SPECIES INTERACTION AND COMMUNITY STRUCTURE BONAVITACOLA, DOLOROSO, QUEVEDO, VALLEJOS
WHO EATS WHO? Feeding relationships Most documented species interaction
FOOD WEB Community portrait based on feeding relationships Summary of feeding relationships
COMMUNITY FOODWEBS
CHARLES ELTON Simplified studies to derive foodwebs Complexity of feeding interactions
KIRK WINEMILLER (1990) Feeding relations among fish Studied these interactions in Venezuela and Costa Rica
STUDY ON CAÑO VOLCÁN Caño Volcán is a medium-sized stream Supports 20 fish species Study focused on the complexity of interactions and trophic levels to determine biologically significant relationships.
Complex relationships even with a small number of organisms
Remove weak feeding relationships to make it a bit more comprehensible
ROBERT PAINE (1980) Species feeding activity Strong interactions Influential trophic relations in which the feeding activity of a few species have a dominant influence on community structure Defined not only by the quantity of energy flow but also by the degree of influence on the community structure
TEJA TSCHARNTKE Study on the wetland reed, Phragmites australis
DOMINANT/FOUNDATION SPECIES Species that have substantial influences on community structure as a consequence of their high biomass
Interactions were studied in the Elbe river in Hamburg Identification of interactions (strong and weak) Well represented foodweb
KEYSTONE SPECIES
KEYSTONE HYPOTHESIS The feeding activities of a few keystone species may control the structure of communities
Robert Paine Reasoning behind the Keystone hypothesis prey populations under the carrying capacity low potential for competitive exclusion increase the species that coexist in a community due to low potentials of competitive exclusion
FOODWEB AND DIVERSITY Paine s Zooplankton Increase in the number of species = increase in the species that are predaceous Atlantic ocean 81 species,16% are predators Sargasso sea 268 species, 39% are predators
INTERTIDAL ZONE STUDY Mukkaw Bay, Washington
13 Species Diversity
SUBTROPICAL STUDY Northern gulf of California
45 Species Diversity
Conclusion Mukkaw in comparison to Northern Gulf From 13 species to 45 species In terms of predators 2 species to 11 species Predation hypothesis
PAINE S 1 ST EXPERIMENT Removed the top predator in the food web at Mukkaw Bay and then repeated it in New Zealand Study sites were located in intertidal zones Lasted for 2 years
EXPERIMENTAL REMOVAL OF SEA STARS
EXPERIMENT DESIGN Pisaster Control Setup Experimental Setup
RESULTS The control setup showed a constant number of species (15) The experimental setup showed a decrease of species from 15 to 8. Shows that Pisaster is a keystone species since its removal caused a collapse in the community
EXPERIMENT IN NEW ZEALAND Similar to what was done in Mukkaw Bay The difference is that the top predator was another species of sea star, Srichaster australis, which also feed on mussels, barnacles, and other invertebrates. 9 months
RESULTS The control setup showed a constant number of species (15) The experimental setup showed a decrease of species from 20 to 14 in just 9 months
RESULTS The disappearance of species was mainly from competitive exclusion Competition of space since the coverage of mussels grew in the absence of a predator leaving no room for other species
SNAIL EFFECTS ON ALGAL DIVERSITY Experiment by Jane Lubchenko (1978) Studies how herbivorous intertidal snails influence the diversity of intertidal algae. Studied feeding preferences of Littorina in the laboratory
HERBIVORES (1) Increase plant diversity (2) Decrease plant diversity (3) Both
1 ST EXPERIMENT Indicate that algae fell into low, medium, or high preferences
Green Algae (Enteromorpha spp.) Small Ephemeral Tender Red Algae (Chondrus chrispus) Tough Perennial
Generally, the snails would highly prefer green algae.
They would only eat the red algae if there was no other choice
2 ND EXPERIMENT Studied the abundance of algae and Littorina in tide pools Tide Pool
Tide pools with high density of green algae had low densities of snails
Tide pools with high density of snails were dominated with red algae
2 ND EXPERIMENT In the absence of Littorina (snails), Enteromorpha (green algae) competitively displaces Chondrus (red algae)
Control Pool Without manipulation of snails, the abundance of the algae remained relatively constant
Addition of snails in a tide pool Reduced the Enteromorpha (green algae) cover
Reduction of snails in a tide pool Increased the Enteromorpha (green algae) cover
WHAT CONTROLLED THE SNAILS POPULATION??
WHAT CONTROLLED THE SNAILS POPULATION? Green Crab (Carcinus Maenus) Live in the canopy of green algae and feeds on juvenile snails
WHAT CONTROLLED THE CRABS POPULATION? Seagulls Shows how complex a local food web is
Low to Medium Density = Increase in the abundance of algal species Low density = feeding activity of snails is not sufficient to prevent green algae from dominating
Medium Density = Snail s feeding prevents competitive exclusion and increases algal diversity
Medium to High Density = Decrease in the abundance of algal species
High Density = Feeding requirements of snails are so high they eat their preferred algae as well as less preferred species
EMERGENT HABITATS Rock surfaces that are not submerged in tide pools during low tide Dominant algal species in this area are from genera Fucus and Ascophyllum, species not preferred by snails. Emergent Habitat
Algae diversity was high when the density of snails was low. Snails feed only on the tender algae such as Enteromorpha, ignoring Fucus and Ascophyllum
DIFFERENCE OF DOMINANT & KEYSTONE SPECIES Dominant species species with a significant effect on the community as a consequence of their high biomass Keystone species regardless of biomass, species that exert strong effects on their community structure
EXOTIC PREDATORS
Exotic Predators can Simplify or collapse the structure of food webs!
INTRODUCED FISH Lake Victoria Located in East Africa Used to house over 400 different Fish species Harbors one of the greatest concentrations of fish species in the world The greatest devastation ever wrought by an introduced Predator
WHAT HAPPENED TO LAKE VICTORIA? The Nile Perch (Lates nilotica) happened! This predacious fish caused the greatest extinction of vertebrate animals in modern times From 400 different species, only three remain to dominate the lake. Omena (Rastrineobola argentea) is the only native species to survive Hundreds of fish species appear to be going extinct because of the introduction of only ONE fish species in an ecosystem with 400 different fish species.
DIRECT INFLUENCE V.S. INDIRECT INFLUENCE An exotic species can directly influence a population via predation. The simple eating of the population by the introduced species They may also affect a population indirectly The new species may have the same food source as a certain population They may change certain environmental conditions such as temperature or ph level rendering other species unable to survive
Example
Introduced Species*
Direct effect on population Pacman Introduced Species*
Indirect Effect on population Pacman Introduced Species*
Introduced species can produce changes in ecosystems that may in turn strongly influence populations and communities.
PHILIPPINE CONTEXT Knife Fish Ornamental fish Originally from Thailand, Vietnam, India, and Malaysia Released into Laguna Lake during Ondoy Feeds on fishes naturally found in the lake causing a decrease in the abundance of other fishes
MUTUALISTIC KEYSTONES Mutualists = Act as Keystone Species Keystone Species the species must have relatively LOW biomass and HIGH IMPACT on community structure
KEYSTONE SPECIES: CLEANER FISH Cleaner Fish and its clients = clean other fish of ectoparasites Labroides dimidiatus, cleaner wrasse - Remove and eat 1200 parasites a day (Grutter 1999) - 4x the number of parasitic isopods in reefs without cleaner wrasse
KEYSTONE SPECIES: CLEANER FISH Affects diversity of fish in coral reefs 400m area, with 2-6m depth 29 natural disappearances/appe arances of cleaner wrasses Change of 24% in fish species richness
KEYSTONE SPECIES: ANTS South African Ants = disperse 30% of seeds Mutualism: Ants get food = elaiosomes Bury seeds far away from fire and seed-eating rodents Fynbos = shrubland/heathland vegetation area in South Africa
KEYSTONE SPECIES: ANTS Linepithema humile, Argentine Ant Invasive, do not disperse seeds Native species most impacted are the ones most likely to disperse larger seeds
OTHER MUTUALISTS Pollinators Mycorrhizal Fungi