Chapter 41 Community Ecology (Sections 41.1 - 41.5)

41.1 Fighting Foreign Fire Ants Red imported fire ants, Solenopsis invicta, have a venomous sting, disrupt native wildlife communities, and are not controlled by pesticides Biological control involves phorid flies, specialized parasites (parasitoids) that kill their host by laying an egg in the ant’s tissues – the larvae eats its way through the fire ant and undergoes metamorphosis in its head community All species that live in a particular region

Phorid Fly and Fire Ant Phorid flies insert a fertilized egg into an ant’s thorax Parasitized ant that lost its head after a developing fly larva moved into it Figure 41.1 Red imported fire ants and their foes. Opposite, nest mounds of fire ants in a Texas pasture. A Phorid fly. This fly uses nia and as far north as Kansas and Delaware. the hooked extension on its abdomen to insert a fertilized egg into an ant’s thorax. B Parasitized ant that lost its head after a developing the fly larva moved into it. The larva will undergo metamor phosis to an adult inside the detached head.

41.2 Community Structure The type of place where a species normally lives is its habitat, and all species living in a habitat constitute a community Communities often are nested one inside another habitat Type of environment in which a species typically lives

Species Diversity Communities differ in their species diversity Species diversity has two components: Species richness (number of species) Species evenness (relative abundance of each species) Community structure is dynamic Species richness and evenness change over time

Factors Affecting Community Structure Community structure can change: As the community forms and ages As a result of natural or human-induced disturbances With changes in physical factors such as climate and resource availability Due to various types of species interactions

Species Interactions Species interactions can be mutually beneficial, mutually harmful, or benefit one species while harming the other Example: Commensal ferns attached to the trunk of a tree; the fern benefits from the light, and the tree is unaffected commensalism Species interaction that benefits one species and neither helps nor harms the other

Commensalism A tree with a commensal fern The fern benefits by growing on the tree, which is unaffected by the presence of the fern Figure 41.2 A tree with a commensal fern. The fern benefits by growing on the tree, which is unaffected by the presence of the fern.

Types of Two-Species Interactions Type of Interaction Species 1 Species 2 Commensalism Helpful None Mutualism Helpful Helpful Interspecific competition Harmful Harmful Predation, herbivory parasitism, parasitoidism Helpful Harmful

Symbiosis Symbiosis (“living together”) refers to a relationship in which two species have a prolonged close association Two species that interact closely for generations can coevolve – an evolutionary process in which each species acts as a selective agent on the other symbiosis One species lives in or on another in a commensal, mutualistic, or parasitic relationship

Key Concepts Community Characteristics A community consists of all species in a habitat A habitat’s history, its biological and physical characteristics, and interactions among species in the habitat affect the number of species in the community and their relative abundance

41.3 Mutualism In a mutualistic interaction, two species benefit by taking advantage of one another Example: Pollinators eat nectar and pollen, and plants receive pollen from other plants of the same species mutualism Species interaction that benefits both species

Mutualism and Coevolution In some mutualisms, neither species can complete its life cycle without the other Example: Yucca plants and the moths that pollinate them The moth matures when yucca flowers bloom Mouthparts of the female moth are specialized to collect yucca pollen Female flies to another flower, pierces its ovary, and lays eggs inside – fertilizing the yucca as she leaves Moth eggs develop into larvae in the ovary of the yucca

Yucca Plant and Yucca Moth Figure 41.3 Mutualism on a rocky slope of the high desert in Colorado. Only one yucca moth species pollinates plants of each Yucca species; each moth cannot complete its life cycle with any other plant. The moth matures when yucca flowers blossom. The female has specialized mouthparts that collect and roll sticky pollen into a ball. She flies to another flower and pierces its ovary, where seeds will form and develop, and lays eggs inside. As the moth crawls out, she pushes a ball of pollen onto the flower’s pollenreceiving platform. After pollen grains germinate, they give rise to pollen tubes, which grow through the ovary tissues and deliver sperm to the plant’s eggs. Seeds develop after fertilization. Meanwhile, moth eggs develop into larvae that eat a few seeds, then gnaw their way out of the ovary. Seeds that larvae do not eat give rise to new yucca plants.

Mutualism and Defense For some mutualists, the main benefit is defense Example: Sea anemone and anemone fish An anemone fish has a mucus layer that shields it from stinging cells (nematocysts) of a sea anemone Tentacles of the anemone protect the fish from predators The anemone fish chases away the few fishes that are able to eat sea anemone tentacles

Sea Anemone and Anemone Fish Figure 41.4 The sea anemone Heteractis magnifica has a mutualistic association with the pink anemone fish (Amphiprion perideraion). This tiny but aggressive fish chases away predatory butterfly fishes that would bite off tips of anemone tentacles. The fish cannot survive and reproduce without the protection of an anemone. The anemone does not need a fish to protect it, but it does better with one.

Mutualistic Microorganisms Mutualistic microorganisms help plants obtain nutrients: Nitrogen-fixing bacteria on roots of legumes (peas) provide the plant with extra nitrogen Mycorrhizal fungi living in or on plant roots enhance a plant’s mineral uptake Other fungi interact with photosynthetic algae or bacteria in lichens

41.4 Competitive Interactions Resources are limited and individuals of different species often compete for access to them (interspecific competition) Competition adversely affects both species interspecific competition Competition between two species

Ecological Niche Each species has an ecological niche defined by physical and biological factors; the more similar the niches of two species are, the more intensely they will compete An animal’s niches include the temperature range it can tolerate, species it eats, and places it can breed A flowering plant’s niche would include its soil, water, light, and pollinator requirements ecological niche All of a species’ requirements and roles in an ecosystem

Two Types of Interspecific Competition Exploitative competition: Two species reduce the amount of resources available to the other by using that resource Example: Deer and blue jays compete for acorns Interference competition: One species actively prevents another from accessing some resource Example: One species of scavenger will often chase another away from a carcass

Interference Competition Figure 41.5 Interspecific competition among scavengers.

Interference Competition A Golden eagle and a red fox face off over a moose carcass. B In a dramatic demonstration of interference competition, the eagle attacks the fox with its talons. After this attack, the fox retreated, leaving the eagle to exploit the carcass. Figure 41.5 Interspecific competition among scavengers. Stepped Art Fig. 41.5, p. 694

Effects of Competition Species compete most intensely when a shared resource is the main limiting factor for both Whenever two species require the same limited resource to survive or reproduce, the better competitor will drive the less competitive species to extinction in that habitat competitive exclusion Process whereby two species compete for a limiting resource, and one drives the other to local extinction

Experiment: Competitive Exclusion Two Paramecium species compete for the same food (bacteria) Each species thrives when grown alone When grown together, P. aurelia drove P. caudatum to extinction Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction.

Experiment: Competitive Exclusion

Experiment: Competitive Exclusion Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction. Fig. 41.6.1, p. 695

Experiment: Competitive Exclusion Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction. Fig. 41.6.2, p. 695

Experiment: Competitive Exclusion Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction. Fig. 41.6.3, p. 695

Experiment: Competitive Exclusion Time (days) population density Relative 0 4 8 12 16 20 24 P. caudatum alone Time (days) population density Relative 0 4 8 12 16 20 24 Both species together Time (days) population density Relative 0 4 8 12 16 20 24 P. aurelia alone Figure 41.6 Results of competitive exclusion between two Paramecium species that compete for the same food. When the two species were grown together, P. aurelia drove P. caudatum to extinction. Stepped Art Fig. 41.6, p. 695

ANIMATION: Competitive Exclusion To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

Resource Partitioning Resource partitioning is an evolutionary process by which species become adapted to use a shared limiting resource in a way that minimizes competition Example: Three plant species growing in the same field resource partitioning Species become adapted in different ways to access different portions of a limited resource Allows species with similar needs to coexist

Resource Partitioning Roots of each species take up water and mineral ions from a different soil depth Reduces competition among the species and allows them to coexist Figure 41.7 Resource partitioning among three annual plant species in a plowed but abandoned field. Roots of each species take up water and mineral ions from a different soil depth. This difference reduces competition among the species and allows them to coexist.

Character Displacement Directional selection occurs when species with similar requirements share a habitat and compete for a limiting resource, resulting in character displacement Example: Beak sizes in Galapagos finches character displacement Outcome of competition between two species Directional selection shifts the range of variation for one or more traits in a direction that lessens competition for a limiting resource

ANIMATION: Hairston's Experiment To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

ANIMATION: Resource Partitioning To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

41.5 Predation and Herbivory Predation and herbivory are short-term interactions in which one species obtains nutrients and energy by feeding on another predation One species (the predator) captures, kills, and eats another species (the prey)

Predator and Prey Abundance The abundance of prey species in a community affects how many predators it can support With some predators, such as web-spinning spiders, the proportion of prey killed is constant Usually, the number of prey killed depends on the time it takes predators to capture, eat, and digest prey

Predator and Prey Abundance (cont.) Predator and prey populations may rise and fall in cycles Example: Lynx and snowshoe hare populations rise and fall over a ten-year cycle Figure 41.8 Graph of the number of Canadian lynx (dashed line) and snowshoe hares (solid line), based on counts of pelts sold by trappers to Hudson’s Bay Company during a ninety-year period.

Lynx and Snowshoe Hare Figure 41.8 Graph of the number of Canadian lynx (dashed line) and snowshoe hares (solid line), based on counts of pelts sold by trappers to Hudson’s Bay Company during a ninety-year period.

Coevolution of Predators and Prey Predator and prey exert selection pressure on one another Predators exert selection pressure that favors improved prey defenses Improved prey defenses in turn exert selection pressure on predators to improve capture skills, and so on

Defensive Adaptations Defensive adaptations of prey include hard or sharp parts that make prey difficult to eat, and chemicals that taste bad or sicken predators Other adaptations trick or startle an attacking predator Well-defended prey often have warning coloration that predators learn to avoid, such as the black and yellow stripes of stinging wasps and bees

Defensive Adaptations (cont.) In a type of mimicry, prey masquerade as a species that has a defense that they lack Example: Some flies that can’t sting resemble stinging bees or wasps mimicry A species evolves traits that make it more similar in appearance to another species

Wasp and Mimic Figure 41.9 Mimicry. Some edible insect species resemble toxic or unpalatable species that are not closely related.

Predator Adaptations Predator adaptations include sharp teeth and claws Predators and prey may be coevolved for speed Example: cheetah and gazelle Both predators and prey use camouflage (a form, patterning, color, or behavior that allows them to blend into their surroundings) to avoid detection

Camouflage in Prey and Predators Figure 41.10 Camouflage in prey and predators.

Coevolution of Herbivores and Plants With herbivory, the number and type of plants in a community can influence the number and type of herbivores present herbivory An animal feeds on plant parts

Herbivores and Plants (cont.) There are two types of defenses against herbivory: Some plants have adapted to withstand and recover quickly from herbivory Other plants have traits such as spines, tough leaves, or toxins that deter herbivory Plant defenses favor adaptations in herbivores Example: Koalas have special enzymes to break down toxins in eucalyptus

ANIMATION: Predator-Prey Interactions To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE