Lecture Outline - Chapter 32

32.1. Competition (p. 642)

1. Occurs when organisms compete for same food, living space, or mates.
2. Can be avoided if species do not share the same resource.
3. Competitive Exclusion Principle
   • a. No two species can occupy the same niche at the same time.
   • b. A niche consists of the full range of energy, nutrient, and survival requirements of an organism.
   • c. For example: two species of paramecia survive in same test tube; one feeds on bacteria on bottom, one feeds on bacteria in suspension.
   • d. Six species of monkeys live in close proximity but have different habitats and food requirements. (Fig. 32.1)
   • e. When two species of bacteria feed on same bacterial food, only one species survives. (Fig. 32.2)
   • f. Two species of barnacles live in intertidal zone; distribute free-swimming larvae over all exposed rocks.
     • i. Balanus is faster growing; crowds out Chthamalus in lower tidal zone; cannot survive in higher drier zone because it is susceptible to drying out.
     • ii. Chthamalus endures drier conditions in upper tidal zone. (Fig. 32.3)
   • g. Exotic species (introduced to new regions) thrive in absence of normal competitors.
     • i. Carp imported into United States are more prevalent than native species.
     • ii. Ornamental tree Melaleuca introduced to Florida is pest in Everglades.
     • iii. Burro from Ethiopia and Somalia is threat to survival of deer, pronghorn antelope and desert bighorn sheep in Grand Canyon.
   • h. Current concern that genetically-engineered organisms might outcompete native species.

1. When predator feeds on prey.
2. Predator adaptations include: talons/claws and sharp beaks/teeth, keen eyesight, etc.
3. Predation Affects Prey Population Size
   • a. Predators and prey are co-dependent.
     • i. When Didinia and Paramecia are in same test tube, Didinia engulf all the Paramecia and then die of starvation; if some of Paramecia have a refuge to hide, the populations survive.
     • ii. Records of fur pelts show lynx populations fluctuate with snowshoe hare populations. (Fig. 32.4)
     • iii. Elimination of predators causes problems with overpopulations of prey:
       -killing off coyotes released prairie dog populations.
       -killing of dingoes that attacked Australian sheep released rabbit and wallaby populations.
       -protection of burrows has increased their populations and threatens native animals.
4. Community Diversity and Predation
   • a. Keystone predators determine structure of whole community.
     • i. Sea star Pisaster keeps mussel Mytilus from outcompeting with other mussels; removal of Pisaster causes explosion in Mytilus populations.
     • ii. Sea otters feed on invertebrates and increase brown kelp population.
5. Prey Defend Themselves
   • a. Both plants and animal prey evolve strategies to decrease predation.
   • b. Antipredator defenses include concealment, fright, warning coloration, and vigilance. (Fig. 32.5)
6. Mimicry Can Help
   • a. One species resembles another for its own benefit.
   • b. Mimicry helps organism to both avoid capture and to capture food.
   • c. Organisms can use mimicry of environment, or camouflage, to avoid predators.
   • d. Batesian Mimicry
     • i. Named for Henry Bates who first described it.
     • ii. Mimic matches a model that has a successful antipredator defense.
     • iii. A harmless syrphid fly resembles coloration of wasp; predators stung by wasps avoid this fly.
   • e. Mullerian Mimicry
     • i. Named for Fritz Muller who first described it.
     • ii. Many black-and-yellow insects (bees, wasps, hornets) share defense and warning coloration.

1. Symbiosis is a close association between two species where at least one species is dependent upon the other. (Table 32.1)
2. Coevolution has occurred for them to become closely adapted; the evolutionary fate of one may be dependent upon fate of the other.
3. Parasitism is Destructive
   • a. Parasite (usually smaller) derives nourishment from the host (usually larger).
   • b. Parasites include: all viruses and some bacteria, protists, plants, and animals.
   • c. Endoparasites are usually small and live inside bodies of hosts.
   • d. Ectoparasites are usually larger and live on surface of host.
   • e. Many parasites use secondary host to disperse or complete stages of development. (Fig. 32.7)
   • f. Dutch elm disease is example of damage by parasitic fungus.
4. Commensalism is Not Harmful
   • a. Relationship between two species where one is benefited and other is neither harmed or benefited.
   • b. Host may provide a home or transportation for benefited species.
     • i. Barnacles attach to backs of whales or shells of horseshoe crabs.
     • ii. Remoras attach to sharks by suction cups; feed on shark's "leftovers."
     • iii. Epiphytes are plants that grow among tree branches; obtain air, light and water without damaging tree.
     • iv. Clownfish live amid tentacles of sea anemone, receives protection.
5. Mutualism is Beneficial to Both
   • a. Relationship where both members benefit.
   • b. Ant-Acacia Tree Mutualism
     • i. Bullhorn acacia tree lives in South America.
     • ii. Provides home for the ant Pseudomyrmex ferruginea. (Fig. 32.8)
     • iii. Swollen acacia thorns are hollow, provide home for ant larvae.
     • iv. Ants feed from nectaries at base of leaves.
     • v. Acacia provides ants with fat and protein laden nodules called Beltian bodies at leaf tips.
     • vi. In return, ants protect plant from herbivores that might eat acacia; also clear away seedlings around acacia and prevent it from being "shaded out."
   • c. "Good" Bacterial and Fungal Relationships
     • i. Normal intestinal bacteria help provide us with vitamins we cannot get synthesize for ourselves.
     • ii. Bacteria in protozoa in termite gut allow digestion of cellulose.
     • iii. Mycorrhizae (fungus-root associations) improve the uptake of nutrients in plant, protect plant roots against other pathogens and produce plant growth hormones; in return, fungus gets carbohydrates from the plant.
   • d. Insect pollinators and flowers are classic examples of coevolved organisms dependent upon one another.

1. Communities are composed of species adapted to the conditions of the community.
2. Communities differ in diversity, the numbers and variety of organisms present.
3. Number of species increases towards the tropics, decreases towards the poles.
   • a. Partly due to longer growing season and greater biomass that can be produced.
   • b. Also due to more species.
4. Competitors evolve to fill different niches. (Fig. 32.1)
5. Predators keep populations in check, reducing competition allowing more species to coexist.
6. Stratification provides the architecture for organisms to live at many levels.
7. Theory of Island Biogeography
   • a. Island population is a balance between immigration and extinction.
   • b. Smaller populations more likely to become extinct following disturbance.
   • c. Mainland communities become "islands" amidst farms, towns, cities, etc.
   • d. The smaller the "island," the higher the risk of extinction; human activity is making many natural communities smaller.
8. Succession
   • a. Succession is a sequential change in species within a community.
   • b. Primary Succession
     • i. Begins with bare rock; takes very long time.
     • ii. Weathering of wind and rain plus pioneer species such as lichens and mosses begin to build up soil.
     • iii. Herbaceous or grass stage grows on deeper soil and shades out shorter pioneer species.
     • iv. Pine trees or deciduous trees eventually take root; form climax community.
   • c. Secondary Succession
     • i. Begins in abandoned field with soil layers already in place.
     • ii. Moves more rapidly to climax community.
   • d. Early researchers assumed climax communities were determined for each environment; today recognized to be outcome of competition among whatever species are present.
9. Climax Communities Are More Stable
   • a. Early stages of succession show most growth and are most productive.
   • b. Pioneer communities lack diversity, make poor use of inputs and lose heat and nutrients.
   • c. As succession proceeds, species variety increases and nutrients recycle more.
   • d. Climax communities make fuller use of inputs and maintain themselves-they are more stable.
   • e. Humans replace climax communities with simpler communities. (Table 32.2)