chapter 57 community of ecology Flashcards
Biological Communities
Community Species that occur at any particular locality Characterized by Species richness Number of species present Primary productivity Amount of energy produced Interactions among members govern many ecological and evolutionary processes
Two views of structure and functioning of communities
Individualistic concept: a community is nothing more than an aggregation of species that happen to occur together at one place
Holistic concept: a community is an integrated unit; superorganism – more than the sum of its parts
Most ecologists today favor the individualistic concept
In communities, species respond independently to changing environmental conditions
Community composition changes gradually across landscapes
Sometimes the abundance of species in a community does change geographically in a synchronous pattern
Ecotones: places where the environment changes abruptly
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Ecological Niche
Niche: the total of all the ways an organism uses the resources of its environment Space utilization Food consumption Temperature range Appropriate conditions for mating Requirements for moisture and more
Interspecific competition
Occurs when two species attempt to use the same resource and there is not enough resource to satisfy both
Fundamental niche Entire niche that a species is capable of using, based on physiological tolerance limits and resource needs Realized niche Actual set of environmental conditions, presence or absence of other species, in which the species can establish a stable population Other causes of niche restriction Predator absence or presence Absence of pollinators Presence of herbivores
Principle of competitive exclusion
If two species are competing for a limited resource, the species that uses the resource more efficiently will eventually eliminate the other locally
G.F. Gause’s classic experiment on competitive exclusion using three Paramecium species shows this principle in action
Resource partitioning among sympatric lizard species
Subdivided niche to avoid direct competition
Resource partitioning is often seen in similar species that occupy the same geographic area
Thought to result from the process of natural selection
Character displacement
Differences in morphology evident between sympatric species
May play a role in adaptive radiation
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Predator–Prey
Predation
Consuming of one organism by another
Predation strongly influences prey populations
Prey populations can have explosions and crashes
White-tailed deer in Eastern U.S.
Introduction of rats, dogs, cats on islands
New Zealand: Stephen Island wren extinct because of a single cat
Predation and coevolution
Predation provides strong selective pressure on the prey population
Features that decrease the probability of capture are strongly favored
Coevolution race may ensue
Plants adapt to predation (herbivory) by evolving mechanisms to defend themselves
Chemical defenses: secondary compounds
Oils, chemicals to attract predators to eat the herbivores, poison milky sap, and others
Herbivores coevolve to continue eating the plants
Chemical defenses in animals
Monarch butterfly caterpillars feed on milkweed and dogbane families
Monarchs incorporate cardiac glycosides from the plants for protection from predation
Butterflies are eaten by birds, but the Monarch contains the chemical from the milkweed that makes the birds sick
Defensive coloration
Insects and other animals that are poisonous use warning coloration
Organisms that lack specific chemical defenses are seldom brightly colored
Camouflage or cryptic coloration help nonpoisonous animals blend with their surroundings
Camouflaged animals do not usually live together in groups
Mimicry allows one species to capitalize on defensive strategies of another
Resemble distasteful species that exhibit warning coloration
Mimic gains an advantage by looking like the distasteful model
Batesian mimicry
Mimics look like distasteful species
Müllerian mimicry
Several unrelated but poisonous species come to resemble one another
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Species Interactions
Symbiosis 2 or more kinds of organisms interact in more-or-less permanent relationships Potential for coevolution Three major types of symbiosis Commensalism Mutualism Parasitism
Commensalism benefits one species and is neutral to the other
Spanish moss: an epiphyte hangs from trees
Mutualism benefits both species Coevolution: flowering plants and insects Ants and acacias Acacias provide hollow thorns and food Ants provide protection from herbivores
Parasitism benefits one species at the expense of another
External parasites
Ectoparasites: feed on exterior surface of an organism
Parasitoids: insects that lay eggs on living hosts
Wasp, whose larvae feed on the body of the host, killing it
Internal parasites
Endoparasites live inside the host
Extreme specialization by the parasite as to which host it invades
Structure of the parasite may be simplified because of where it lives in its host
Many parasites have complex life cycles involving more than one host
Ecological processes have interactive effects
Predation reduces competition
Predators choice depends partly on relative abundance of the prey options
Superior competitors may be reduced in number by predation
This allows other species to survive when they could have been outcompeted
Keystone species
Species whose effects on the composition of communities are greater than one might expect based on their abundance
Sea star predation on barnacles greatly alters the species richness of the marine community
Keystone species can manipulate the environment in ways that create new habitats for other species
Beavers
