L2 Competition chapter13 HO

Two-species interactions : 

Two-species interactions

Two-species interactions : 

Two-species interactions

Species competition : 

Species competition Ch.13 Molles 3rd ed, 2005 Ch.6 Townsend, Harper, Begon 2nd ed, 2003

Competition– key condition? : 

Competition– key condition? Share common resource Limit of resource

Modes of Competition : 

Modes of Competition Competing methods: Interference: Direct aggressive interaction between individuals. Exploitation (resource cmp): Rate of utilizing resource Competing subjects: Intraspecific: Competition with members of their own species. Interspecific: Competition between individuals of two species

Outlines : 

Outlines Resource limitation. Niche Mathematical and laboratory models Ecolg. and evolut. influences on niches. Coexistance Assemble rule

Chapter Concepts : 

Chapter Concepts I. Studies of Intraspecific competition provide evidence for resource limitation. A key role in slowing pop growth at high density Sigmoidal growth pattern Ex. Plant growth rate, Planthoppers growth

Resource Competition : 

Resource Competition Intraspecific Competition - Herbaceous Plants Plant growth rates and weights have been found to increase in low density populations. Competition for resources is more intense at higher population densities. leads to mortality among competing plants. Self-thinning

Intraspecific Competition Among Planthoppers : 

Intraspecific Competition Among Planthoppers Denno and Roderick, demonstrated intraspecific competition within populations of planthopper, Prokelesisia marginata (Homoptera ) Probably result of limited resources. ? body length, develp time, survivorship

Chapter Concepts : 

Chapter Concepts II. A niche reflects the environmental requirements of a species. History of niche concepts: Grinnell 1917, 24-- Physical environment Elton 1927-- Biological interactions Niche: summarizes environmental factors that influence growth, survival, and reproduction of a species. (current view)

Niches : 

Niches Hutchinson: defined niche as “a n-dimensional hyper-volume” n equates the number of environmental factors important to survival and reproduction of a species. Fundamental niche –no species interactions Realized niche: includes interactions such as competition that may restrict environments where a species may live.

Ex. Feeding Niches of Galapagos Finches : 

Ex. Feeding Niches of Galapagos Finches Grant found differences in beak size among ground finches translates directly into diet. Size (& hardness) of seeds eaten can measured by estimating by measuring beak depths. Effect of 1977 drought?

Ex. Feeding Niches of Galapagos Finches : 

Ex. Feeding Niches of Galapagos Finches Grant found differences in beak size among ground finches translates directly into diet. Size of seeds eaten can measured by estimating by measuring beak depths. Individuals with deepest beaks fed on hardest seeds. After 1977 drought, remaining seeds were very hard. thus mortality was most heavy in birds with smaller beaks. ? pop was dominated by larger birds at the end of the drought.

Chapter Concepts : 

Chapter Concepts III. Mathematical and laboratory models provide theoretical foundation for studying competitive interactions in nature. Metz summarized characters of models: Abstractions and simplifications of nature. Man-made construct; partly empirical and partly deductive. Used to provide insights into natural phenomena.

Mathematic model--Lotka-Volterra Model : 

Mathematic model--Lotka-Volterra Model Vito Volterra 1926, for explaining changes in the composition of a marine fish community in response to reduced fishing during WW I. Alfred Lotka 1932 independetly repeated Volterra’s analysis and extended it to pop density change during competition.

Mathematic model--Lotka-Volterra Modelfor 1 species : 

Mathematic model--Lotka-Volterra Modelfor 1 species Logistic model for population growth, r: the per capita rate of increase rm: intrinsic rates of increase m

L-V Model for two sp : 

L-V Model for two sp aß: effect between individual of each species. m m

Mathematical Model-- Lotka Volterra : 

Mathematical Model-- Lotka Volterra Effect of interspecific competition on pop. growth of each species: dN1 / dt = rm1N1 ((K1-N1-a12N2) / K1) dN2 / dt = rm2N2 ((K2-N2-a21N1) / K2) a12: effect of individual of species 2 on rate of pop. growth of species 1. a21: effect of individual of species 1 on rate of pop. growth of species 2.

Lotka-Volterra Model : 

Lotka-Volterra Model Predict pop growth for the two species will stop when: For sp 1: N1=k1-a12N2 ( k1, k1/a12 ) For sp 2: N2=k2-a21N1 ( k2/a21 , k2 ) or ( k2/b , k2 ) Zero Growth Isoclines Above: pop. Increasing Below: pop. Decreasing

When two species coexist, : 

When two species coexist, k1/a12 > k2 ? K1 > k2a12 k2/a21 > K1 ? K2 > K1 a21 ? 1 > a12 * a21

Lotka-Volterra Model : 

Lotka-Volterra Model In general, LV predicts coexistence of two species when interspecific competition is weaker than intraspecific competition.

Evidence for interspecific competition : 

Evidence for interspecific competition In the laboratory Ex. Paramecium Ex. Flour Beetle

Paramecia Lab Experiments : 

Paramecia Lab Experiments Gause, Paramecium caudatum, P. aurelia in two different concentrations of Bacillus pyocyaneus.

Slide 25: 

When grown alone, carrying capacity determined by intraspecific competition. When grown together, P caudatum quickly declined. Reduced resource supplies increased competition.

Competitive exclusion principle= Gause’s Principle : 

Competitive exclusion principle= Gause’s Principle An Russian ecologist, GF Gause Two species with identical niches cannot coexist indefinitely. One will be a better competitor and thus have higher fitness and eventually exclude the other.

Evidence for interspecific competition : 

Evidence for interspecific competition In the laboratory Ex. Paramecium Ex. Flour Beetle

Chapter Concepts : 

Chapter Concepts IV. Competition can have significant ecological and evolutionary influences on the niches of species. Evidence in the field Ex. Barnacle Ex. Small rodents Ex. Galapagos finches

Competition Examples : 

Competition Examples Barnacles: Balanus play a role in determining lower limit of Chthamalus within intertidal zone. (Connell) Did no account for all observed patterns.

The intertidal distribution of Chthamalus stellatus & Balanus balanoides : 

The intertidal distribution of Chthamalus stellatus & Balanus balanoides Competition evidence? Removal exp: remove B. ? C. could persisted Not remove, B. grew over and crushed the smaller C. individuals when they occurred in the same zone.? direct interference Why not exclude C. totally? B. appears unable to survive the desiccating conditions

Competition and Niches : 

Competition and Niches Competition can restrict species to their realized niches. But if competitive interactions are strong and pervasive enough, they may produce an evolutionary response in the competitor population. ? Changes fundamental niche.

Slide 33: 

IV. Competition can have significant ecological and evolutionary influences on the niches of species. Evidence in the field Ex. Barnacle Ex. Small rodents Ex. Galapagos finches

Slide 34: 

Brown studied competition among rodents in Chihuahuan Desert Kangaroo rat, Dipodomys spp, a large granivore b) A pocket mouse, Pergonathus sp. a small granivore

Competition Examples : 

Competition Examples Brown, rodents, Chihuahuan Desert. Predicted: if competition among rodents is mainly for food, then if remove larger granivorous rodents ? effect on small granivorous ones? ? effect on Insectivorous ones? Results supported hypothesis.

Slide 36: 

IV. Competition can have significant ecological and evolutionary influences on the niches of species. Evidence in the field Ex. Barnacle Ex. Small rodents Ex. Galapagos finches

Character Displacement : 

Character Displacement interspecific competition has been predicted to lead to directional selection for reduced niche overlap. Ex. Galapagos finches Geospiza fortis (medium ground finch), G. fuliginosa (small ground finch)

6 criteria for character displacement : 

6 criteria for character displacement M. Taper & T Case (1992) 1. diff bwt sympatric > allopatric populations 2. have a genetic basis 3. not due to original diff in founder pops 4. variations have effect on use of resource 5. competition demonstrated 6. not explained by resource availability (e.g. no diff of food availability on both sites)

* Coexistance Factors : 

* Coexistance Factors Ecological factors Variation in space & time (= Environmental heterogeneity ) Evolutionary factors Competition ghost Character displacement

Ecological Coexistance : 

Ecological Coexistance Environmental heterogeneity =spatial and temporal variation Ex. Mussels and sea palm (alga) Coast of Washington, gap formation

Coexistance factors-Evolutionary factors : 

Coexistance factors-Evolutionary factors Competition ghost Ex. Israeli rodents Character displacement Ex. Canadian sticklebacks (fish) Ex. Galapagos finches

Coexistance factors-Evolutionary factors : 

Coexistance factors-Evolutionary factors Competition ghost Ex. Israeli rodents (Meriones-blue, Gerbillus-pink) a niche differentiation of the realized niches, but also fundamental niches.

How significant is interspecific competition in practice? : 

How significant is interspecific competition in practice? The prevalence of current competition Surveys of published studies Effect on the assembling of a community? Assembly rule exists? through competition or mere by chance (= neutral models)

How widespread is intersp competitonin Nature? : 

How widespread is intersp competitonin Nature? 2 Surveys (1983), current competition Schoener, 164 studies, 390 sp, 150 exp 90% of studies, 57-76% of species show significant competition Connell, 72 studies, 215 sp, 527 exp Most studies, >50% species, 40% exp show significant competition large>small org., Marine > terrestrial

Critiques: : 

Critiques: Conclusion could be exaggerated Biased selection and reported studies too less exp on phytophagous insects More studies in temperate & mainland area

Is species in a community randomly assembled? (Neutral model) : 

Is species in a community randomly assembled? (Neutral model) Prediction: competing sp should be arranged regularly rather than randomly in niche space Test for Neutral model (null hypothesis): the data are rearranged into a form representing what the data would looks like in the absence of interspecific competition.

Slide 47: 

10 N Am. Lizard communities 4-9 species, 20 food categories Calculate mean resource overlap

Slide 48: 

Lowlor (1980): mean observed & expected resource overlap 100 randomly constructed comm., 4 reorganization Algorithms (RA): 1: retained the mim original comm structure, 4: retained the most of the orig comm struct Observed Expected Observed Expected

Summary : 

Summary Studies of Intraspecific competition provide evidence for resource limitation. A niche reflects the environmental requirements of a species. Mathematical and laboratory models provide theoretical foundation for studying competitive interactions in nature. Competition can have significant ecological and evolutionary influences on the niches of species. Ex. Character displacement, niche differentiation, competition ghost, free distribution..

E N D ! : 

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