Chapter 54 Communities
Overview: A Sense of Community • A biological community is an assemblage of populations of various species living close enough for potential interaction
Ecologists call relationships between species in a community interspecific interactions • Examples are competition, predation, herbivory, and symbiosis (parasitism, mutualism, and commensalism) • Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or no effect (0)
Niche: “A place in nature” • Niche: the functional role of a particular species in an ecosystem • A niche is how an organism lives, its “job” • Fundamental niche: the entire range of conditions an organism is potentially able to live in • Realized niche: the part of the fundamental niche the organism actually lives in
Competition Shapes Communities • Competition: a biological interaction in which two species use the same resource.
Competition can limit how species use resources • If species can’t evolve because of competition, they will go extinct • Competitive exclusion: the elimination of a competing species • Gause Experiment
Resource partitioning~ sympatric species consume slightly different foods or use other resources in slightly different ways Competition evidence Ex: Anolis lizard sp. perching sites in the Dominican Republic
How Organisms Interact • Interactions among species are the result of a long evolutionary history. • Coevolution: Back-and- forth evolutionary adjustments between interacting members of an ecosystem • Predation: the act of one organism feeding on another.
Prey display various defensive adaptations • Behavioral defenses include hiding, fleeing, forming herds or schools, self-defense, and alarm calls • Animals also have morphological and physiological defense adaptations • Cryptic coloration, or camouflage, makes prey difficult to spot
Fig. 54-5 (a) Cryptic coloration Canyon tree frog (b) Aposematic coloration Poison dart frog (c) Batesian mimicry: A harmless species mimics a harmful one. Hawkmoth larva (d) Müllerian mimicry: Two unpalatable species mimic each other. Cuckoo bee Green parrot snake Yellow jacket
Fig. 54-5a Cryptic coloration (a) Canyon tree frog
Animals with effective chemical defense often exhibit bright warning coloration • Predators are particularly cautious in dealing with prey that display such coloration
Fig. 54-5b Aposematic coloration (b) Poison dart frog
In some cases, a prey species may gain significant protection by mimicking the appearance of another species • In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model
Fig. 54-5c (c) Batesian mimicry: A harmless species mimics a harmful one. Hawkmoth larva Green parrot snake
In Müllerian mimicry, two or more unpalatable species resemble each other
Fig. 54-5d (d) Müllerian mimicry: Two unpalatable species mimic each other. Cuckoo bee Yellow jacket
Symbiosis: two or more species interact and live together • Mutualism: a symbiotic relationship where both organisms benefit.
Fig. 54-7 (a) Acacia tree and ants (genus Pseudomyrmex) (b) Area cleared by ants at the base of an acacia tree
Fig. 54-7a (a) Acacia tree and ants (genus Pseudomyrmex)
Fig. 54-7b (b) Area cleared by ants at the base of an acacia tree
Commensalism: symbiotic relationship where one organism benefits and the other is neither harmed nor helped • Parasitism: organisms feed on and live on/in another organism.
Energy considerations for communities • Trophic structure is the feeding relationships between organisms in a community • It is a key factor in community dynamics • Food chains link trophic levels from producers to top carnivores
Fig. 54-11 Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Herbivore Zooplankton Primary producers Plant Phytoplankton A terrestrial food chain A marine food chain
Food Webs • A food web is a branching food chain with complex trophic interactions
Fig. 54-12 Humans Smaller toothed whales Sperm whales Baleen whales Elephant seals Leopard seals Crab-eater seals Squids Fishes Birds Carnivorous plankton Euphausids (krill) Copepods Phyto- plankton
Species with a Large Impact • Certain species have a very large impact on community structure • Such species are highly abundant or play a pivotal role in community dynamics
Dominant Species • Dominant species are those that are most abundant or have the highest biomass • Biomassis the total mass of all individuals in a population • Dominant species exert powerful control over the occurrence and distribution of other species • Invasive species, typically introduced to a new environment by humans, often lack predators or disease
Keystone Species • Keystone species exert strong control on a community by their ecological roles, or niches • In contrast to dominant species, they are not necessarily abundant in a community
Ecosystems Change Over Time: in response to disturbances. • Succession: Predictable progression of species replacement within habitats. • Primary succession: succession occurs where plants have not grown before • Pioneer Species: new fast-growing plants that inhabit a new habitat. • Secondary succession: succession where plants have grown previously.