Ecology Organization levels of biology.

Ecology (ekos –house ology – study of) Ecology is the study of interactions between organisms and their environment. Ecology entails consideration of biotic factors (other organisms that include prey, predators, parasites, etc.) and …. abiotic factors (such as temperature, light, and water). Ecology is not environmental activism or “tree-hugging.”

Levels of Ecological Investigation

Community Ecology Community ecology examines the question of how populations interact. Questions include: What are the types of species and their numbers within a community (i.e. community structure)? Are there especially critical species for maintenance of the community? What is the relationship (predator, prey, parasite) between species within the community?

Community Structure Types of species: - autotrophs - primary consumers - secondary consumers - tertiary consumers - detritovores - decomposers

Keystone Species Robert Paine – 1969 “a keystone species plays a critical role in maintaining the structure of an ecological community and whose impact on the community is greater than would be expected based on its relative abundance or biomass”

Foundation Species Dayton – 1972 “a single species that defines much of the structure of a community by creating locally stable conditions for other species, and by modulating and stabilizing fundamental ecosystem processes.” Usually a primary producer in both terms of abundance and influence

How Do Species Interact? Species interact in complex ways that are often reduced to three categories: Competition Predation (and parasitism) Mutualism

Interspecific Competition and Gause’s Competitive Exclusion Principle Gause’s Principle: No two species within a community may share the same niche. What’s a niche? A niche is an organism’s way of making a living that includes choices of habitat, food and behavior.

Gause’s Study These two species have the same niche. In competition, one will win out (exclude) the other.

Resource Partitioning Placing another closely related species in with the previous “winner” gives a different result – both species persist. Why? Each species occupies a different part of the environment (i.e. they have different niches) – there’s been a partitioning of resources.

Resource Partitioning Closely related warbler species can occupy the same tree if they partition resources. Competitive exclusion is an important factor in evolution.

Predation, Parasitism and Coevolution Predation (consuming another organism) and parasitism (feeding upon a host organism without causing its immediate death) drive an evolutionary arms race. Predator and prey, host and parasite are locked in a duel to outwit their opponent through adaptations. Predator and prey interactions drive coevolution – coupled adaptive changes in interacting species.

Coevolution of Interacting Species is Widespread Pollinators and the plants they pollinate are often exquisitely adapted for one another.

Camouflage is An Outcome of Predator-Prey Interaction

Mimicry Is An Outcome of Predator-Prey Interactions If a potential prey species develops an effective defense system, other unprotected prey species may come to mimic the protected species. This is Batsian mimicry. One (of many) examples of Batsian mimicry: the stinging yellow jacket and its harmless mimic, the clearwing moth.

Batsian Mimicry Disturbed hawkmoth larva. Snake

If a group of potential prey species develops an effective defense, the different species may coevolve to resemble one other. This is Mullerian mimicry. One example of Mullerian mimicry: the stinging yellow jacket and the stinging cicada- killer wasp – both are noxious. Mimicry Is An Outcome of Predator-Prey Interactions

Mullerian Mimicry Two noxious species of South American butterfly.

Mutualism Mutualism occurs when species interact in a mutually beneficial manner. The oxpecker gets food (ticks and insects disturbed in the grass) and a safe haven from the rhinoceros, and the rhinoceros has parasites (ticks) removed.

Mutualism Mycorrhizal fungi (threads) covering aspen roots: fungi aid in water and nutrient absorption by the aspen and the aspen provides sugars and other food molecules to the fungi.

Ecological succession is the set of changes in community composition that occur over time in a new or disturbed community. Succession at Mt. St. Helens. Ecological Succession Succession after the Yellowstone fires.

Retreating Glaciers at Glacier Bay Alaska Make It a Natural Laboratory for Studying Primary Succession Primary succession occurs when organisms colonize a barren environment.

Primary Succession at Glacier Bay, Alaska A climax community is the stable community at the final stage of succession.

Succession Succession shows some general trends that include: 1) Biomass increase over time. 2) An increase in the number and proportion of longer-lived species. 3) Increased species diversity. Succession on Mt. St. Helens – another site of intense study.