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Species interactions A predator is an organism that feeds directly upon another living organism, whether or not it kills the prey in doing so Prey most successfully on slowest, weakest, least fit members of target population Reduce competition, population overgrowth, and stimulate natural selection Co-evolution Coevolution – “Arms Race” Natural selection promotes traits that help prey escape predation It also promotes traits that make predators more successful at capturing prey Types of predation Population dynamics Herbivores can have dramatic effects on plant populations. Major basis of bio-control Prickly pear introduced into Australia in 1839 By 1925 was in 240,000 km2 Released moth from S.America in 1925 Big effect Prey adaptation to avoid predation Prey and predators are not evolutionarily passive There exist a large suite of prey responses/adaptation which decreases the likelihood of being consumed Such variety, and commoness of these traits is evidence of the strong selective pressure of predation on evolution Prey Defenses Chemical Camouflage Warning coloration Mimicry Displays Morphology Masting Chemical Chemical defenses Can be used in attack, or following consumption Cane Toad and native animals Naïve predators Camouflage Crypsis and catalepsis Coloration and markings to blend in to the surroundings Development of a frozen posture Warning coloration Aposematic coloration Mimicry - Batesian Monarch-Viceroy Mimicry of a unpalatable species (MODEL) by a palatable one (MIMIC) Mimic success is dependent upon mimic:model abundance High mimic abundance can harm model If predators learn Mimicry Batesian mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species Mimicry Mullerian Mimicry - Two unpalatable species evolve to look alike Mimicry - Mullerian Evolutionary convergence of unpalatable (or dangerous) species to look and act the same Yellow-black striping in wasps and bees There are often Batesian mimics of Mullerian mimicry complexes! Many harmless yellow/black flies Intimidation displays Many organisms can “increase” size in response to danger Give appearance of being larger – and thus bigger threat Can also just startle predator – deters ambush predators. Masting Synchronous production of many progeny by all individuals in a population Saturates predators High juvenile mortality, but less than if only a few offspring produced Morphological Physical deterrent to predator Can be induced Phenotypic plasticity Daphnia Spikeless vs Spiked forms Chemically induced Behavior to avoid defense Predator Responses Predator adaptations include stealth, camouflage, and ways to avoid chemical repellents Summary of prey defenses Variety of mechanisms of defense Chemical Morphological Behavioral Same sort of idea as in plant defense Common evolutionary pressure to avoid consumption Not every species has every (or any) defenses Evolutionary constraints Trade-offs Symbiosis Symbiosis - Intimate living together of members of two or more species Commensalism - One member benefits while other is neither benefited nor harmed Mutualism - Both members benefit Parasitism - One member benefits at the expense of other Mutualism Both species benefit Mutualisms can be obligate or facultative Some are more intimate relationships than others Yucca and yucca moth An obligatory mutualism Each species of yucca is pollinated by only one species of moth Moth larvae can grow only in that one species of yucca Rhizobium Acacia and ants Ants get nectar and a place to live Ants provide protection and reduction in competition Cleaner fish Leaf-cutter ants Mycorrhizae Association between plant and fungus Can strongly influences growth and survival Commensalism Commensalism Difficult to distinguish Can cross over into mutualism or parasitism or have characters of both Parasitism Parasites drain nutrients from their hosts and live on or in their bodies Natural selection favors parasites that do not kill their host too quickly Have complex life cycles Types of species interactions Interactions between processes Different processes can be going on at same time Predation and parasitism can reduce competition Species may have indirect effects on each other Think back to deer/tick/acorn story Indirect effects Ants and rodents live together and both eat seeds Rodents are removed Ants do well at first, then decline in number Keystone Species Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance Keystone Species Ecosystem engineers