Ch26- Large Scale Patterns

biological diversity

the number of living organisms inhabiting the Earth

Most diverse group of organisms?

Insects, they have over 1 million species

Long-term evolutionary changes in global diversity have largely been the result of…

Speciation and extinction

Mass extinctions: End of the Permian (225 mya)

90% of marine invertebrates lost mostly likely due to volcanic activity

Mass extinctions: End of the Cretaceous (65 mya)

Dinosaurs and many other species went extinct likely due to asteroid

Mass Extinctions: During the Pleistocene (10,000 years ago)

Ice-age mammals went extinct, caused by movement of ice sheets and/or hunting by humans

Mass Extinctions: Modern extinctions (since 1600)

75% of extinctions have been the result of human activity

Global and regional patterns of species richness arise from shared ecological and evolutionary drivers:

1. Energy availability

2. Climate

3. Habitat heterogeneity

4. Evolutionary history

5. Area & isolation

Patterns of Species Diversity: Latitudinal Diversity Gradient

biodiversity increases from the poles toward the tropics.

• High latitudes have fewer species than low latitudes

• Arctic tundra has fewer species than tropical rainforests

• This pattern is seen in both aquatic and terrestrial environments

Vascular plants tend to show peak diversity in…

the region around the equator

Species richness for cactuses is ____ in the equatorial region

low; they have adapted to desert regions

Over 25 different mechanisms have been proposed to explain the relationship between latitude and diversity, including:

• age of the community

• climate stability over time

• spatial heterogeneity of the environment

• ecosystem productivity

Tree movement during the ice ages can show the effects of climate stability. What does it look like in North America and tropical regions?

• North America: glaciers pushed trees south and then north again as they melted

• Tropical regions: didn’t have this back-and forth movement, so their plant communities stayed more stable

PET (potential evapotranspiration)

High PET means lots of energy, and more energy supports more life

• higher biomass

• bigger populations

• more species

productivity

more plant growth, more resources, more environmental energy, more species

Ocean net primary production [NPP] increases or decreases from the equator toward the poles?

increases, seasonality shapes marine biodiversity, especially in the Northern Hemisphere during the summer

In higher latitudes, surface
waters are ____ ______
in spring and summer and
____ in winter
very low in winter

highly productive; very low

Vertebrate species richness relates more strongly to ________ than to plant productivity

temperature and thermal energy; temp affects animals directly whether they are endo (spend less energy on heating their bodies when it is warm) or ectotherms (rely on an external heat source)

As elevation increases, biodiversity ____

decreases; temperature and productivity decreases so there are less species

Patterns of Species Diversity: Island Biogeography Theory

Species richness on an island reflects a balance between immigration and extinction; large islands support more species, and small islands have fewer, which are also more vulnerable to stochastic events

Distance of islands from the mainland also matter:

near islands have higher immigration rates and more species richness

Island Biogeography Theory can be applied to any isolated habitat, not just islands, such as: (name 3)

1. alpine zones (mountain tops)

2. ponds

3. isolated forests

Regional Patterns of Diversity: Alpha diversity

the local species diversity of individual communities; ex: one acre in florida

Regional Patterns of Diversity: Beta Diversity

variation in species composition among communities in a geographic area (ex: species in a swamp vs a nearby scrub habitat)

Regional Patterns of Diversity: Gamma diversity

total species diversity across all communities in a region (ex: the entire Everglades region)

hotspots

regions of unusually high diversity both in species richness and endemism (endemic species). There are 35 hotspots, 2.3% of Earth’s land area contains 50% of global endemic plant species, 29% of global endemic freshwater fish species, and 77% of all terrestrial vertebrate species