CHAPTER 37 COMMUNITIES AND ECOSYSTEMS

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I. KEY TERMS at 49 min. Community Ecosystem Species – A group of organisms which can interbreed with each other and able to produce a fertile offspring. Habitat – the environment in which a species normally lives or the location of a living organism.

II. Characteristic Features of Communities Species diversity – The variety of different organisms that make a community up. Includes: species richness (the total number of different species) abundance – the density of living organisms. Species with larger impact Disturbance Trophic structure

Do you think these two communities have equal species diversity? Why? Why not? Which one would be a more stable community?

High species diversity makes the populations healthier, because: Can resist various natural disasters and fires better Viral, bacterial or fungal infections can be less harmful Can also resist extreme weather conditions better Diverse community of plants can give rise a more diverse community of animals, microbes, fungi etc.

Scientists are very concerned today, because most of the earth’s humans use only 3 main species of grains as food sources. Why can this be a major danger to the food supply of the planet? How can we decrease the risks?

III. Interspecific Interactions – Feeding Relationships Interspecific interactions – interactions between organisms of different species. These interactions can be beneficial or harmful for both or one of the organisms involved. During feeding relationships one rganism benefits, however, the other is harmed.

A. Predation – Predator kills the prey for feeding purposes.

Predators have acute senses to locate and identify prey, many also have structures such as teeth, claws, stingers, fangs and poison to catch the prey. Prey uses passive defenses, such as hiding and mimicry or active ones such as escaping and defending themselves.

Examples of prey capturing strategies: Concealment – camouflage themselves Infrared senses – especially for night animals (snakes, mosquitoes) Traps – spider webs Lures – angler fish, glow worms, some spiders Examples of predator avoidance: Mimicry Unpleasant chemicals and poisons (skunk, monarch butterfly) Visual deception (owl butterfly)

B. Herbivory – animals eating plants, however, they usually do not kill the plant.

Herbivores – animals that eat plants or algae. Herbivore adaptations: Chemical sensors Specialized teeth or mouth structures Specialized digestive track Coevolution of herbivores with plants can also occur – ants and acacia trees

IV. Interspecific Interactions -- Symbiosis Symbiotic relationships: permanent interaction between organisms. Three types of symbiosis: Parasitism – a form of exploitation, where one organism lives on or in an other organism and benefits for growth or reproduction from the other organism while it harms the other.

Mutualism – both species benefit from the association.

Commensalism – The presence of one species has a beneficial effect on the other, but is not itself affected by the association.

IV. Interspecific Relationship: Competition Intense competition exist within individuals of the same population because they compete for the exact same habitat and resources – intraspecific competition. Competition exist between different species. These species usually adopted through evolution to slightly different environments or the same resources but at different times – interspecific competition

Ecological niche – the functional position of an organism in its environment, comprising its habitat, resources and the periods of time during which it is active. The following are included in a niche: Physical conditions – Ex. Humidity, sunlight, temperature, salinity, pH, exposure, depth Resources offered by the habitat – Ex. Food sources, shelter, mating sites, nesting sites, predator avoidance. Adaptations for – locomotion, biorhythms, tolerance of physical conditions, defence, predator avoidance, reproduction, feeding.

Gause’s Competitive Exclusion Principle: Organisms occupying exactly the same niche cannot coexist because they will compete for the same resources. Frequently results in resource partitioning. Gray squirrel Red squirrel

Look at your picture of an owl. What is included in his niche? What other animal would this owl compete with? How would they resolve the competition

VII. Ecological Succession Ecological succession is the process by which communities in a particular area change over time. This takes place as a result of complex interactions between biotic and abiotic factors. The succession proceeds in stages until the formation of a climax community – the most stable community in the given environment until some disturbance occurs.

Primary succession (colonization of regions with no preexisting community): Bare rock → Lichens, bryophytes, annual herbs→ Grasses, small shrubs → Fast growing trees (ash) → slower growing broadleaf species (oak)

Secondary succession – takes place after a land clearance, tend to be faster than primary succession. The time scale depends on the type of species, climatic and soil factors: Primary bare earth → open pioneer community (annual grasses) → grasses and low growing perennials → shrubs and small trees → young broadleaved trees → mature woodland.

VIII. Food chains and food webs Food chains – linear sequences that link the various trophic levels (feeding levels) to each other. Its composition usually involves a producer primary consumer secondary consumer tertiary consumer (occasionally even a quaternary consumer) and decomposers can be included after every level.

Food webs – a more branched arrangement of feeding relationships. Includes the same levels that are included in a food chain.

IX. Species With Larger Impact Keystone species – organisms (usually predators) that exerts strong control on the community structure because of their role in the community. (ex. Sea otters) Dominant species – organisms that have the largest abundance in the community. (ex. Corn in a corn field)