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Community Interactions Chapter 53 Community Ecology • Community – all the species in a given location at a given time • Habitat the physical environment they live in, e.g. Redwood forest • Niche – how a species uses the resources in its habitat – Builds nest in tree top vs. lower branches • Similar species coexist by Niche specialization. Fig. 32.8a Fig. 32.8b Energy Transfer in Ecosystems Food / Energy Pyramid Primary Consumers eat producers, incorporating the energy into the next level. • Only 10 % of energy consumed moves to next level – Animals loose 90% of the energy at each level – Why are Big Fierce Animals so Rare?? • Consumers are Heterotrophs Simple Food Chains Trophic Levels Both Marine and Terrestrial Food Webs • Energy transfer follows trophic levels • Many animals eat at several trophic levels • Omnivores: like most of us – At salad bar you’re a herbivore – Eating a burger makes you a carnivore marsh hawk Higher Trophic Levels Sampling of connections in a Tall grass prairie food web crow upland sandpiper garter snake frog weasel spider Second Trophic Level sparrow earthworms, insects First Trophic Level badger coyote prairie vole grasses, composites pocket gopher ground squirrel Plant Community structure • Individualistic view (Gleason) • Interactive view (Clements) • Whittaker’s test • Plant communities are loose associations without discrete boundaries Competitive Exclusion • The more similar two species’ niches the more they compete. • No two species can share the exact same niche- one dies out. • Species evolve to diverge their niches by Resource Partitioning Paramecium caudatum Paramecium aurelia Competitive exclusion Fig. 32.10 Follow up: • Gause next added Paramecium aurelia with P. bursaria • They used the resources differently and both survived at lower levels. • Resource partitioning species evolve to avoid competition. – why? Fig. 32.11 Resource Partitioning Competition for space on the rocks Weak competitors stuck higher up in the intertidal Bristly foxtail Indian mallow Smartweed • Nuthatch crawls down the tree’s bark eating insects • Brown Creeper crawls up the same trees eating insects Caulerpa taxifolia suffocating a marine ecosystem • Introduced species often out compete natives • Lack predators that the natives have coevolved with Character Displacement Two species with same Beak size can not Coexist on same island One adaptive result of resource partitioning Types of Interspecific Interactions Species A Species B Commensalism + 0 Mutualism + + Competition - - Predation + - Parasitism + - • Commensalism Predator & Prey a Mutualism? Canadian lynx (dashed line) Snowshoe hares (solid line) Keystone species • Pisaster (Sea Star) defends tide pool from being taken over by mussels, barnacles. Sea Otters maintain Kelp forest • Otters are a Keystone species • Kelp are the base of the community • Urchins eat kelp • Otters eat urchins • Otter numbers along California are dropping. • Alaska- Orcas starting to eat otters, because seal numbers are dropping • No fish for seals • Kelp forests disappearing Species Richness • More energy available (productivity) the species can exist. • The larger the community size the more species can be supported. Number of species of ants Number of species of breeding birds Species Richness by Latitude Island Biogeography Ideas: • Size of island influences survival rate – Larger islands sustain more species • Nearness to other island influences immigration rate – Near islands have more species than distant islands • “Islands” are any isolated habitat Island Biogeography • Larger islands sustain more species Bio Reserve Model • Core - strict preserve, research. • Inner Buffer - hiking, Some commercialization. • Outer buffer - (may not even be part of park) camping, concessions, grazing timber, agriculture. – Core • Round parks have less edge effect Core – Higher per cent of park is in core area Fig. 23.26, p. 618 Edge effect • Natural vs. Artificial edges Bio Reserve Model • Corridors connect core areas from park to park forming land bridges • Our national Forests serve this role in many areas of the west. • Few Lager rounded parks, better than many smaller isolated parks fpr species richness Biosphere Reserve Core area Inner Buffer Outer Buffer Fig. 23.27, p. 620 Hilo Kona Naalehu One Species Two Species Overlap Three Species Overlap Existing Nature Reserves Fig. 23.28, p. 621 Succession: How the Community Structure changes over time • Primary Succession: starts with no soil, just bare exposed rock – Progresses in stages until long term climax stage • Secondary Succession starts with the climax vegetation type – Disturbance (fire) resets timeline – Progresses in stages back to climax. Cottonwood and Alders Spruce moves in Spruce and Hemlock Climax Vegetation Fire is a common disturbance in grasslands Fire Cycle • Community most likely to burn in many areas. • Many homes now built in these areas. • Early succession after fire, nutrient limited, mostly annuals and forbs (herbs) wildflowers. • Many species are sprouters– Burl survives fire, seeds out new shoots afterwards • new growth may be very high in protein 14%, deer and other animals rely on this growth. • some closed cone pines - need fire to release seeds. • Fire follower annual- seeds in soil seed bank germinate and predominate first few years after fire • Shrub canopy closes in about 6 years Fire poppies in burn area Madrones sprout from burl Ceanothus seedlings sprout after fire 1 month post fire Schmidts, M.J., D.A. Sims, J.A. Gamon California State University, Los Angeles, CA http://vcsars.calstatela.edu/eas_00/miriam/miriam_esa_00.html First spring 3 years post fire 20 and 40 years post fire Aposematic Coloration Warning I’m poisonous! Batesian Mimicry I only look dangerous Mullerian Mimicry We both are dangerous Camouflage I look like the background