Organization of Life & Symbiosis

How is Life Organized? Species- all organisms of the same kind that breed together Ex: squirrels Populations- all members of a species living in the same area, interbreeding together Ex: all squirrels at MHS Communities- interactions between different populations Ex: all squirrels, trees, pigeons, students, grass, etc interacting @ MHS Ecosystems- interactions between all populations and their surrounding environments Ex: how animals & plants interact with soil, air, water Distinctions between ecosystems is not always clear EX: forest on edge of field may share similar organisms.

So many organisms, how can they all coexist? Everything has a habitat- place where it lives. Everything has a niche- or role in its habitat. How it gets food, interacts with other populations, or service it provides to community. Generalists- wide range of food & habitats (raccoons, cockroaches) Specialists- specific food sources & habitats (pandas); less resilient to changes in environment

What is the Law of Competitive Exclusion? No two species will occupy the same niche and compete for exactly the same resources in the same habitat for very long. Eventually, one species will outcompete the other and push the weaker species out of the habitat, or cause its extinction. Could result in two insectivores feeding in same tree, just at different times of the day.

More on competition… Compete for food, chemical nutrients in soil, space, mates, etc. Intraspecific- competition within a species Trees provide shade so their own seedlings can’t grow underneath them so no competition for sun Caterpillars eat leaves while adult butterflies eat nectar. Reduces competition for food sources Some create a territory to prevent competition Interspecific- competition between two different species Ex: when different weeds produce numerous seeds & race to cover most ground secrete substance that inhibits root growth different herbivores on savanna compete for grasses

Besides competition, how else do species interact? PREDATOR-PREY Predator- an organism that feeds directly upon another living organism, may or may not kill prey Includes herbivores, carnivores, omnivores Help force evolution of prey species Leads to coevolution- exert selective pressure on each other- evolve in response to each other

How else do species interact? PARASITE-HOST Parasites feed directly on another living thing but do not kill it in the process. Ex: ticks suck blood from dog

How else do species interact? COMMENSALISM one member benefits, the other is not substantially benefited or harmed. Ex: cattle egrets feed on insects stirred up by grazing cattle Clownfish gets protection from sea anemone which is not helped or harmed by fish. Bromeliads grow on tree branches to reach sunlight

How else do species interact? MUTUALISM Both members benefit significantly from the relationship Ex: Lichens- combo of fungus (provides water & place for algae to grow) and algae (provides food for both) Insects & their pollinators Ants and acacia trees

How else do species interact? KEYSTONE SPECIES A species or group of species whose impact on a community are much larger than would be expected from mere abundance. Ex: sea otters & kelp beds; tropical figs & frugivores (fruit eaters) http://www.grinningplanet.com/2004/06-22/keystone-species-article.htm Keystone species increase niche diversity because without them other species cannot survive- may either move to new habitat or become locally extirpated

How do organisms defend themselves against predation & parasitism? Chemical defense- smell bad or taste bad Batesian mimicry Harmless species mimics harmful Ex: monarch butterfly & viceroy butterfly; moth has eyespots, looks like owl Mullerian mimicry Two species that are harmful develop same patterns/colors Most wasps have yellow/black banding patterns Camouflage- look like dead leaves or twigs or even bird poop