Ecology Lecture Notes 10 Competition and Niches - PDF

Ecology Week 10 Lecture 17 – Competition and the Ecological Niche  Ecological niche Abiotic and Fundamental Niche resources Realized Niche Biotic Geographic Range Dispe...

Ecology Week 10 Lecture 17 – Competition and the Ecological Niche  Ecological niche Abiotic and Fundamental Niche resources Realized Niche Biotic Geographic Range Dispersal Ability  Ecological niche Realized Niche: the range of abiotic and biotic conditions a species can tolerate and the ways of life it pursues Often conceived as a multidimensional space Niche Axes: Water depth Prey Size Niche Axes: Water depth Prey Size Salinity Predator density Nesting sites Hiding sites Activity patterns (diurnal?) Temperature Etc  Ecological niche Realized Niche: the range of abiotic and biotic conditions a species can tolerate and the ways of life it pursues Often conceived as a multidimensional space Can be subdivided into components: “feeding niche”, “roosting niche”, etc Five species distributed across niche space: How to increase diversity? C C Fish Diversity 10 Morphology as proxy for niche 11  Adaptive Radiation Adaptive radiation: Recent, rapid diversification of a clade in response to the opening of new niche space African Cichlids  Darwin’s Finches Finch-like ancestor 13  Hawaiian Honeycreepers Canary-like ancestor 14  Niches & Competition Competition - Use or defense of a resource by one individual that reduces that resource for others 15  Competition Use or defense of a resource by one individual that reduces that resource for others – Can be intraspecific or interspecific Interference competition – Direct interaction (e.g. physical aggression, territorial fights) Exploitative competition – Depleting shared resources (e.g. bats, hummingbirds, and nectar) 16  Resources Resource: Substance or factor required by an organism for normal growth, maintenance, and reproduction – Can be depleted – Decreased resources decrease population size What does this include? Different for animals/plants? 17  Resources Plants: Animals: – Nutrients – Food – Access to sunlight – Roosting space (bats) – Pollinators/seed – Nesting sites (birds) dispersors – Water – Water – Mineral licks – Space Not resources: Temperature, water salinity, water depth, activity patterns 18 Space as a resource: barnacles on rocky coast 19 Gause’s competition experiments (1934, 1935) Later repeated with flies, mice, beetles, plants: in 30-70 generations one dies out 20  Competitive exclusion principle Two species cannot live together indefinitely on same limiting resource. Which means? – Limiting resource = the factor that, when increased, increases population size “Complete competitors cannot coexist” Hardin (1960). 21  Different Niches allow Coexistence Competition among Diatoms Asterionella requires more silica relative to phosphorous than Cyclotella (although both require both) 22  Different Niches allow Coexistence Barnacle coexistence - Balanus pry Chthamalus off rocks - When Balanus removed, Chthamalus moves down 23  Competition and resource use Resource partitioning: when co- occurring species use different resources 24 Fish size eaten by co-occuring seabirds 25 Resource partitioning in warblers 26  What processes can bring about a pattern of resource partitioning? 27  What processes can bring about a pattern of resource partitioning? – Species sorting – process that determines community composition based on whether a given species can invade, given local biotic and abiotic conditions – Character displacement – process by which co- occurring species evolve differences to reduce competition 28 Character Displacement  Character Displacement Geospiza Geospiza fuliginosa fortis Galapagos Finches  Character Displacement Geospiza Geospiza fuliginosa fortis Galapagos Finches Character Displacement: A Case Study with Bats & Flowers  Competition for Pollination Sp. A Sp. A  Competition for Pollination Sp. A Sp. A  Competition for Pollination Sp. A Sp. A Sp. B Sp. B  Interspecific Pollen Transfer Sp. A Sp. A Sp. B Sp. B  Interspecific Pollen Transfer Pollen received 80 grains Sp. A 20 grains Sp. A Sp. B Sp. B  Interspecific Pollen Transfer Pollen dispersed 80 grains 20 grains Sp. A Sp. A Sp. B Sp. B Burmeistera (Campanulaceae) Site of Pollen Placement Hypothesis: Differences in exsertion evolve to reduce competition Levels of Resource Partitioning Mechanism: Individuals compete for resources Process: Populations diverge in phenotype Pattern: Communities show trait overdispersion Levels of Resource Partitioning Mechanism: Individuals compete for resources Process: Populations diverge in phenotype Pattern: Communities show trait overdispersion  Competitive Mechanism Does divergence in exsertion length reduce pollen transfer between species? Pollen Transfer Experiments  Experiments Bellavista Yanayacu 1) sodi-cyli 2) sodi-succ 3) sodi-borj 4) sodi-cera Diff = 5.9 Diff = 9.0 Diff = 8.0 Diff = 0.5  Experiment 1) sodi-cyli Diff=5.9 250 t (8)=3.36 t (8)=-3.35 p=0.010 p=0.010 200 Pollen Grains Transferred 150 sodi pollen 100 cyli pollen 50 0 sodi sodi cyli cyli Female Flower  Experiment 2) sodi-succ Diff=9.0 250 t (8)=8.94 t (8)=-4.51 p