Coevolution of competitors

Transcription

1 Coevolution of competitors 1) Coevolution 2) Ecological character displacement 3) Examples 4) Criteria for character displacement 5) Experiments on selection and evolution 6) Convergent character displacement 7) Community-wide character displacement 8) Divergence via apparent competition

2 1) Coevolution Strict definition: Reciprocal evolutionary change of interacting species. In this course we will consider coevolution and other evolutionary consequences of Ÿ Competitive interactions Ÿ Predator-prey interactions Ÿ Host-parasite interactions Ÿ Mutualistic interactions

3 2) Ecological character displacement The process whereby one species influences the evolution of another via interspecific competition. Similar to coevolution of competitors, but also includes cases of non-reciprocal evolution (one species affects a second, but not vice-versa.

4 2) Ecological character displacement The term is usually applied in the case of resource exploitation competition, not interference competition Consumers Resource

5 Prediction of (simple) theory for evolution in a single species Only intra-specific competition is present Carrying capacity curve (K) 2) Ecological character displacement Position on resource gradient that maximizes population size resource gradient Mean of resource utilization curve should evolve to the point at which population size is maximized.

6 2) Ecological character displacement Prediction of (simple) theory for evolution of two competing species Both inter- and intra-specific competition are present Carrying capacity curve (K) species 1 species 2 utilization curves resource gradient

7 Assumptions: 2) Ecological character displacement - Competition is symmetric - No other sources of selection on resource utilization - Carrying capacity has a simple shape Additional predictions: - Divergence does not occur if resource utilization curves are very broad compared to K-curve - Divergence occurs most rapidly when there is an initial difference in utilization between the species.

8 3) Examples Isopods in separate rivers each evolve to exploit the most abundant fungi This pattern breaks down when both species occur together Water%20slater.htm Isopod survival on single-fungus diet Proasellus coxalis Asellus aquaticus Rossi et al. (1983) Evolution Abundance of fungus species in wild

9 3) Examples Character displacement in Eurasian nuthatches? Bill length (mm) Sitta tephronota Sitta neumayer Grant (1986) Evol Biol

10 3) Examples Bill length (mm) Sitta tephronota Maybe character displacement would be a more convincing interpretation if the pattern had this form instead Sitta neumayer Grant (1986) Evol Biol

11 3) Examples Niche differentiation in plant communities 2002 Jena Experiment established Mixture plots 2010 Plant material collected 2010/11 Cuttings and seedlings propagated 2010/11 Test communities established Field monocultures and mixed plots were established in 2002 in Jena, Germany. After 8 years, plants were collected and assembled in test monocultures and mixtures in the greenhouse. Monoculture plots Zuppinger-Dingley et al. (2014) Nature

12 3) Examples Species grown for 8 years in mixtures (Mix) had greater differences in plant height, specific leaf are (SLA) and functional diversity (calculated from height, SLA, and reproductive biomass) than species grown in monocultures (Mono). Means + SE are averages over 50 species combinations. Genetic basis is not known Height difference 0.6 SLA difference 0.4 Functional diversity Mono Mix Mono Mix Mono Mi x Zuppinger-Dingley et al. (2014) Nature Selection history

13 2.0 3) Examples Biodiversity effects (g per pot) Biodiversity effects Net effects Complementarity effects Sampling effects Biodiversity effects (the biomass increase resulting from growing plants in mixtures than monocultures) were stronger in plants that had been grown in mixtures for 8 years than plants raised in monocultures. The genetic basis of these effects is not known. 0 Mono Mix Selection history Zuppinger-Dingley et al. (2014) Nature

14 3) Examples Character displacement in stickleback Solitary Pair Gill raker length (size-adjusted) Schluter & McPhail (1992) Am Nat photo: T Hatfield

15 50 Priest, Balkwell, Emily Lakes 3) Examples Pairs occurred in 5 small-lake systems Paxton Lake Little Quarry Lake Hadley Lake Enos Lake 49 Vancouver Island Schluter & McPhail (1992) Am Nat

16 4) Criteria for demonstrating character displacement 1. Chance should be ruled out as an explanation (i.e., replication needed) 2. Phenotypic differences between populations should have a genetic basis 3. Enhanced differences in sympatry should be the outcome of evolutionary shifts, not simply biased extinction of similar forms 4. Morphological differences should reflect differences in resource use 5. Sites of sympatry and allopatry should not differ in food, climate, etc. 6. Independent evidence should be gained that similar phenotypes compete for resources. Schluter & McPhail (1992) Am Nat

17 4) Criteria for demonstrating character displacement Evidence on multiple origins from complete genome sequences (chrxv) Paxton benthic Solitary Priest benthic Paxton limnetic Priest limnetic Solitary Solitary Solitary Pacific marine Enos limnetic Enos benthic Solitary Little Quarry limnetic Little Quarry benthic Solitary Solitary Atlantic marine

18 4) Criteria for demonstrating character displacement Experimental test of declining competition during divergence Character displacement sequence First marine invasion Experimental ponds Intermediate form evolves Time Second marine invasion Character displacement Modern species pair benthivore zooplanktivore Experimental treatments Early in series ( pre-displacement ) Late in series ( post-displacement ) benthivore Phenotype zooplanktivore Pritchard & Schluter (2001) Evol Ecol Res

19 4) Criteria for demonstrating character displacement Experimental test of declining competition during divergence Character displacement sequence Time First marine invasion Intermediate form evolves Second marine invasion Character displacement Modern species pair Experimental treatments benthivore zooplanktivore Growth rate (length in mm) Pond 1 Pond 2 Pond 3 Early in series ( pre-displacement ) 26.5 Late in series ( post-displacement ) benthivore Phenotype zooplanktivore 26.0 Early in series ( pre-displacement ) Treatment Late in series ( post-displacement ) Pritchard & Schluter (2001) Evol Ecol Res

20 5) Experiments on selection and evolution Selection in an experimental intermediate population 4.0 Ln growth rate Growth of intermediate phenotypes in ponds in the presence and absence of a limnetic competitor benthic-like Morphological index limnetic-like Schluter (1994) Science

21 5) Experiments on selection and evolution Experimental sympatry between Anolis lizard species on three islands Shift in perch height by A. carolinensis (a native species) after experimental introduction of A. sagrei (an invasive species) in 1995 to small, medium, and large islands in Florida. A. carolinensis by J.Losos Stuart et al (2014) Science A. sagrei by T. Sanger

22 l l 5) Experiments on selection and evolution Mean number of toepad lammellae in 2010 on these same islands plus a few other islands colonized about the same time l l l 24.5 A. carolinensis by J.Losos A. carolinensis island mean toepad lamellae number l l ll l Toe pad lamellae are adhesive, setae-laden scales. Larger and better developed toepads improve clinging ability, allowing lizards to better grasp narrow perches absent A. sagrei presence present Stuart et al (2014) Science

23 6) Convergent character displacement When species converge as a consequence of interspecific competition. Not to be confused with a failure to diverge despite interspecific competition. Theory by Abrams (1987) predicts circumstances that might favor convergence, such as nonsubstitutable resources. Interspecific competition for the same, limiting non-substitutable resource (e.g., light) might cause species to evolve similar traits to harvest it (e.g., both of two plant species redirect growth toward shoots). There are no examples.

24 7) Community-wide character displacement vertical lines represent means horizontal bars represent + standard deviation horizontal lines represent ranges Dayan et al. (1989) Ecology courses/5/content/ htm

25 8) Divergence via apparent competition Apparent competition Predator Consumers

26 8) Divergence via apparent competition Character displacement in Passiflora leaf shape via apparent competition? Heliconius cydno (host generalist) Gilbert (1975) In Coevolution of animals and plants (ed. L. E. Gilbert and P. H. Raven), pp Costa_Rica/Elaimet_Tortuguero/