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Relationships in Ecosystems Types of ecological interactions predation parasitism competition mutualism commensalism symbiosis Competition – two species share a requirement for a limited resource reduces fitness of one or both species Predation – one species feeds on another enhances fitness of predator but reduces fitness of prey herbivory is a form of predation Parasitism – one species feeds on another enhances fitness of parasite but reduces fitness of host Mutualism – two species provide resources or services to each other enhances fitness of both species Commensalism – one species receives a benefit from another species enhances fitness of one species; no effect on fitness of the other species Symbiosis – two species live together can include parasitism, mutualism, and commensalism Predator-prey relationships Predation is a straight-forward interspecies population interaction. One species uses another as a food resource. Predators play an important role in controlling prey population numbers in some systems. In simple systems, the predator-prey relationship results in coupled population osscilations Classic example of predator-prey dynamics: Canadian lynx & snowshoe hare Coupled oscillation • prey numbers increase, predator numbers increase…to a point where the predation causes population decline in the prey item.. • Idealized predator-prey coupled dynamics. •It is important to note that in most systems the food web- the web of interactions among species- is far more complex than just a single predator and single prey item. The relationships can become quite complex and the “coupled” nature of the interaction becomes much more vague. Tactics of the Predator 1) Invisibility Cloak (cryptic coloration/ camouflage) http://www.youtube.com/watch?v=__XA6B41SQQ Tactics of the Predator 2) Patience is a Virtue (Hide and Wait) Tactics of the Predator 3) Death by Poisoning (Venoms) Tactics of the Predator 4) “Right this Way Please”: trap-doors, nets, and other deadly devices. Tactics of the Predator 5) Bigger, Badder, Faster 200 mph 700 lbs & built to kill What immortal hand or eye Could frame thy fearful symmetry? William Blake http://www.youtube.com/watch?v=DWsN63PRCW8 17,000 lbs, and perhaps as smart as you Tactics of the Predator Combinations- Invisibility Cloak; Patience; Bigger, Badder, Faster www.cheetah.org Responses of the Prey 1) Invisibility Cloak (cryptic coloration/ camouflage) Responses of the Prey 2) FLEE!!!! Responses of the Prey 3) Eat me and die (poisons and aposematic coloration): Responses of the Prey 4) “Shields up”: (armor): Responses of the Prey 5) “Who wants fetid flesh for dinner? Surely not a proud hunter like yourself” (play dead): Responses of the Prey 6) Mimicry: Batesian mimicry- looks like a toxic model- but is non-toxic Mullerian mimicry- looks like a toxic model- AND is toxic Responses of the Prey 6) Disguise: Responses of the Prey 6) Strength in Numbers: Herbivory, a special case of predation… Not really- herbivory involves the taking of plant material by an animal herbivore- is almost always non-fatal, and can sometimes be an advantage for the plant- or at least stimulate growth and promote community diversity... Herbivory generally becomes a problem when the ecological system is out of balance. E.g., invasive insects (gypsy moth)- or the loss of predators (white-tailed deer) Herbivore-plant relationships also can evolve into an “arms race” Plants evolve armor (thorns, spines, prickles), toxicity, implant cells with silica, and sometimes symbiotic relationships to defend foliage. Plants evolve thorns, animals evolve morphology and behavioral techniques to avoid thorns. Plants get taller, change canopy structure, animals get taller. Plants trick animals into doing their bidding: Plants want some parts eaten (fruits) for seed dispersal, only after the seed has matured (thus ripening), and plants do not want foliage eaten… The expense of herbivore defense is only worth it if the foliage is very valuable. Plants that live it harsh conditions, can’t afford to rebuild foliage, so develop defenses. Plants that grow in lush conditions, simply outgrow herbivores. Predator-prey relationships