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Interspecific Interactions Community Ecology

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Interspecific Interactions Community Ecology Community Ecology: Interactions THE REALM OF Community Ecology ECOLOGY Biosphere Community: All the populations of organisms • Biosphere Ecosystems living together in a given • Ecosystem place • Community Ecology: Characteristics: Interactions among Communities members of all of the • Biodiversity — species in a given – Species richness habitat. – Relative abundance Populations • Dominant vegetation • Stability/disturbance Organisms Redwood forest community The Niche Concept Why do species Y & Z coexist? • A population’s Habitat is the area in which it lives - “address” • Individualistic Hypothesis • Niche is a population’s total use of biotic and abiotic resources - “profession” – Y & Z need similar physical environment • Interactive Hypothesis • Multiple species within a community share habitat, but have different niches – Y needs Z – The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place Community Ecology Interspecific Interactions Interactions among Y Z members of all – – competition of the species in a given habitat. + – trophic — parasites / predators + o commensalism / facillitation A. Competitive Interactions B. Trophic Interactions Direct + + mutualism interactions C. Symbiotic Interactions o – amensalism D. Amensal Interactions Indirect interactions E. Facilitative Interactions Heyer 1 Community Ecology: Interactions A. Competition Example of Competitive Exclusion • Two barnacle populations require • Interspecific the same resource: Competition = when space two species compete • When Balanus is Species A Species B removed for the same limited Chthamalus resource spreads lower • Competitive – Fundemental niche Exclusion = the • When both species elimination of a compete Balanus displaces population due to Species A & B Barnacle populations illustrating Chthamalus competition Gause’s experiment w/ Paramecium competitive exclusion – Realized niche A. insolitus usually perches • in on shady branches. Anolis lizards A. ricordii A. ricordii A. insolitus A. alinigar A. christophei A. distichus A. cybotes • in A. cybotes A. etheridgei A. etheridgei shorebirds A. distichus perches on fence posts and other sunny surfaces. Figure 53.3 Competition & B. Trophic Quaternary consumers Character Displacement (Feeding) Carnivore • Geospiza spp. on islands of the Galapagos Carnivore Interactions Tertiary – allopatry 60 Los Hermanos consumers – sympatry 40 G. fuliginosa, Carnivore Carnivore 20 allopatric 0 Secondary consumers 60 Daphne Carnivore 40 Carnivore G. fortis, 20 allopatric 0 Primary consumers 60 Santa María, San Cristóbal Sympatric populations Herbivore Zooplankton 40 20 Primary 0 producers 8 10 12 14 16 Percentages of individuals in each size class Beak depth (mm) Plant Phytoplankton Figure 54.11 A terrestrial food chain A marine food chain Heyer 2 Community Ecology: Interactions Primary producers • Autotrophs (“self feeder”) – Photosynthetic plants, protists, bacteria – Chemoautotrophic bacteria • Obtain nutrients from nonliving materials – Inorganic compounds, minerals – CO2 to make organic backbones – Carbon fixation Decomposition is an important Consumers part of an ecosystem • Heterotrophs (“feed on others”) • Detritivores (detritus = decaying matter) Another level – Herbivores (“plant eater”) of consumer • Primary consumers: eat producers Recycle – Carnivores (“meat eater”) matter back into the • Secondary consumers: eat other abiotic world consumers Biomagnification A food web • Efficiency of transfer • Trophic patterns creates a food are rarely linear pyramid. • Typically ~10% [5– • Pyramid effect may 20%] efficiency of result in transfer between levels biomagnification of • I.e., to grow or environmental reproduce, 10x the contaminants. added energy & mass – Esp., compounds must be consumed. sequestered in fat or • Thus there must be a skeleton. lot of primary production to support long food chains. Heyer 3 Community Ecology: Interactions + – Predation and Adaptations • Mechanisms of defense have evolved in every species (size, flee, hide, venom) • Coevolution = a series of reciprocal adaptations in two species (a type of “arms race”) Coevolution: caterpillar and passionflower vine • Herbivory – One species (herbivore) eats part of a producer (prey) • Predation • Specialist herbivores acquire resistance to chemical – One species (predator) kills & defense of specific prey consumes another species (prey) Heyer 4 Community Ecology: Interactions + – + – Cryptic Coloration (Camouflage) Physical (Mechanical) defenses – Spines, bristles, shells • Repels predator • Makes hard to swallow/digest • Makes it too energetically expensive porcupine Works for both predator and prey – Cost > benefit for the predator Chemical defenses Sometimes defenses don’t work! • Chemical warfare – Predator learns to avoid species – Examples • Eucalyptus oil, oleander shrubs, stinkbugs, skunks, cane toads • Grasshopper mouse sticks stinky end into Stink beetle ground to munch head Heyer 5 Community Ecology: Interactions Mimicry • Color and patterns of warning coloration are copied (a) Cuckoo bee (b) Yellow jacket Figure 53.8 poison dart frog • In Müllerian mimicry, multiple noxious or unpalatable species resemble each other. Mimicry Mimicry • Color and patterns of warning coloration are copied • Color and patterns of warning coloration are copied Fly Stingless Wasp anterior end of a green parrot snake Yellow Beetle Jacket posterior end of a hawkmoth caterpillar • In Batesian mimicry, harmless species • In Batesian mimicry, harmless species mimic dangerous or toxic species. mimic dangerous or toxic species. Mimicry Mimicry • Color and patterns of warning coloration are copied • In Batesian mimicry, harmless species mimic dangerous or toxic species. • Only works if predators learn to avoid real danger! venomous coral snake non-venomous king snake • In Batesian mimicry, harmless species mimic dangerous or toxic species. Figs. 1.25–1.27 Heyer 6 Community Ecology: Interactions Figure 54.6 Mimic Octopus + – master of Batesian mimicry (a) Mimicking a venomous sea snake • Rapidly changes coloration, morphology & behavior (b) Mimicking (c) Mimicking a poisonous flounder a stingray https://www.youtube.com/watch?v=t-LTWFnGmeg Predation and Diversity Predation and Diversity • Keystone Predator • Keystone Predator = a species that = a species that reduces the reduces the population density population density of the strongest of the strongest competitors Pisaster sea star eating a mussel competitors Pisaster sea star eating a mussel • Predation can • Predation can help maintain help maintain species diversity species diversity C. Symbiosis • Partivory – One species (partivore) consumes part of another • Sym- : “together”; -bios: “living” species (host) without killing or consuming all of it • One species living in, or on, or in tight association with another species • Symbiont and Host • Three types of symbiosis – Parasitism + – – Commensalism + o – Mutualism + + Aedes aegypti feeding on human Heyer 7 Community Ecology: Interactions + – Parasitism Parasitism • Symbiont benefits at the expense of the host • Symbiont benefits at the expense of the host • Other kinds of parasite cost their host something else • E.g., “brood parasite”: Cuckoo “foster” their young in other • Trophic parasite feeds off tissues of host (partivore) species nests – Ectoparasites & Endoparasites – Not all partivores are parasites (symbionts)! tick + o Parasitoid Commensalism • Parasite or slow predator? – A “good” parasite does not kill its host • Parasitoid wasp stings & paralyzes spider — but does not kill it • Lays eggs inside spider • Wasp larvae hatch & consume living spider • Spider killed when larva metamorphose & emerge Eagles nesting in conifers • Symbiont has no significant effect on host + + + o? Mutualism Both symbiont & host benefit from the relationship Acacias & ants • Manta & remoras S. Am. Acacias provide shelter, nectar & antfood to harbor Pseudomyrmex ants • Is the effect of the symbiont on the host Ants defend the acacias from herbivores, really insignificant? pathogenic fungi, & competing vegetation Heyer 8 Community Ecology: Interactions + + Amensalism: Endosymbiotic A species is neither benefited nor harmed by another species, but the activity, metabolism or defenses of the Mutualism first species inhibits or eliminates the second species Harmful algal blooms (HAB) Termites & • Overgrowth of photosynthetic cyanobacteria or protists Corals & Trichonympha • Consumption of dO2, decreased light penetration, and/or Symbiodinium production of toxic metabolites impacts other aquatic spp. [Zooxanthellae] Amensalism: Competition or Amensalism? A species is neither benefited nor harmed by another species, but the activity, metabolism or defenses of the • If Balanus first species inhibits or eliminates the second species distribution is the Human amensalism same whether or not • Agricultural & urban development, and waste production Chthalamus is present, should it be • Negatively impact many species called a competitive or amensal interaction? Burrowing owls • Inhabit old tunnels of prairie dogs or ground squirrels in dry grasslands • Populations nation-wide threatened by habitat loss • Listed as endangered & CA Species Barnacle populations illustrating of Special Interest competitive exclusion Pathogens Facilitation • Microorganisms that cause disease • Growth of turf algae slows water flow rate • May be trophic or amensal enhanced recruitment by seagrass seeds – Sudden Oak Death (SOD) Heyer 9 .
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