Biol 302 Introduction1 COMMUNITY STRUCTURE 1.The Influence of COMPETITION 2.The Influence of PREDATION (HERBIVORY) Reading: General through cpt 23, and pp

Biol 302 Introduction2 COMMUNITY STRUCTURE 1.The Influence of COMPETITION 2.The Influence of PREDATION (HERBIVORY) Reading: General through cpt 23, and pp

Biol 302 Introduction3 1. Two species of Typha in Louisiana (Jim Grace’s work) 2. Reduce or remove number of Meadow Mouse ( Microtus ), and the population size of House Mouse ( Mus ) increases 3. Two species of Microtus, one in wetter parts, the other in drier parts of meadows. Remove one species from the wetter area, and the other species moves in THE INFLUENCE OF COMPETITION ON COMMUNITY STRUCTURE

Biol 302 Introduction4 Bullrush Cattail

Biol 302 Introduction5 1. Two species of Typha in Louisiana (Jim Grace’s work) 2. Reduce or remove number of Meadow Mouse ( Microtus ), and the population size of House Mouse ( Mus ) increases 3. Two species of Microtus, one in wetter parts, the other in drier parts of meadows. Remove one species from the wetter area, and the other species moves in THE INFLUENCE OF COMPETITION ON COMMUNITY STRUCTURE

Biol 302 Introduction6 Microtus (meadow mouse) Mus (house mouse)

Biol 302 Introduction7 1. Two species of Typha in Louisiana (Jim Grace’s work) 2. Reduce or remove number of Meadow Mouse ( Microtus ), and the population size of House Mouse ( Mus ) increases 3. Two species of Microtus, one in wetter parts, the other in drier parts of meadows. Remove one species from the wetter area, and the other species moves in THE INFLUENCE OF COMPETITION ON COMMUNITY STRUCTURE

Biol 302 Introduction8 4. Field bordered by trees and hedges: a. Lots of sparrows feeding on seeds on one part for the border b. Juncos feeding on seeds on other parts of the border c. Remove sparrows, and juncos spread and increased d. Sparrows allowed to return and juncos displaced 5.Connell (p94, 95, 137) [photo on 449] on Chthamalus and Balanus 6.The Ghost of Competition Past 7. Pianka’s lizards

Biol 302 Introduction9 Melospiza melodia (song sparrow) Junco hyemalis (d ark-eyed Junco)

Biol 302 Introduction10 4. Field bordered by trees and hedges: a. Lots of sparrows feeding on seeds on one part for the border b. Juncos feeding on seeds on other parts of the border c. Remove sparrows, and juncos spread and increased d. Sparrows allowed to return and juncos displaced 5.Connell (p94, 95, 137) [photo on 449] on Chthamalus and Balanus 6.The Ghost of Competition Past 7. Pianka’s lizards

Biol 302 Introduction11 Krebs Fig. 7.9; p94,95,137 Chthamalus Balanus

Biol 302 Introduction12 4. Field bordered by trees and hedges: a. Lots of sparrows feeding on seeds on one part for the border b. Juncos feeding on seeds on other parts of the border c. Remove sparrows, and juncos spread and increased d. Sparrows allowed to return and juncos displaced 5.Connell (p94, 95, 137) [photo on 449] on Chthamalus and Balanus 6.The Ghost of Competition Past 7. Pianka’s lizards

Biol 302 Introduction13 Frequency Environmental gradient

Biol 302 Introduction14 Frequency Environmental gradient

Biol 302 Introduction15 Frequency Environmental gradient GHOST OF COMPETITION PAST

Biol 302 Introduction16 The “Ghost of competition past”…. is a term coined by Joe Connell, to stress that inter specific competition acting as an evolutionary force in the past, has often left its mark on the behaviour, distribution or morphology of species, even when there is no present-day competition between them. Current competition…. is happening in the present

Biol 302 Introduction17 4. Field bordered by trees and hedges: a. Lots of sparrows feeding on seeds on one part for the border b. Juncos feeding on seeds on other parts of the border c. Remove sparrows, and juncos spread and increased d. Sparrows allowed to return and juncos displaced 5.Connell (p94, 95, 137) [photo on 449] on Chthamalus and Balanus 6.The Ghost of Competition Past 7. Pianka’s lizards

Biol 302 Introduction18 Three species of lizards eating prey of different sizes

Biol 302 Introduction19 Some Conclusions on the Effects of Competition on Community Structure 1. Interspecific competition is a plausible explanation for many aspects of community organization. 2. Current competition can easily be demonstrated. 3. As an alternative to current competition, the ghost of competition past can be invoked to account for present- day patterns - but it can be readily invoked because it is impossible to observe and difficult to prove!

Biol 302 Introduction20 4. The patterns uncovered, often support the competition hypothesis, but often have alternative explanations e.g. chance! Species may have evolved independently into specialists, and their specialized niches happen to be different; the species may never have competed. Some Conclusions on the Effects of Competition on Community Structure

Biol 302 Introduction21 1. KEYSTONE PREDATORS (Krebs ) a. removing rabbits from the English chalk grasslands 42 spp community to 3 spp in 7 years b. Removing Pisaster (starfish) from intertidal zones 15 spp community to 8 spp in 1 year (p 471) c. Sea otters off the coast of Alaska (p471,2) THE INFLUENCE OF PREDATION ON COMMUNITY STRUCTURE

Biol 302 Introduction22 A Keystone Species…. is a species (usually having a low frequency) in a community whose removal has strong effects on community diversity and composition; they are often top predators. Krebs p471, 621

Biol 302 Introduction23

Biol 302 Introduction24

Biol 302 Introduction25 Krebs p448?

Biol 302 Introduction26 Krebs Fig ; p472

Biol 302 Introduction27 Comparative status of nearshore communities in Rat Islands and Near Islands, western Aleutian Islands, Alaska Species Rat IslandsNear Islands Sea OttersAbundant Sparse Sea UrchinsRareDense LimpetsRareCommon ChitonsRareCommon MusselsRareCommon BarnaclesRareCommon MacroalgaeAbundant Rare Nearshore fishAbundantSparse Harbour sealAbundantSparse (from Simenstad et al Science 200:405)

Biol 302 Introduction28 Sea Otter Sea Urchin

Biol 302 Introduction29 Limpet Mussels Chiton Barnacles

Biol 302 Introduction30 Macro algae Harbour seal

Biol 302 Introduction31 Alternative [or Multiple] Stable States…. exist in a stable community if, when perturbed sufficiently, this stable community moves to a second equilibrium state, at which point it remains after the disturbance has been removed. For details see Krebs p508

Biol 302 Introduction32 2. INTERMEDIATE DISTURBANCE HYPOTHESIS (Krebs 452-3) a. Rabbits on sand dunes b. Coral reefs and Tropical rain Forests 3. INTERACTIONS INVOLVING PREDATION a. Chondrus, Enteromorpha, Littorina [snail], crabs and gulls (p453) b. Littorina has strong preference for Enteromorpha c. But typically don’t find many Littorina in Enteromorpha pools

Biol 302 Introduction33

Biol 302 Introduction34

Biol 302 Introduction35 2. INTERMEDIATE DISTURBANCE HYPOTHESIS: a. Rabbits on sand dunes b. Coral reefs and Tropical rain Forests 3. INTERACTIONS INVOLVING PREDATION a. Chondrus, Enteromorpha, Littorina [snail], crabs and gulls (p453) b. Littorina has strong preference for Enteromorpha c. But typically don’t find many Littorina in Enteromorpha pools

Biol 302 Introduction36

Biol 302 Introduction37 Periwinkle Littorina crabs & gulls

Biol 302 Introduction38 Enteromorpha

Biol 302 Introduction39 Gulls Crabs Periwinkle Enteromorpha Gulls Crabs Periwinkle Chondrus

Biol 302 Introduction40 1. Selective predation (e.g. Starfish on Mytilus ) are likely to enhance community diversity if their preferred prey are competitively dominant. 2. Even more generalist predators (e.g. Rabbits on grasses) may be expected to cause an increase in community diversity. 3. An intermediate intensity of predation is most likely to be associated with 'prey' diversity (e.g. rabbits on sand dunes), because too low an intensity may not prevent competitive exclusion of inferior prey species, and too high an intensity may drive preferred prey to extinction. Some Conclusions on the Effects of Predation on Community Structure

Biol 302 Introduction41 1. Selective predation (e.g. Starfish on Mytilus ) are likely to enhance community diversity if their preferred prey are competitively dominant. 2. Even more generalist predators (e.g. Rabbits on grasses) may be expected to cause an increase in community diversity. 3. An intermediate intensity of predation is most likely to be associated with 'prey' diversity (e.g. rabbits on sand dunes), because too low an intensity may not prevent competitive exclusion of inferior prey species, and too high an intensity may drive preferred prey to extinction. Some Conclusions on the Effects of Predation on Community Structure

Biol 302 Introduction42 1. Selective predation (e.g. Starfish on Mytilus ) are likely to enhance community diversity if their preferred prey are competitively dominant. 2. Even more generalist predators (e.g. Rabbits on grasses) may be expected to cause an increase in community diversity. 3. An intermediate intensity of predation is most likely to be associated with 'prey' diversity (e.g. rabbits on sand dunes), because too low an intensity may not prevent competitive exclusion of inferior prey species, and too high an intensity may drive preferred prey to extinction. Some Conclusions on the Effects of Predation on Community Structure

Biol 302 Introduction43 4. An intermediate level (frequency or intensity) of disturbance is also most likely to be associated with higher diversity communities (e.g. Tropical rain forests and coral reefs). 5. The role of predators in shaping community structure is likely to be least significant in communities where physical conditions are more severe or unpredictable. Some Conclusions on the Effects of Predation on Community Structure

Biol 302 Introduction44 4. An intermediate level (frequency or intensity) of disturbance is also most likely to be associated with higher diversity communities (e.g. Tropical rain forests and coral reefs). 5. The role of predators in shaping community structure is likely to be least significant in communities where physical conditions are more severe or unpredictable. Some Conclusions on the Effects of Predation on Community Structure

Biol 302 Introduction45 HARSH INTERMEDIATE BENIGN

Biol 302 Introduction46 ACACIA in Australia produces seed every year some establish in higher rainfall years insects destroy most seedlings ODD ONE GETS THROUGH need 3 successive wet years for success typically about every years i.e. Widely-spaced age classes

Biol 302 Introduction47 Acacia

Biol 302 Introduction48 LAMINARIA in sub-tidal deeper populations usually a single age class (low light) shallow populations usually multi-age i.e. in harsher conditions (low light) the ODD INDIVIDUAL survives in the unusual favorable year.

Biol 302 Introduction49 Laminaria

Biol 302 Introduction50 CHANCE COMPETITION PREDATION

Biol 302 Introduction51 Krebs Fig. 24.8; p495 A. CARNIVORESB. HERBIVORES C. PLANTS