Chapter 4

1. Chapter 4 Evolution, Biological communities, and Species interactions

2. Limitations of species on where they live • Physiological stress due to inappropriate levels of some critical environmental factor, such as moisture, light, temperature, pH, or specific nutrients • Competition with other species • Predation, including parasitism and disease • Luck

3. Critical factor and tolerance limits The critical factor for saguaro cacti is the temperature, they don’t do well if the temperature is below freezing for more than 12 hours. Tolerance limits of species are helpful indicators of specific environmental characteristics. How?

4. Tolerance limits

5. Ecological niche • Generalist- ecological niche is broad- brown rat • Specialists- have more exacting habitat requirements - giant pandas • Much of the flora and fauna on the Galapagos were endemic and highly specialized to exist in their unique habitat

6. Competitive exclusion principle and resource partioning • Ex. Swallows and insectivorous bats both catch insects, but some insect species are active during the day and others at night.

7. speciation • Allopatric speciation caused by geographic isolation and behavioral isolation • Sympatric speciation – doubling or quadrupling the chromosome number of their ancestors (plants)

8. Types of selection • Directional selection- shifts towards one extreme of the trait • Stabilizing selection- narrows the range of a trait • Disruptive selection- cause traits to diverge to the extremes

9. Evolution is still at work • Geneticists modifying fruit fly properties- only flies with the most bristles could mate- after 86 generations the number of bristles had quadrupled • Large billed finches introduced to Galapagos -which originally only had medium billed finches- large billed better at eating large seeds- medium billed depended more on the smaller seeds- severe drought in 2003-2004 – most of the large billed finches disappeared….why?

10. Evolution is still at work • Widespread application of pesticides- rapid evolution of resistance in more than 500 insect species • 90,000 Americans die every year from hospital-acquired infections, most which are resistant to one or more antibiotics- microbes are evolving to become impervious to them • Why do we have to have a new flu vaccination each year?

11. Taxonomy • Six Kingdoms: animals, plants, fungi (molds and mushrooms), protists,(algae, protozoans, slime molds), bacteria (eubacteria) and archaebacteria (ancient single celled organisms that live in harsh environments)

12. Competition leads to resource allocation • Intraspecific competition can be reduced by • 1) the young of the year disperse • 2) exhibit strong territoriality • 3) resource partitioning between generations • Interspecific competition is modeled by the competitive exclusion principle

13. Predation • It affects: • 1) all stages of the life cycles of predator and prey species • 2) many specialized food-obtaining mechanisms • 3)the evolutionary adjustments in behavior and body characteristics that help prey escape being eaten, and predators more efficiently catch their prey

14. Adaptations to help avoid predation • Coevolution- plants and pollinators • Batesian mimicry- harmless species resemble poisonous or distasteful ones • Mullerian mimicry- involves two unpalatable or dangerous species who look alike • Camoflauge

15. symbiosis • Mutualism- a parasite-eating red-billed oxpecker and a parasite-infested impala • Commensalism- mosses growing on trees in the moist tropics • Parasitism- tapeworm in humans

16. Keystone species • Plays a critical role in a biological community that is out of proportion to its abundance • Seem to be more common in aquatic habitats than in terrestrial ones

17. Productivity Primary Productivity- Photosynthetic rates are regulated by light levels, temperature, moisture, and nutrient availability Even in the most photosynthetically active ecosystems, only a small percentage of the available sunlight is captured and used to make energy-rich compounds.

18. Abundance and Diversity • As a general rule, diversity decreases but abundance within a species increases as we go from the equator toward the poles. • Productivity is related to abundance and diversity, both of which are dependent on the total resource availability in an ecosystem as well as the reliability of resources, the adaptations of the member species, and the interactions between species

19. Community structure • Ecological structure refers to patterns of spatial distribution of individuals and populations within a community, as well as the relation of a particular community to its surroundings. • Random-individuals live wherever resources are available • Uniform- often the result of biological competition • Cluster- protection, mutual assistance, reproduction, or access to a particular environmental resource • Distribution in a community can be vertical as well as horizontal. ( tropical forest, aquatic)

20. Resilience • Constancy- lack of fluctuations in composition or functions • Inertia- resistance to perturbations • Renewal- ability to repair damage after disturbance • Two theories- • 1.the more complex and interconnected a community is, the more stable and resilient it will be in the face of disturbance • 2. In a diverse and highly specialized ecosystem, removal of a few keystone members can eliminate many other associated species

21. Edge effects and ecotones • A community that is sharply divided from its neighbors is call a closed community. • Communities with gradual or indistinct boundaries over which many species cross are called open communities

22. Ecological succession During succession, organisms occupy a site and change the environmental conditions. Primary succession- land that is bare of soil- is colonized by living organisms where none lived before When an existing community is disturbed, a new one develops from the biological legacy of the old in a process called secondary succession. You can see secondary succession all around you, in abandoned farm fields, in clear-cut forests, and in disturbed suburbs and lots.

23. Disturbance • Disturbances are plentiful on earth: landslides, mudslides, hailstorms, earthquakes, hurricanes, tornadoes, tidal waves, wildfires, and volcanoes just to name the obvious. • Ecologists generally find that disturbances benefits most species, much as predation does, because it sets back supreme competitors and allows less-competitive species to persist. • From another view, disturbance resets the successional clock that always operates in every community.