Exam 1 key posted Office Hours Bonus

Fig 52.7 Carrying Capacity exponential growth stationary phase

What happens as populations approach their carrying capacity?

UN Department of Economic and Social Affairs Population Division (2004) Fig 52.17

Fig 52.8

CB 55.2 Genetic Diversity Biodiversity- number of species within an area Ecosystem Diversity

Increased numbers of one species can reduce the population of other species

Fig 54.2 Ecosystems on Earth: resources are not evenly distributed

Larger areas can support more biodiversity Islands Fig 53.24b

Larger areas can support more biodiversity # bird species

Water is critical for biodiversity

Fig 50.28

rain quantity and rain pattern affect productivity and species diversity

Removing resources reduces biodiversity Australian tree hole communities (leaf litter supports bugs etc) 1/10th1/100th

New predators can have an affect throughout the ecosystem

Interactions include area, climate, competition, density...

Have we overstated the tropical biodiversity crisis? William F. Laurance Trends in Ecology & Evolution Vol. 22: February 2007

Are we on the verge of a massive die-off of tropical species?

Changes in Extinctions and Diversity

Are we on the verge of a massive die-off of tropical species?

Increased rural density leads to decreased forest.

This is because rural slash-and- burn farmers cause most forest loss.

The good news? About 21–24% of species in the Asian tropics and 16–35% of species in the African tropics are threatened with possible extinction.

Rural populations are expected to decline.

Substantial areas of agricultural land are likely to be abandoned, because the population growth rates of many developing nations are slowing and because of increasing urbanization. This could enable significant forest regeneration, which could help buffer species losses from deforestation.

Human vs Natural Disturbances

Extinction rates are likely to be higher in biodiversity hotspots

Fig 55.4 Terrestrial Biodiversity Hotspots

the 16 hotspots that sustain tropical forest have already lost, on average, 90% of their forest cover

CB Rainforest clear cutting

Not all habitats are equal

A third to a half of all old-growth species avoid younger (<30-year-old) regrowth.

In many tropical regions, future pressures on forests will be determined more strongly by industrial drivers, globalization and macroeconomic forces than by local population density.

Rural populations are expected to decline, but increased urban population will demand more resources.

The precautionary principle maintains that one should err on the side of caution in conservation matters.

We need to evaluate critically the degree to which regenerating and degraded habitats, which are increasing dramatically at the expense of old-growth forests, can sustain tropical biodiversity

Why are species going extinct? Fig 55.6