Chapter 54 Community Ecology

Community Ecology The study of the interactions between the species in an area.

Interspecific Interactions Interaction between species. May be positive, negative, or neutral (in regards to fitness) Ex: Predation Mimicry Competition Symbiosis

Predation (+/-) Predator and prey relationships. Ex – Lynx and Hares

Herbivory (+/-) When an organism eats parts of a plant or algae. Herbivore – may have special adaptations to find their prey. Plants – may have adaptations to avoid being eaten.

Predation/Herbivory Often results in interesting defenses or adaptations. Ex: Cryptic coloration Aposematic coloration

Cryptic Coloration A passive defense where the prey is camouflaged against its environment.

Aposematic Coloration The use of conspicuous colors in toxic or unpalatable organisms to warn off predators. poison arrow frogs

Mimicry Defense mechanism where the mimic has a resemblance to another species, the model. Types: Batesian Müllerian

Batesian Mimicry Palatable species mimics an unpalatable model. Hawk moth larva Snake

Müllerian Mimicry Two unpalatable species resemble each other. Yellow Jacket Cuckoo Bee

Competition When two species rely on the same limiting resource. Intraspecific competition usually more severe than Interspecific competition. Why?

Competitive Exclusion Principle Predicts that two species with the same exact requirement cannot co-exist in the same community. The better adapted species will survive and the less adapted will go extinct.

Think, Pair, Share Discuss if the Competitive Exclusion Principle explain the spacing of fast food restaurants on the “strip” in most towns.

Ecological Niche The sum of a species’ use of the biotic and abiotic resources in its environment is called the species’ ecological niche. How a species “makes its living” in its ecosystem. Species can not have niche overlap, the Competitive Exclusion Principle

Niche Types 1. Fundamental - what a species is theoretically capable of using. 2. Realized - what a species can actually use.

Think, Pair, Share Again in terms of fast food restaurants, explain the concept of a fundamental vs. realized niche.

Resource Partitioning A way that species avoid niche overlap by splitting up the available resources. Ex: Anolis lizards

A. distichus A. insolitus

7 species live in close proximity, all feed on insects, but since they each perch in a different area, their niches overlap less (resource partitioning)

Symbiosis When two different species live together in direct contact. Types: 1. Parasitism 2. Commensalism 3. Mutualism

Parasitism (+/-) Parasite harms the host. Parasites may be external or internal. Well adapted parasites don't kill the host. https://www.youtube.com/watch?v=uvdiYg6ZN-U Sci-Show Parasites

Commensalism (+/o) One partner benefits while the other is unchanged. Ex. – Cattle and Egrets

Mutualism (+/+) Both partners benefit from the interaction. Ex: Pollinators and flowers Acacia Tree and Ants

Species with large impacts Some species have larger impacts on a community structure than others. Ex: Dominant Species Keystone Species Foundation Species

Dominant Species A species that is the most abundant or has the highest biomass in a community. Has a major effect on a community both biotically and abiotically.

Reason for Dominance? Best Competitor? Best in avoiding predators and disease? Invasive species may fit the last explanation.

Example Chestnuts – used to make up to 40% of the forest. Lost between 1910-1950 because of fungus disease. Major impact on wood and nut industries.

Response Some tree species increased in abundance to fill the gap. Mammals and birds did OK. 7 species of insects went extinct.

Keystone Species Not a dominant species, but has a major impact in the community structure. Often a top predator that controls the numbers of other species. Ex. Sea Otters

Foundation Species Species that cause physical changes in the environment that affect others. Ex. Beavers, Bison, Black Rush

https://www.youtube.com/watch?v=ysa5OBhXz-Q How wolves change rivers

Succession Changes in species composition over time.

Succession Stages Climax Community - An ecological community in which populations of plants or animals remain stable and exist in balance  with each other and their environment.

Succession Types 1. Primary 2. Secondary

Primary Succession Succession with only abiotic materials as the starting substrate Ex: volcanic islands glaciated areas road cuts

Secondary Succession Succession with biotic materials (living or dead) as the starting substrate Ex: Cutting down a forest Forest fire Tornado/storm damage

Steps of Succession Pioneer Species – the first organisms to appear in the area in primary succession Usually moss or lichens

What do Pioneer Species Change? Enrich the soil – as generations die, their remains decompose and add nutrients to the soil (often N). The soil is now able to support a greater variety of species such as grasses and small shrubs.

Which occurs faster, primary or secondary succession? What can you do to speed up succession?

Point If you understand the causes and controlling factors of succession, you can manipulate them.

Some points about Succession The Organisms are changing in the area over time. General pattern is an increase in biodiversity. The Climate of the area is NOT changing over time.

Other Changes Soil – becomes richer in N, more depth, better water retention etc. Light – can decrease at ground level because of shading by taller plants.

Summary Know the various types of interspecific interactions. Know the Competitive Exclusion Principle and Niche Concept. Know Species with large impacts.

Summary Know some examples and causes of succession.