Chapter 54 – Community Ecology

WHAT IS A COMMUNITY??? –A community is a group of populations of various species living close enough for potential interaction

Community Interactions Interspecific – interactions between different species within a community –Competition –Predation –Herbivory –Symbiosis –Disease

Competition Interspecific competition occurs when species compete for a resource that is in limited supply Competitive exclusion principle: one species will use the limiting resources more efficiently thereby eliminating the local competitor. –Example: barnacle species in Scotland

BARNACLE BACKGROUND: –What do you notice about the distribution of the two barnacles? –What abiotic factor(s) may contribute to their distribution patterns?

What happened when Chthamalus was removed from the habitat? –What is the difference between a realized niche and a fundamental niche? BEFORE AFTER

Competitive Exclusion Principle and the Concept of Niche Relates to concept of Niche: the sum total of the biotic and abiotic resources used by a species’ –Fundamental niche = potential –Realized niche = actual

Niche Niche Two species cannot occupy the same niche = leads to competition Resource partitioning: altering ones niche to avoid competition; lizard example Character displacement: characteristics become more divergent; finch beak example Resource Partitioning Character Displacement

Predation Predator kills and eats prey; a +/- interaction Predator mechanisms: acute senses, claws, teeth, fangs, stingers, poison, speed, agility, coloration, and camouflage Defense mechanisms: alarm calls, maternal/paternal protection, mechanical defenses (spikes, spines, and hard shells), chemical defenses (toxins, poisons, and bad taste), coloration (aposematic coloration) and mimicry (Batesian and Mullerian).

Coloration and Mimicry Cryptic Coloration Aposematic Coloration Batesian Mimicry Mullerian Mimicry Batesian Mimicry

Herbivory A +/- interaction in which an herbivore eats parts of a plant or alga Predator mechanisms: include specialized teeth or digestive systems, enhanced senses, and selective eating (leaving part of plant behind) Similar defense mechanisms as with predation, but chemical defenses and coloration are most common

Symbiosis Symbiosis Mutualism: an interaction that benefits both species; a +/+ interaction –acacia trees and ants Commensalism: an interaction between species where one benefits while the other is neither harmed nor helped; a +/0 interaction –egrets and water buffalo Parasitism: a +/- interaction in which one organism (parasite) derives nourishment from another (host); pathogen = lethal –Tape worm and human Can you think of any additional examples (at least 1 of each)? Mutualism Commensalism

Mutualism

Which forest is more diverse? Explain your rationale.

Which forest is more diverse? Species diversity has 2 components: ① ① Species richness: total number of different species ② ② Relative abundance: proportion each species represents Answer = Ecologists would say community 1 has greater species diversity Species Diversity

Compare and contrast food webs and food chains. –What is the value of using each as a tool?

Trophic Structure Feeding relationships Transfer of energy up trophic levels –Primary producers –Primary consumers –Secondary consumers –Tertiary consumers –Quaternary consumers Trophic Levels

Identify a 6 level food chain in this Antarctic marine food web. Do you think this type of food chain is common? Why or why not.

Analyze the following graphs to define what a keystone species is.

Dominant and Keystone Species Dominant species: most abundant and have the most biomass, impact on a community can vary Keystone species: not abundant, but play critical role because of the niche they occupy within the community –examples include sea stars and sea otters

Disturbance An event that changes a community by removing organisms and altering resources –Examples include a storm, fire, flood, drought, overgrazing, or human activity Can have long-term, positive effects Prairie Disturbance Recovery

Succession Transition in the species composition of a community overtime Primary succession: begins in a lifeless area with no soil, example – a new volcanic island Secondary succession: when an existing community has been cleared by some disturbance, leaves soil intact Ecological Succession

Applying the Concepts… Two identical plots were staked out. Each included a few sagebrush plants and numerous wildflowers (5 different species of equal proportions). One plot was enclosed to keep out kangaroo rats, the most common grain-eaters of the area. After 2 years - in the fenced plot 4 of the wildflower species were no longer present, but 1 species had dramatically increased. There was no change in the control plot. USING THE PRINCIPLES OF ECOLOGY… –Propose a hypothesis to explain her results. –What additional evidence would support your hypothesis?

Applying the Concepts… Sometime in 1986, near Detroit, a freighter pumped out water ballast containing larvae of European zebra mussels. The molluscs multipled wildly, spreading through Lake Erie and entering Lake Ontario. In some places, they have become so numerous that they have blocked the intake pipes of power plants and water treatment plants, fouled boat hulls, and sunk buoys. USING THE PRINCIPLES OF ECOLOGY… –What makes this kind of population explosion occur? –What might happen to native organisms that suddenly must share the Great Lakes ecosystem with zebra mussels? –How would you suggest trying to solve the mussel population problem?