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CHAPTER 36 Communities and Ecosystems. Modules 36.1 – 36.4. Dining In. Wasps and Pieris caterpillars form an unusual three-step food chain The 4-mm-long wasp Apanteles glomeratus stabs through the skin of a Pieris rapae caterpillar and lays her eggs
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CHAPTER 36Communities and Ecosystems Modules 36.1 – 36.4
Dining In • Waspsand Pieris caterpillars form an unusual three-step food chain • The 4-mm-long wasp Apanteles glomeratus stabs through the skin of a Pieris rapae caterpillar and lays her eggs • The caterpillar will be destroyed from within as the wasp larvae hatch and nourish themselves on its internal organs
A female ichneumon will pierce the caterpillar and deposit her own eggs inside of the Apanteles larvae • Ichneumon wasps can detect when a Pieris caterpillar contains Apanteles larvae
Usually, only the chalcids will emerge from the dead husk of the caterpillar • Finally, yet another wasp, a chalcid, may lay its eggs inside the ichneumon larvae
A biological community derives its structure from the interactions and interdependence of the organisms living within it • Ecosystem functioning depends on the complex interactions between its community of organisms and the physical environment
36.1 A community is all the organisms inhabiting a particular area • All the organisms in a particular area make up a community • A number of factors characterize every community • Biodiversity • The prevalent form of vegetation • Response to disturbances • Trophic structure (feeding relationships) Figure 36.1
Biodiversity has two components • Species richness, or the total number of different species in the community • The relative abundance of different species • Biodiversity is the variety of different kinds of organisms that make up a community
STRUCTURAL FEATURES OF COMMUNITIES 36.2 Competition may occur when a shared resource is limited • Interspecific competition occurs between two populations if they both require the same limited resource • A population's niche is its role in the community • The sum total of its use of the biotic and abiotic resources of its habitat
Populations of two species cannot coexist in a community if their niches are nearly identical • The competitive exclusion principle Hightide Chthamalus Balanus Ocean Lowtide Figure 36.2
One of the populations, using resources more efficiently and having a reproductive advantage, will eventually eliminate the other • Natural selection may lead to resource partitioning • Competition between species with identical niches has two possible outcomes
36.3 Predation leads to diverse adaptations in both predator and prey • Predation is an interaction where one species eats another • The consumer is called the predator and the food species is known as the prey • Parasitism can be considered a form of predation
This process of reciprocal adaptation is known as coevolution • Example: Heliconius and the passionflower vine • As predators adapt to prey, sometimes natural selection also shapes the prey's defenses Eggs Sugardeposits Figure 36.3A
Mechanical defenses, such as the quills of a porcupine • Prey gain protection against predators through a variety of defense mechanisms
Animals with effective chemical defenses are often brightly colored to warn predators • Example: the poison-arrow frog • Chemical defenses are widespread and very effective Figure 36.3B
Example: the gray tree frog • Camouflage is a very common defense in the animal kingdom Figure 36.3C
Batesian mimicry occurs when a palatable or harmless species mimics an unpalatable or harmful one • The mimicry can even involve behavior • This hawkmoth larva puffs up its head to mimic the head of a snake Figure 36.3D
Müllerian mimicry is when two unpalatable species that inhabit the same community mimic each other • Example: the cuckoo bee and the yellow jacket Figure 36.3E
36.4 Predation can maintain diversity in a community • A keystone species exerts strong control on community structure because of its ecological role • A keystone predator may maintain community diversity by reducing the numbers of the strongest competitors in a community • This sea star is a keystone predator Figure 36.4A
Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp • Sea otters represent the keystone species Figure 36.4B