?
○ Precambrian: 4600-542 million years ago; formation of
earth, evolution of life (bacteria, archaea, eukarya),
multicellular life, animals algae, ediacaran fauna
■ 3.7 billion years ago: carbon ratio in zircons
suggest life (when life first evolved)
● Bacteria: 3.45 bya
● Eukaria: 1.8 bya
● Archaea: 3.5 bya
■ Oldest stromatolite (bacteria) fossils date back
3.45 bya
■ 2.1 bya: oldest fossils of multicellular life date back
to this time
● Enigmatic fossils from 2.1 bya
● Earliest fossils of eukaryotes (algae) 1.6 bya
■ LONG interval between orgin of life and appearance of mutlicellular organisms
● For 2.1-1.6 billion years, story of archaea and bacteria; (eukyotes minor players
at the time)
■ Very first animals: early animal life resemble sponges (earliest fossils 650 mya);
biomarkers also demonstrate existence of sponges during this time
■ Ediacarn period: 635-541 mya; diverse and unique animals dominated oceans from 575-
535 mya; dawn of animal diversity and taxa hard to place taxonomically (poorly
understood);
● Largely softbodied and have very few characteristics
● End of period=radiation of multicellular eukaryotes
○ Paleozoic: 542-251 MY: rise of animals, terrestrial plants, vascular plants, mosses, tree ferns,
insects/spiders, jawless and jawed fish, teleosts, sharks, tetrapods (amphibians, amniotes,
reptiles nad mammal lineages), mass extinctions in Ordovician, Devonian, Permian
■ Cambrian: starts Paleozoic era
● Cambrian explosion: explosion of diversification; rapid appearance of diverse life
forms in fossil record (disproportionate concentration of diversification during
period of time--cambrian; over 10x rate of evolution!)
○ Periods of rapid diversification: evolutionary radiations
● Most major groups of animals livign today appeared during cambrian
● O2 concentration was near modern explosion
● Most life aquatic
■ Ediacaran vs. Cambrian
● Only a fraction of ediacaran fauna share traits w/ existing lineages
○ Almost extinct within 40 million years
● Most existing lineages found in fossil record during cambrian period
○ Includes our own lineage, the chordates
■ Ordovician and Silurian periods (488-419 mya)
● Radiation of marine organisms; brachiopods, cephalopods, echinoderms;
terrestrial plants
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Tropical rain forests harbor the highest number of plant species, in general the amount of plant diversity tails off toward the poles. Deserts have particula!rly low plant diversity, a pattern linked to their low primary productivity. Mediterranean climates temperate regions with dry summers and wet winters can support large numbers of plant species, for example along the southern tip of africa, southwestern australia, and. These regions show that additional factors only indirectly linked to climate influence regional plant diversity, including habitat diversity (in mediterranean regions, a mixture of woodland, savannahs, and grassland) and frequent fires. This pattern can be seen in animals as well, with the greatest diversity in tropical regions, and the least toward the poles. Why does biodiversity decrease from the equator toward the poles? latitudinal diversity gradient the increase in species diversity from the poles to the equator. Higher productivity at equator than at the poles.
