In an evolutionary arms race, natural selection progressively escalates the defenses and counterdefenses of the species. The thick calcareous shells of many marine mollusks and the powerful drilling appendages and musculature of their predators are thought to have coevolved through this process of escalation. A similar example of coevolution has occurred in the endemic mollusks and crabs in Lake Tanganyika. The mollusks in this lake have much thicker shells than other freshwater mollusks, and the endemic crab that feeds on them has much larger chelae (pincerlike claws) than other freshwater crabs. Differences between these mollusks and crabs and the freshwater species throughout the world to which they are related appear to be due to coevolution rather than any unique nutrient or mineral conditions in this lake.
Transfer-of-energy-through-an-ecosystemFigure 2: Transfer of energy through an ecosystem. At each trophic level only a small proportion of …[Credits : Encyclopædia Britannica, Inc.]
Generalized-aquatic-food-webFigure 1: Generalized aquatic food web. Parasites, among the most diverse species in the food web, …[Credits : Encyclopædia Britannica, Inc.]
Male-resplendent-quetzal-or-resplendent-trogonMale resplendent quetzal, or resplendent trogon (Pharomachrus mocinno).[Credits : Michael & Patricia Fogden]
Parasitoids-which-parasitize-other-arthropods-by-depositing-eggs-in-theFigure 2: Parasitoids, which parasitize other arthropods by depositing eggs in the pupae, larvae, …[Credits : Encyclopædia Britannica, Inc.]
DOrbignys-round-eared-bat-capturing-a-katydid-in-flightD’Orbigny’s round-eared bat (Tonatia silvicola) capturing a katydid in flight.[Credits : © Merlin D. Tuttle, Bat Conservation International—Photo Researchers, Inc.]
Silky-anteater-extending-its-long-narrow-tongue-which-it-usesSilky anteater (Cyclopes didactylus) extending its long, narrow tongue, which it uses to …[Credits : Gunter Ziesler/Bruce Coleman Ltd.]
Coevolution-between-the-yucca-moth-and-the-yucca-plantCoevolution between the yucca moth and the yucca plant. (Top) A female yucca moth …[Credits : Photographs, © Robert and Linda Mitchell]Coevolution between the yucca moth and the yucca plant. (Top) A female yucca moth …[Credits : Photographs, © Robert and Linda Mitchell]
Coevolution-of-one-species-with-many-speciesCoevolution of one species with many species. (Top) European cuckoo (Cuculus canorus) …[Credits : John Markham/Bruce Coleman Ltd.]Coevolution of one species with many species. (Top) European cuckoo (Cuculus canorus) …[Credits : John Markham/Bruce Coleman Ltd.]
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