Biological Communities Chapter 17

How Organisms Interact in Communities Evolution in Communities lead to special relationships among some species Examples include: Predator/Prey Parasitism Symbiosis

Predators and Prey Predators Prey Population sizes are linked Consumers that hunt other organisms Prey Organisms upon which a predator feeds Population sizes are linked Increase in prey  Increase in predator Decrease in prey  Decrease in predator Population of prey regulates population of predator Ex. Lynx and Hare populations

Parasitism One organism feeds on the tissues or body fluids of another (host) Host – organism on which a parasite feeds Parasites live on or in organism Most do not kill their hosts Parasite populations depend on the host size and populations Ex. Tapeworms in mammal intestines

Symbiosis Relationship where two species live together closely Parasitism is an example Commensalism One species benefits, the other is neither helped nor harmed Ex. Barnacles and whales Mutualism Both species benefit Ex. Insects and flowers

How Competition Shapes Communities Competition occurs when two species use the same resource. Examples include: food, nesting sites, living space, light, water, etc Niche refers to a species role in an ecosystem…where it lives, the “job” or role it plays… If several species occupy the same niche in an ecosystem competition exists

Population Growth Populations grow quickly Exponential Growth Population growth in which the rate of growth in each generation is a multiple of the previous generation Ex. 2  4  8  16  32  64  Is there a limit?

Carrying Capacity If population grows, resources become scarce Individuals compete, death rate rises Birth rate decreases, if resources are low When death rate equals birth rate, population stops growing Carrying Capacity The number of individuals that can be supported by an ecosystem Represented by an S-Shaped Curve (graph)

Limiting Factors Forces that slow population growth Density-Dependent Depends on population size S-Shaped curve Ex. Food, predation, disease Density-Independent Affects same percentage of population regardless of size Ex. Habitat damage, such as hurricanes and fires Boom and Bust curve – grows exponentially then collapses

Major Biological Communities Elements of climate (temperature, and moisture) determine ecosystems. Sometime also called limiting factors Major biological communities that occur over a large area are called biomes. Vary depending on latitude or longitude (land biomes) or water type and depth

Terrestrial Biomes Tropical Rain Forests Savannas Taiga Tndra Deserts Temperate Grasslands Temperate Deciduous Forests Temperate Evergreen Forests

Aquatic Communities Freshwater Estuaries Marine Ponds, Lakes, Rivers Wetlands Estuaries Marine Shallow Ocean Surface of Open Sea Ocean Depths