Mutualism leaf cutter ants Atta spp culture fungi Ignacio Chapela ESPM Mark Moffett photos Herbivory fungivory leaf cutter ants Minors defend workers from parasitic phorid flies 1 Fungal garden in underground chamber of ant colony 2 Mutualisms Young queen carries bit of fungus to start new colony 3 4 Clown fish live in mutualistic symbiosis with sea anemone Extrafloral nectaries on Acacia feed ants that protect the Acacia trees from herbivores and vines 5 Clown fish mucus protects it from anemone sting and clown fish feeding imports crumbs that feed anemone 6 3 species interactions Mutualists and cheaters Cleaner wrasses host fish cheater blennies Milkweed bee cheater orchid Pollinator moth bumblebee nectar burglar 2 species Selection for refinement of cues and mimicry in co evolutionary race How much cheating can be tolerated before mutualism breaks down Taxon 7 Lump all Focus on particular species whose organisms into strong interactions limit 8 trophic levels important populations Interaction webs Community a group of species that co occur in food webs time and space food chains Food interaction webs depict feeding or other significant e g population limiting or regulating relationships among members of a community System group of entities united by interaction or interdependence to form or act as an entire unit Some of these interactions are strong others are weak How to simplify for study 9 Sometimes strong effects are mediated through food chains Hairston Slobodkin and Smith 1960 The world is green because predators hold herbivores in check assumes a 10 3 level food chain Fretwell Kansas world might have more or fewer than 3 trophic levels Trophic level functional grouping of organisms according to their primary food source Odd number of levels green plants resource limited bottom up limitation Levels 1 2 3 4 Odd numbers Green Even numbers Barren 11 Even number of levels barren plants consumer limited top down limitation Bottom up level number of energy transfers from fixation of organic carbon to reach level Top down level number of lower levels that are alternatively released and suppressed when this level is removed plus one Need to test which factor is limiting to understand food web controls on population abundance 12 Indirect interactions food webs food chains trophic cascades Why food chain theory shouldn t work 1 Green stuff could be inedible world is one trophic level 2 Consumers are co limited by predators and food or other factors 3 Omnivory blurs trophic levels My enemy s enemy is my friend x 4 Factors other than consumers or food limit populations 13 14 Species traits and interaction strength Not all species are created equal Pisaster R T Paine Focus on Keystone Species whose strong 15 interactions limit potentially Dominant populations 16 With Pisaster diverse intertidal Importance of top down forcing 17 without Pisaster mussel monoculture 18 LE 53 16 Number of species present Paine 1969 Keystone Species 20 Keystone species a species that consumes and limits the population of another species that would otherwise dominate the system Dominant species With Pisaster control 15 10 Without Pisaster experimental 5 0 1963 64 65 66 67 68 69 70 71 72 73 19 20 Sea Otter Pisaster Sea otter Keystones Distemper virus Corals mussels kelp grass trees Dominants Rhinovirus Keystone species have effects that are strong and stronger than would be expected from their abundances Power et al 1996 21 22 Urchins as strong interactors Strong interactors that trigger trophic cascades Sea otters Jim Estes et al Can graze and detach kelp boring through basal stipe exporting huge amounts Can forage down to 60 m Collectively urchins can wrestle kelp and weight it down Voracious eat 20 25 body weight per day Prey on sea urchins voracious grazers that can extirpate kelp Can persist subsist on uptake of dissolved organic matter or grazing microalgae so can persist without large kelp graze all new sporelings and maintain urchin barrens Kelp is a potential dominant structuring immediate subtidal and adjacent intertidal ecosystems 23 24 Kelp as strong interactor 2 vs 3 level food chains Aleutian Islands SE Alaska Prodigious growth rates and huge biomass Refuge for fin fish Wave break decreases erosion in intertidal causing sediment deposition Supplies intertidal with detritus and allows mudflats to be deposited Duggins 25 Otter state 3 trophic levels Urchin Barrens 2 trophic levels 26 Sea otters absent Sea otters present 27 28 Killer whale link Estes et al 1998 Campbell Fig 53 15 Evidence Estes and Palmisano 1974 Rat Island otters Complete cover of offshore kelp Rare urchins Lots of fin fish harbor seals bald eagles Near Island no otters Urchin barrens covered in mussels and barnacles Dense large mussels Few fish harbor seals or birds 29 27 years of monitoring the northeastern Atlantic revealed precipitous sea otter decline in 1990s throughout archipelago off western Alaska down to 10 of 1980s populations Hypotheses Toxins PCBs Disease Starvation Climate stress Predation 1st killer whale attack on otter observed in 1991 Computed probability that if rate of whale predation constant over 27 y of census probability of not observed before 1990 0 006 Ecosystem responses urchins increasing 8x and kelp decreasing 10x over 12 y where otters missing Clam Lagoon otter refuge too shallow for whales to enter otters still present no other food web or ecosystem changes urchins rare and small kelp communities in tact 30 Human fishing whaling killer whales Biomass tones X 10 of tons Biomass millions Great whales birds 6 otters sea lions urchins fish Cetaceans Whales Pinnipeds Seals 3 2 1 kelp Estes Springer hypothesis for Northern Pacific food web 31 killer whales Human industrial fishing whaling Biomass estimates for great whales blue and seals red before and after their recent declines in the Aleutian Islands and Bering Sea region Springer et al 2003 Historical Current 32 Geography of reported whale harvests all species in the North Pacific Ocean and Bering Sea from 1946 through 1976 Springer et al 2003 Great whales birds otters sea lions urchins fish kelp Estes Springer hypothesis for Northern Pacific food web 33 34 Springer et al PNAS 2003 Marine megafaunal collapse in N Pacific Great Whales Harbor Seals Steller Sea Lions Sea Otters 1 0 0 8 0 6 0 4 Proportion of maximum 0 2 0 0 1950 1960 1970 1980 1990 2000 Year Figure 2 The sequential collapse of marine mammals in the North Pacific Ocean and southern
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