Community Structure and Biodiversity Chapter 40

Ecosystems Ecosystems vary in size. They can be as small as a puddle or as large as the Earth itself. Any group of living and nonliving things interacting with each other can be considered as an ecosystem.

Within each ecosystem, there are habitats These may also vary in size. A habitat is the place where a population lives. - Turlock habitat A population is a group of living organisms of the same kind living in the same place at the same time. Turlock humans All the different populations interact and form a community. City of Turlock

The community of living things interacts with the non-living world around it to form the ecosystem. The habitat must supply the needs of organisms, such as food, water, temperature, oxygen, and minerals. If the population's needs are not met, it will move to a better habitat. Two different populations can not occupy the same niche at the same time, however.

Community All the populations that live together in a habitat Habitat is the type of place where individuals of a species typically live Type of habitat shapes a community’s structure

Factors Shaping Community Structure Climate and topography Available foods and resources Adaptations of species in community Species interactions Arrival and disappearance of species Physical disturbances

Niche Sum of activities and relationships in which a species engages to secure and use resources necessary for survival and reproduction

Realized & Fundamental Niches - What??? Theoretical niche occupied in the absence of any competing species Realized niche Niche a species actually occupies Realized niche is some fraction of the fundamental niche

Species Interactions Most interactions are neutral; have no effect on either species Commensalism helps one species and has no effect on the other Mutualism helps both species

Species Interactions Interspecific competition has a negative effect on both species Predation and parasitism both benefit one species at a cost to another

Symbiosis Living together for at least some part of the life cycle Commensalism, mutualism, and parasitism are forms of symbiosis

Mutualism Both species benefit Many examples in nature Some mutualisms are obligatory; partners depend upon each other

Example: Mycorrhizae Obligatory mutualism between fungus and plant root Fungus supplies mineral ions to root Root supplies sugars to fungus

Example: Yucca and Yucca Moth Example of an obligatory mutualism Each species of yucca is pollinated only by one species of moth Moth larvae can grow only in that one species of yucca

Competition Interspecific - between species Intraspecific - between members of the same species Intraspecific competition is most intense

Forms of Competition Competitors may have equal access to a resource; compete to exploit resource more effectively One competitor may be able to control access to a resource, to exclude others

Competitive Exclusion Principle When two species compete for identical resources, one will be more successful and will eventually eliminate the other

Competitive Exclusion Expt. Protists - living together Paramecium caudatum Paramecium aurelia

Resource Partitioning Apparent competitors may actually have slightly different niches Species may use resources in a different way or time Minimizes competition and allows coexistence

Predation Predators are animals that feed on other living organisms Predators are free-living; they do not take up residence on their prey

Coevolution Natural selection promotes traits that help prey escape predation It also promotes traits that make predators more successful at capturing prey

Variation in Cycles An association in predator and prey abundance does not always indicate a cause and effect relationship Variations in food supply and additional predators may also influence changes in prey abundance

Species Interactions Canadian lynx (dashed lines) versus snowshoe hares (solid line)

Prey Defenses Camouflage Warning coloration Mimicry

Predator Responses Any adaptation that protects prey may select for predators that can overcome that adaptation Prey adaptations include stealth, camouflage, and ways to avoid chemical repellents

Parasitism Parasites drain nutrients from their hosts and live on or in their bodies Natural selection favors parasites that do not kill their host too quickly

Types of Parasites Microparasites Macroparasites Social parasites Parasitoids

Biological Controls Parasites and parasitoids are commercially raised and release in target areas as biological controls An alternative to pesticides Must be carefully managed to not upset natural balances

Study: Cowbirds Brown-headed cowbirds evolved in the Great Plains region of the U.S., living as commensalists with bison As they migrated along with the bison, the cowbirds learned to lay eggs in the nests of other birds Cowbird hatchlings push the “host” bird eggs out of the nest Today, cowbirds parasitize some 15 species of birds

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Change in the composition of different of species over time Succession Change in the composition of different of species over time

Pioneer Species Species that colonize barren habitats - first come, first served! Lichens, small plants with brief life cycles Improve conditions for other species who then replace them lose out to better adapted species who themselves lost out to even better adapted species.

Types of Succession Primary succession - new environments Secondary succession - communities were destroyed or displaced Following hurricanes After the tsunami

Climax Community Eventually we arrive at the climax community Stable array of species that persists relatively unchanged over time Succession does not always move predictably toward a specific climax community; other stable communities may persist Multiple outcomes.

Cyclic Changes DYNAMIC and STABLE Cyclic, nondirectional changes also shape community structure Tree falls cause local patchiness in tropical forests Fires periodically destroy underbrush in sequoia forests

Community Instability REMEMBER Disturbances can cause a community to change in ways that persist even if the change is reversed

Keystone Species A species that can dictate community structure Removal of a keystone species can cause drastic changes in a community; can increase or decrease diversity…

Lubchenco Experiment Periwinkles promote or limit diversity in different habitats Tidepools Rocks exposed at high tide

Species Introductions Introduction of a nonindigenous species can decimate a community Just recently Hawaii has introduces Sea Stars to control sea weed WHY? There are; No natural enemies or controls Can outcompete native species

Exotic Species Species that has left its home natural range and become established elsewhere Becomes part of its new community Can have beneficial, neutral, or harmful effects on a community…

Kudzu in Georgia

Kudzu in Georgia Imported for erosion control No natural herbivores, pathogens, or competitors Grows over landscapes and cannot be dug up or burned out May turn out to have some commercial use for humans

Caulerpa taxifolia

Caulerpa taxifolia Researchers developed a hybrid, sterile strain of this green alga - for fish tanks. Somehow it was released into the wild, where it reproduces asexually - down the drain!!! Thrives in varying conditions and emits a toxin that poisons invertebrates and fishes Illegal to import the “aquarium” strain into the U.S.

Rabbits in Australia Rabbits were introduced for food and hunting Without predators, their numbers soared Attempts at control using fences or viruses have thus far been unsuccessful

Biodiversity The sum of all species occupying a specified area during a specified interval, past and present

Diversity by Latitude Diversity of most groups is greatest in tropics; declines toward poles a) ant species b) breeding birds

Why Are Tropical Species Rich? Resources are plentiful and reliable Species diversity is self-reinforcing Rates of speciation are highest in the tropics

Surtsey: Volcanic Island Primary succession

Distance Effect The farther an island is from a mainland, the fewer species. WHY? Closer islands receive more immigrants Species that reach islands far from mainland are adapted for long-distance dispersal and can move on

Distance Effect

Endangered Species A species that is extremely vulnerable to extinction Habitat loss is putting major pressure on more than 90 percent of the endemic species that now face extinction

Conservation Biology Is a systematic survey of the full range of biological diversity Entails efforts to decipher biodiversity’s evolutionary and ecological origins Attempt to identify methods of maintaining and using biodiversity in ways that can benefit the human population Only real way to save the local ecosystem

Sampling of Current Species Diversity

Areas at Risk

Preserving Biodiversity Requires identifying and protecting regions that support the highest levels of biodiversity It is possible to protect a habitat and still withdraw resources in a sustainable fashion - but based on human nature it is a risky practice!