Species interactions Basic Reproductive Rate Ro lx mx Average number of daughters born to females of age x mx Competition Proportion surviving to age x lx For a cohort in a species with non overlapping generations N t 1 Ro N t Predation For a population with overlapping generations dN dt rN N t N 0 ert If growth is exponential density independent b d r don t change with N remember b d r the intrinsic rate of natural increase 1 2 Pairwise Species Interactions Interspecific Interactions Effect of individuals on other individuals or of populations on other populations of different species Competition interspecific Predation herbivory parasitism Mutualism Amensalism 0 Commensalism 0 humans cattle 3 4 True predators many hosts always lethal 5 52 19 52 21 6 Grazers many hosts rarely lethal Parasites one 1437 or nm few hosts rarely lethal 8 7 Parasitoids Fortunately human parasitoids seem to only occur in science fiction one host always lethal 9 Functional definitions 10 Connell s experimental studies of competition between barnacles Chthamalus Balanus High tide High tide Chthamalus realized niche Chthamalus fundamental niche Balanus realized niche Ocean 11 Low tide Ocean Low tide 12 Remove Balanus Chthamalus spreads into lower intertidal Remove Chthamalus Balanus does not spread upwards Balanus upper limit determined by physical stress Chthamalus lower limit determined by competition with Balanus Connell s experimental demonstration of asymmetric exploitative competition between barnacle species for space a limiting resource Chthamalus Balanus Space 13 14 3 Types of Competition More asymmetric competiton between ciliate protozoans 15 Exploitative two species compete for a resource that is limiting in short supply relative to their needs indirect Interference two species directly harm each other by toxic allelochemicals injury or wasting time increasing risk etc direct Predator mediated apparent two species decrease in each other s presence because they support the increased abundance or vigor of a common predator indirect Indirect interaction Predator mediated Apparent competition Wild salmon 16 Evolutionary consequences of competition Niche partitioning character displacement Number consumed Human fishers Seals terns Hatchery salmon Seed size 17 18 Partial niche overlap competition for seeds of intermediate size Finch A Finch B Seeds Species 2 Species 1 Number consumed Finch species once competed for seeds but natural selection for character displacement reduced competition for sympatric cooccurring populations Seed size 19 Finch A Little Seeds Finch B Big Seeds 20 Cleaning guiding etc Mutualism Mutualism is a type of interaction that is beneficial to both species involved It may be obligate or facultative It may be symbiotic or non symbiotic 21 22 Clown fish live in mutualistic symbiosis with sea anemone Clown fish mucus protects it from anemone sting and clown fish feeding imports crumbs that feed anemone Pollination mutualisms 23 24 Mutualisms Extrafloral nectaries on Acacia feed ants that protect the Acacia trees from herbivores and vines 25 26 Gut microbes allow termites and cows to digest cellulose Higher plants and fungi Mycorrhiza 27 Wood Wide Web 28 Coral bleaching loss of algae Zooxanthellae algae in corals 29 Fungi and algae lichens 30 Lichen mutualistic association of algae fixes energy and fungi protective cover Algal Niche Without fungal mutualist With fungal mutualist Light dry Moisture wet An alga participating in a symbiotic mutualism with a fungus As a lichen may have its realized niche expanded and shifted by the interaction 31 Symbiosis 2 species living together Rex Lowe Cyanobacterial endosymbionts live in diatoms that live on a macroalga Cladophora Nitrogen fixation cyanobacteria Rhizobium bacteria in legumes alders diatoms 32 3 species interactions Mutualists and cheaters Cleaner wrasses host fish cheater blennies N2 Milkweed bee cheater orchid Pollinator moth bumblebee nectar burglar Selection for refinement of cues and mimicry in co evolutionary race How much cheating can be tolerated before mutualism breaks down 33 34 Mutualism leaf cutter ants Atta spp culture fungi Culture of crops or livestock Mark Moffett photos 35 36 Herbivory fungivory leaf cutter ants Fungal garden in underground chamber of ant colony Minors defend workers from parasitic phorid flies Young queen carries bit of fungus to start new colony 37 38
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