Environmental ScienceOctober 22, 2008 Mrs. RosenMrs. Waldinger Do Now: Describe physical barriers that would define an ecosytem/biome. Aim: How do limiting factors affect species in biological communities? HW #8: Packet is due Monday, 10/27/08.

Speciation  Given enough geographical isolation or selective pressure, members of a population become so different from their ancestors that they may be considered an entirely new species.  Alternatively, isolation of population subsets, preventing genetic exchange, can result in branching off of new species that coexist with the parental line.

Ecological Niche  Habitat - Place or set of environmental conditions where a particular organism lives.  Ecological Niche  Role a species plays in a biological community (e.g. large grassland herbivore)  Total set of environmental factors that determines a species’ distribution.  Generalists - Broad niche  Specialists - Narrow niche  When generalists and specialists collide, generalists usually win.

Competition

Law of Competitive Exclusion  No two species will occupy the same niche and compete for exactly the same resources for an extended period of time.  One will either migrate, become extinct, or partition the resource and utilize a sub-set of the same resource.  Given resource can only be partitioned a finite number of times.

Resource Partitioning

Predation  Feeds directly upon another living organism, whether or not it kills the prey in doing so.  Mosquitoes prey on humans  Prey most successfully on slowest, weakest, least fit members of target population.  Reduce competition, population overgrowth, and stimulate natural selection.  Co-evolution (arms race)

Co-Evolution and Disease  If a disease kills too quickly, it can’t spread  Disease can moderate while host becomes more resistant (measles)  Disease can be lethal but messy (cholera, ebola)  Disease can be lethal but slow-acting (AIDS)

Keystone Species  Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance.  Large predators  Critical food organisms (bamboo and pandas)  Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.

Competition  Interspecific - Competition between members of different species.  Intraspecific - Competition among members of the same species.  Often intense due to same space and nutritional requirements.  Territoriality - Organisms defend specific area containing resources, primarily against members of own species.  Resource Allocation and Spacing

Mutualism Intimate living together of members of two or more species.  Commensalism - One member benefits while other is neither benefited nor harmed.  Cattle and Cattle Egrets  Symbiosis - Both members benefit.  Lichens (Fungus and cyanobacterium)  Parasitism - One member benefits at the expense of other.  Humans and Tapeworms

Commensalism: Epiphytes:

Symbiosis - Lichens

Defensive Mechanisms  Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable, dangerous or poisonous species  Viceroy and Monarch butterfly  Mullerian Mimicry - Two unpalatable species evolve to look alike  Bees and Wasps  Camouflage  Advertising and warning (coral snake)  Attracting prey, pollinators, mates, etc.

Abundance and Diversity  Abundance -Total number of organisms in a community.  Diversity - Number of different species, ecological niches, or genetic variation.  Abundance of a particular species often inversely related to community diversity.  As general rule, diversity decreases and abundance within species increases when moving from the equator to the poles.

Trophic Level (Food Chain)  A pond  Phytoplankton  Zooplankton  Small Fish  Larger Fish  Higher predators (birds, mammals)  Organisms are at same trophic level if they get their food from similar sources

Trophic Level (Food Chain)  A forest  Decaying organic matter  Insects  Small mammals and birds  Higher predators (owls, foxes, bears)  A Pasture or Grassland  Grass  Herbivore  Higher predators

Trophic Level (Food Chain)  At each level, some matter goes into biomass  Most goes into energy and metabolism  Hence each level needs about 10x as much energy, has fewer individuals  Bio-Accumulated chemicals get more abundant higher up the food chain

Food Requirements  Warm-blooded organisms require more food than cold-blooded  Predator/prey ratio higher for cold-blooded  Indication that some dinosaurs may have been warm-blooded  Large organisms eat less in proportion to their mass than small ones  Shrew: 100%+ per day  Human: 1% per day

Improbable Movie Biology  Things that eat people (Morlocks, The Time Machine)  Really huge carnivores (The Phantom Menace)  Huge carnivores in empty environments (Empire Strikes Back, Return of the Jedi)  Ultra-voracious carnivores (Jaws, Alien, Anaconda, Jurassic Park)

Edges and Boundaries  Edge Effects - Important aspect of community structure is the boundary between one habitat and others.  Ecotones - Boundaries between adjacent communities.  Sharp boundaries - Closed communities  Indistinct boundaries - Open communities

COMMUNITIES IN TRANSITION  Ecological Succession  Primary Succession - A community begins to develop on a site previously unoccupied by living organisms.  Pioneer Species  Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site.

Terrestrial Primary Succession

Ecological Succession  Ecological Development - Process of environmental modification (facilitation) by organisms.  Climax Community - Community that develops and seemingly resists further change.  Equilibrium Communities (Disclimax Communities) - Never reach stable climax because they are adapted to periodic disruption.

Introduced Species  If introduced species prey upon or compete more successfully than native populations, the nature of the community may be altered.  Human history littered with examples of introducing exotic species to solve problems caused by previous introductions.  Mongoose and Rats in Caribbean

Summary:  Critical Environmental Factors  Adaptation  Natural Selection  Speciation  Ecological Niche  Population Dynamics  Community Properties  Succession  Introduced Species