Chapter 7 Community Ecology

Chapter Overview Questions  What determines the number of species in a community?  How can we classify species according to their roles in a community?  How do species interact with one another?  How do communities respond to changes in environmental conditions?  Does high species biodiversity increase the stability and sustainability of a community?

Core Case Study: Why Should We Care about the American Alligator?  Hunters wiped out population to the point of near extinction.  Alligators have important ecological role.

Core Case Study: Why Should We Care about the American Alligator?  Dig deep depressions (gator holes). Hold water during dry spells, serve as refuges for aquatic life. Hold water during dry spells, serve as refuges for aquatic life.  Build nesting mounds. provide nesting and feeding sites for birds. provide nesting and feeding sites for birds. Keeps areas of open water free of vegetation. Keeps areas of open water free of vegetation.  Alligators are a keystone species: Help maintain the structure and function of the communities where it is found. Help maintain the structure and function of the communities where it is found.

COMMUNITY STRUCTURE AND SPECIES DIVERSITY  Biological communities differ in their structure and physical appearance.

Fig. 7-2, p. 144 Short-grass prairie Desert scrub Tall-grass prairie Thorn scrub Thorn forest Deciduous forest Coniferous forest Tropical rain forest

Species Diversity and Niche Structure: Different Species Playing Different Roles  Biological communities differ in the types and numbers of species they contain and the ecological roles those species play. Species diversity: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness). Species diversity: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness).

Species Diversity and Niche Structure  Niche structure: how many potential ecological niches occur, how they resemble or differ, and how the species occupying different niches interact.  Geographic location: species diversity is highest in the tropics and declines as we move from the equator toward the poles.

Animation: Species Diversity By Latitude Animations/species_by_latitude.html

TYPES OF SPECIES  Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities. Native: those that normally live and thrive in a particular community. Native: those that normally live and thrive in a particular community.

Case Study: Species Diversity on Islands  MacArthur and Wilson proposed the species equilibrium model or theory of island biogeography in the 1960’s.  Model projects that at some point the rates of immigration and extinction should reach an equilibrium based on: Island size Island size Distance to nearest mainland Distance to nearest mainland

Animation: Area and Distance Effects Animations/species_equilibrium.html

SPECIES INTERACTIONS: COMPETITION AND PREDATION  Species can interact through competition, predation, parasitism, mutualism, and commensalism.  Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).

Animation: How Species Interact Animations/species_interactions.html

Resource Partitioning  Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species.

Niche Specialization  Niches become separated to avoid competition for resources.

Animation: Gause’s Competition Experiment Animations/gause_v2.html

SPECIES INTERACTIONS: COMPETITION AND PREDATION  Species called predators feed on other species called prey.  Organisms use their senses to locate objects and prey and to attract pollinators and mates.  Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.

PREDATION  Some prey escape their predators or have outer protection, some are camouflaged, and some use chemicals to repel predators.

Fig. 7-8a, p. 153 (a) Span worm

Fig. 7-8b, p. 153 (b) Wandering leaf insect

Fig. 7-8c, p. 153 (c) Bombardier beetle

Fig. 7-8d, p. 153 (d) Foul-tasting monarch butterfly

Fig. 7-8e, p. 153 (e) Poison dart frog

Fig. 7-8f, p. 153 (f) Viceroy butterfly mimics monarch butterfly

Fig. 7-8g, p. 153 (g) Hind wings of Io moth resemble eyes of a much larger animal.

Fig. 7-8h, p. 153 (h) When touched, snake caterpillar changes shape to look like head of snake.

ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION  New environmental conditions allow one group of species in a community to replace other groups.  Ecological succession: the gradual change in species composition of a given area

Animation: Succession Animations/succession.html

Primary Succession: Starting from Scratch Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment.  Primary succession begins with an essentially lifeless area where there is no soil in a terrestrial ecosystem Figure 7-11

Fig. 7-11, p. 156 Exposed rocks Lichens and mosses Small herbs and shrubs Heath mat Jack pine, black spruce, and aspen Balsam fir, paper birch, and white spruce forest community Time

Secondary Succession: Starting Over with Some Help Secondary succession: series of communities develop in places containing soil or sediment.  Secondary succession begins in an area where the natural community has been disturbed. Figure 7-12

Fig. 7-12, p. 157 Time Annual weeds Perennial weeds and grasses Shrubs and pine seedlings Young pine forest with developing understory of oak and hickory trees Mature oak-hickory forest

Can We Predict the Path of Succession, and is Nature in Balance?  The course of succession cannot be precisely predicted.  Previously thought that a stable climax community will always be achieved.  Succession involves species competing for enough light, nutrients and space which will influence it’s trajectory.

ECOLOGICAL STABILITY AND SUSTAINABILITY  Living systems maintain some degree of stability through constant change in response to environmental conditions through: Inertia (persistence): the ability of a living system to resist being disturbed or altered. Inertia (persistence): the ability of a living system to resist being disturbed or altered. Constancy: the ability of a living system to keep its numbers within the limits imposed by available resources. Constancy: the ability of a living system to keep its numbers within the limits imposed by available resources. Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance. Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance.

ECOLOGICAL STABILITY AND SUSTAINABILITY  Having many different species appears to increase the sustainability of many communities.  Human activities are disrupting ecosystem services that support and sustain all life and all economies.

Video: Bees Pollinating Videos/bumblebee.html

Video: Cliff Nesters Videos/cliff_birds.html

Video: Eagle Fishing Videos/eagle_fishing.html

Video: Grizzly Bear Feeding Videos/grizzly_feeds.html

Video: Migratory Birds Videos/migratory_birds.html

Video: Owl Hunting Videos/owl_hunts.html

Video: Pelican Colony Videos/pelican_colony.html

Video: Saguaros Videos/saguaros.html

Video: Wolf Pack Videos/wolf_pack.html