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Chapter 45 Community Ecology

Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

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Page 1: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Chapter 45Community Ecology

Page 2: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

45.1 Fighting Foreign Fire Ants

• Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful stings

• Global trade and shipping brought fire ants to the US and to other countries around the world

• Fire ants have a negative impact on native species of plants, insects, birds, and other animals

Page 3: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Red Imported Fire Ants

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Communities

• Species interactions such as competition or predation are one focus of community ecology

• A community is all the species that live in a region

• Species interactions and disturbances can shift community structure (types of species and their relative abundances) in small and large ways

Page 5: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

45.2 Which Factors Shape Community Structure?

• Community structure refers to the number and relative abundances of species in a habitat

• Habitat• The type of place where a species normally lives

• Community• All species living in a habitat

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Species Diversity

• Communities vary in their species diversity

• Two components of species diversity:• Species richness: the number of species• Species evenness: the relative abundance of each species

Page 7: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Community Structure

• Many factors influence community structure• Abiotic factors such as climate• Gradients of topography• Species interactions (direct and indirect)

• Symbiosis refers to direct, long-term interactions:• Commensalism: One species benefits and the other is

neither benefited nor harmed• Mutualism: Both benefit• Parasitism: Parasite benefits, host is harmed

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Table 45-1 p810

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Commensalism

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Take-Home Message: What factors affect species in a community?

• The types and abundances of species in a community are affected by physical factors such as climate and by species interactions.

• A species can be benefited, harmed, or unaffected by its interaction with another species.

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45.3 Mutualism

• Mutualism is a species interaction in which each species benefits by associating with the other• Flowering plants and animal pollinators• Birds that disperse seeds• Lichens, mycorrhizae, and nitrogen-fixing bacteria that

help plants obtain nutrients• Animals share nutrients with mutualistic microorganisms in

their gut• Two species may protect one another

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Obligate Mutualism: Yucca and Moth

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Mutual Protection

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Take-Home Message: What are the effects of participating in a mutualism?

• A mutualism benefits both participants.

• In some cases, two species form an exclusive partnership. In others, a species provides benefits to, and receives benefits from, multiple species.

• Participating in a mutualism has both benefits and costs. Selection favors individuals who maximize their benefits while minimizing their costs.

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45.4 Competitive Interactions

• Resources are limited; individuals of different species often compete for access to them

• Interspecific competition hurts both species

• Competition among individuals of the same species is more intense than interspecific competition

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The Niche

• Each species requires specific resources and environmental conditions that we refer to as its ecological niche

• Both physical (abiotic) and biological (biotic) factors define the niche

• The more similar the niches of two species are, the more intensely the species will compete

Page 17: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Interspecific Competition

• Interference competition• One species actively prevents another from accessing a

resource

• Exploitative competition• Species reduce the amount of a resource available to the

other by using that resource

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Interference Competition

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Effects of Competition

• Competitive exclusion• When 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

• Competitors can coexist when their resource needs are not exactly the same• Competition suppresses growth of both species

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Competitive Exclusion in Paramecium

Stepped Art

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P. caudatum alone

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P. aurelia alone

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Both species together

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ANIMATED FIGURE: Competitive exclusion

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Competing for Pollinators

Mimulus Lobelia

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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 (directional selection)

• Example: Eight species of woodpecker in Oregon feed on insects and nest in hollow trees, but the details of their foraging behavior and nesting preferences vary

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Character Displacement

• Over generations, directional selection leads to character displacement – the range of variation for one or more traits is shifted in a direction that lessens the intensity of competition for a limiting resource

• Example: Where two species of salamanders coexist, differences in body length becomes more pronounced

Page 25: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Character Displacement in Salamanders

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ANIMATED FIGURE: Hairston's experiment

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Page 27: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Take-Home Message: What happens when species compete for resources?

• In some interactions, one species actively blocks another’s access to a resource. In other interactions, one species is simply better than another at exploiting a shared resource.

• When two species compete, selection favors individuals whose needs are least like those of the competing species.

Page 28: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

45.5 Predator–Prey Interactions

• Predation is an interspecific interaction in which one species (predator) captures, kills, and eats another species (prey)

• Relative abundances of predators and prey shift over time in response to species interactions and changing environmental conditions

Page 29: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Predator Responses to Changes in Prey Density

• Type I response (passive predators)• Number of prey killed depends on prey density

• Type II response• Number of prey killed depends on the predator’s capacity

to capture, eat and digest prey

• Type III response• Number of kills increases only when prey density reaches

a certain level

Page 30: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Responses of Predators to Prey Density

Page 31: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

A Type 2 Response

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Figure 45-9b2 p814

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ANIMATED FIGURE: Predator-prey interactions

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Page 34: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Cyclic Changes in Abundance

• Time lag in predator response to prey density can lead to cyclic changes in abundance

• When prey density is low, predators decline, prey are safer, prey numbers increase

• When prey density is high, predator numbers increase, prey numbers decline

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Canadian Lynx and Snowshoe Hare

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Predator and Prey

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Take-Home Message: How do predator and prey populations change over time?

• Predator populations show three general patterns of response to changes in prey density.

• Population levels of prey may show recurring oscillations.

• The numbers in predator and prey populations vary in complex ways that reflect the multiple levels of interaction in a community.

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45.6 An Evolutionary Arms Race

• Predators select for better prey defenses, and prey select for more efficient predators

• Prey defenses include exoskeletons, unpleasant taste, toxic chemicals or stings, and physical adaptations such as camouflage

Page 39: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Coevolution of Predators and Prey

• Predator and prey populations exert selective pressures on one another

• Genetic traits that help prey escape will increase in frequency

• Defensive improvements select for a countering improvement in predators

• Example: Spraying beetles and grasshopper mice

Page 40: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Defense and Counter Defense

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Some Physical Adaptations of Prey

• Warning coloration• Many toxic or unpalatable species have bright colors and

patterns that predators learn to avoid

• Mimicry• A harmless animal looks like a dangerous one

• Camouflage• Body shape, color pattern and behavior that make an

individual blend in with its surroundings

Page 42: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Warning Coloration and Mimicry

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Camouflage in Prey and Predators

Page 44: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Coevolution of Herbivores and Plants

• With herbivory, an animal feeds on plants

• Two defenses have evolved in response to herbivory:• Some plants withstand and recover quickly from the loss

of their parts• Some plants have physical deterrents (spines, thorns,

tough leaves); or chemical deterrents (secondary metabolites that taste bad or sicken herbivores)

Page 45: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Take-Home Message: How do predation and herbivory influence community structure?

• In any community, predators and prey coevolve, as do plants and the herbivores that feed on them.

• Defensive adaptations in plants and prey can limit the ability of predators or herbivores to exploit some species in their community.

Page 46: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

45.7 Parasites and Parasitoids

• With parasitism, one species (parasite) benefits by feeding on another (host), without immediately killing it

• Endoparasites such as parasitic roundworms live and feed inside their host

• An ectoparasite such as a tick feeds while attached to a host’s external surface

Page 47: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Endoparasites

Page 48: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Ectoparasites

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Parasite Diversity

• Parasitism has evolved in members of a diverse variety of groups

• Bacterial, fungal, protistan, and invertebrate parasites feed on vertebrates

• Lampreys attach to and feed on other fish

• Parasitic plants that withdraw nutrients from other plants

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Dodder: A Parasitic Plant

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Strangers in the Nest

• With brood parasitism, one egg-laying species benefits by having another raise its offspring• Examples: European cuckoo, cowbird

• One cowbird can parasitize 30 nests per season, decreasing the reproductive rate of the host species

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Cowbird with Foster Parent

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Parasitoids

• Parasitoids are insects that lay eggs in other insects

• Their larvae develop in the host’s body, feed on its tissues, and eventually kill it

• As many as 15 percent of all insects may be parasitoids

• Example: parasitoid wasps

Page 54: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Biological Pest Controls

• Some parasites and parasitoids are raised commercially for use as biological pest control agents

• Example: Parasitoid wasps lay eggs in aphids

• Introducing a species into a community as a biological control has both advantages and risks

Page 55: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Biological Pest Control Agent

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Take-Home Message: Effects of parasites, brood parasites, and parasitoids

• Parasites reduce the reproductive rate of host individuals by withdrawing nutrients from them.

• Brood parasites reduce the reproductive rate of hosts by tricking them into caring for young that are not their own.

• Parasitoids reduce the number of host organisms by preventing reproduction and eventually killing the host.

Page 57: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

45.8 Ecological Succession

• Ecological succession is a process in which one array of species replaces another over time

• It can occur in a barren habitat such as new volcanic land (primary succession) or a disturbed region in which a community previously existed (secondary succession)

Page 58: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Pioneer Species

• Primary succession begins when pioneer species such as lichens and mosses colonize a barren habitat with no soil

• Pioneer species are opportunistic colonizers of new or newly vacated habitats

• Pioneers help build and improve soil for later successional species

Page 59: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

Primary Succession: Alaska’s Glacier Bay

Page 60: Chapter 45 Community Ecology. 45.1 Fighting Foreign Fire Ants Native to Brazil, imported fire ants (Solenopsis invicta) nest in the ground and have painful

ANIMATED FIGURE: Succession

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