BIOL 4120: Principles of Ecology Lecture 12: Interspecfic competition Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

Outline (chapter 13) 13.1 Interspcific competition 13.2 Lotka-Volterra model 13.3 Laboratory experiments support L-V model 13.4 Competitive exclusion principle 13.5 Competition is influenced by nonresource factos 13.6 Temporal variation in environmental factors 13.7 Multiple resources 13.8 Competition change along environmental gradients 13.9 Niches of species 13.10 Resource partitioning 13.11 Competition influence national selection 13.12 Competition involves biotic and abiotic factors Lecture 12: Chapter 13:

13.1 Interspecific competition A relationship in which the populations of two or more species are affected adversely (--) Seek a common resource in short supply Food; Living space; etc An example: squirrels, mice, deer, various birds competing for acorns Model One. Two forms Exploitation Interference Model Two. Six forms Consumption preemption Overgrowth Chemical interaction Territorial encounter

Consumption Preemption Overgrowth Chemical interaction Territorial Utilization of a shared resource by 2 species Preemption Occupation of a site by 1st organism stops occupation by 2nd organism Usually sessile organisms Overgrowth Where organism covers another preventing access to a resource. Trees shade other plants Chemical interaction Release of toxin to inhibit or kill competing organisms Allelopathy in plants Territorial Behavioral exclusion of 1st organism by 2nd organism defending territory Encounter Non-territorial encounters cause a negative effect on one or both species Lion and wild dogs over a antelope kill

12.2 Possible outcomes of Interspecific competition When two species compete, how many outcomes? Species 1 wins, species 2 loses Species 1 loses, species 2 wins Coexistence (stable equilibrium) Competition can go wither way (unstable equilibrium) These competition results can be described by Lotka-Volterra model.

Lokta-Volterra Model Derived from logistic equation Add influence of another species (a competition component) alpha(2,1)=alpha Alpha(1,2)=beta

Lokta-Volterra Model αN2 and βN1: effect of interspecific competition, namely, where α and β per capita effects of competition In term of resource use, an individual of species 2 is equal to α individuals of species 1 No interspecific competition, then α and β are 0 and normal growth to carrying capacity Interspecific competition is density dependent Need to explain dN/dt=0, then N1=K1-alpha N2 dN2/dt=0, then N2=K2-beta N1 These two are the zero growth isoclines

(a) Species 1 alone or no competition Diagonal line is zero growth isocline

(b) Species 2 alone or no competition

(c) Species 1 inhibits growth of species 2 and latter goes extinct

(d) Species 2 inhibits growth of species 1 and latter goes extinct

(e) Unstable situation, both inhibit in a density dependent manner (e) Unstable situation, both inhibit in a density dependent manner. Depending on initial density, either can make other extinct

4/23/2017 (f) Each species inhibits its own population growth more than competitor. Neither can eliminate competitor

4/23/2017 How to remember which wins? Easy: large K wins, (c) K1 larer, species 1 wins, (d), K2 large, species 2 win, (e) one side sp1 wins, one side sp2 wins, (f) nobody wins, co-exist

13.3 Laboratory experiments support the Lotka-Volterra Equations Russian biologist G.F. Gause Competition between two species P. aurelia has a high growth rate and can tolerate a higher population density Two Paramecium (unicellular ciliated protozoan) One with higher rate of growth: Extinction of slower grower With different food supplies: Coexistence

Diatom experiment David Tilman, University of Minnesota Asterinella formosa (Af) and Synedra ulna(Su) compete for silica for the formation of cell walls. Adequate silica, coexist Insufficient silica, Su drove Af to extinction

13. 4 Competitive exclusion principle Complete competitors can not coexist. One species must go extinct Complete competitions: two species that live in the same place and possess exactly the same ecological requirements. Assumptions: Exactly the same resource requirement (no more, no less) Environmental conditions remain constant Most of the time species can coexist

13.5 Competition is influenced by non-resource factors Many non-resource factors would influence the outcomes of the competition. For example, space, light. Favor species with high photosynthetic rate, allocate C to height growth and leaves production (fast-grow species)

Patterns of seed germination along T gradient Fakhri Bazzaz, Harvard University (Retired) Five annual species T influences the germination, thus seedling establishment, resource competition and structure of community.

13.6 Temporal variation in environment influences competition interactions As environmental conditions vary, the competition advantages change No one species can reach sufficient density to displace its competitors; Thus lead to co-exist. Shift in dominant grass species caused by moisture

13.7 Competition occurs for multiple resources Systems are not simple one resource situations Usually competition for more than one resource Territorial defense against wide range of other species Plants Monoculture Root competition Skeleton weed reduce by 35% Shoot competition Skeleton weed reduced by 53% Root and shoot competition Skeleton weed reduced by 69% Thus clover superior to skeleton weed for all resources

13.8 Relative competition abilities change along environmental gradients Effect of interspecific competition across an environmental gradient Note changes in response when in mixture

Similar effect for summer annuals and moisture gradient Also happens in nature with water, anoxia and salt stress in a salt marsh

Chipmunks Alpine Lodgepole Yellow Pine Least Cold tolerant Most aggressive Needs shade Yellow Pine aggressive Least Heat tolerant Least chipmunk can occupy from sagebrush to alpine zone. If yellow pine is removed, least chipchunk will move up. If least chipchunk is removed, yellow pine chipmunk will not move down. Lodgpole pine chipmunk is restricted to shade area, is vulnerable to heat. Lodgepole is the most aggressive, may limit the downslope range of alpine chipmunk.

13.9 Niche of a species Concepts of niche describes how an organism or population responds to the distribution of resources and competitors (e. g., by growing when resources are abundant, and predators, parasites and pathogens are scarce) and how it in turn alters those same factors. dimensions of a niche: represent different biotic and abiotic variables. These factors may include descriptions of the organism's life history, habitat, trophic position (place in the food chain), and geographic range. According to the competitive exclusion principle, no two species can occupy the same niche in the same environment for a long time.

Concepts of niche Fundamental niche: range of conditions and resources a species can use to survive and reproduce under no interference by other species Realized niche: portion of fundamental niches that a species actually exploits as a result of interactions with other species (e.g., competition).

Examples Distribution of twp species of cattail (Typha latifolia and T. angustifolia) Fundamental Niche: Tl: water depth: -20~ 70 cm Ta: -20~110 cm Realized Niche: Tl: -20 ~ 70 cm Ta: 20 ~ 110 cm (Changes) Niche overlap: 20-70 cm

Fundamental and realized niches

Competition release A species expands its niche in response to the removal of a competitor Two examples Response of Stipa neomexicana plants Commercial whaling in Antarctic Ocean

Response of Stipa neomexicana plants Jessica Gurevitch University of New York at Stony Brook Stipa: C3 perennial grass Semi-arid grassland in Arizona

Commercial whaling in Antarctic Ocean Baleen whales: 1 million a century ago eat Antarctic krill (4% of body weight) Now, less than 200,000 Other krill-dependent predators such as seals and penguins have been found greatly increased in abundance Competition release due to the dramatic decrease in baleen whale population

13.10 Resource partitioning “Complete competitors can not co-exist” Why did not the best competitor force others out? Co-existing species must be different in the use of resources Niche differentiation: differences in the range of resources used or environmental tolerance Examples: Plants grow together Animals share the same habitat

Resource partitioning Use water and nutrients at different depths Spatial differentiation.

Resource partitioning Size (diameter) of canine teeth for small cat that co-occur in Israel. Size is correlated with size of prey selected by different species. Morphological differentiation.

Another example Seven Anolis lizards in tropical rainforest Share common food needs — mainly insects. They avoid competition by occupying different sections of the rainforest the leaf litter floor shady branches All resources are subject to partitioning, such as space, food, nesting sites. This minimizes competition between similar species. (Temporal differentiation.)

Niche dimensions Rarely do two or more species possess exactly the same combination of requirement. Species may overlap on one D of the niche, but not on another.

13.11 Competition can influence natural selection Competition is at the heart of Darwin’s theory of natural selection. Characteristics that enable an organisms to reduce competition will function to increase fitness. Character displacement

Character displacement The outcome of the competition was a shift in feeding niches. When the shift involves features of the species’ morphology, behavior, or physiology The process of evolution toward niche divergence in the face of competition

13.12 Competition involves both biotic and abiotic factors Removal experiment is an effective method to study competition Hidden treatment effects: removal changes space, light, soil temperature, and moisture, evaporation. Competition is a complex interaction involving a variety of environmental factors that directly influence survival, growth, and reproduction. Outcome of competition may differ markedly under different set of environmental conditions. Finally, we need to understand that

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FACILITIES MANAGEMENT DEPARTMENT DEPARTMENTAL NOTIFICATION LOCATION CAMPUS-WIDE   PROJECT IN RESPONSE TO THE DROUGHT AND HEAT THIS SUMMER, ALL TREES THAT HAVE EXCEEDED THEIR PERMANENT WILTING POINTS WILL BE REMOVED DURATION   TWO DAYS, OCTOBER 15-16, 2007 (FALL BREAK)

Science 12 October 2007: Vol. 318. no. 5848, pp. 268 – 271 Reports Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate Natalia N. Pouchkina-Stantcheva, et al. Theory suggests it should be difficult for asexual organisms to adapt to a changing environment because genetic diversity can only arise from mutations accumulating within direct antecedents and not through sexual exchange.

Science Reports (cont.) Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate Natalia N. Pouchkina-Stantcheva, et al. In an asexual microinvertebrate, the bdelloid rotifer, we have observed a mechanism by which such organisms could acquire the diversity needed for adaptation. Gene copies most likely representing former alleles have diverged in function so that the proteins they encode play complementary roles in survival of dry conditions.

Science Reports (cont.) Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate Natalia N. Pouchkina-Stantcheva, et al. One protein prevents desiccation-sensitive enzymes from aggregating during drying, whereas its counterpart does not have this activity, but is able to associate with phospholipid bilayers and is potentially involved in maintenance of membrane integrity. The functional divergence of former alleles observed here suggests that adoption of asexual reproduction could itself be an evolutionary mechanism for the generation of diversity.

Al Gore, UN panel share Nobel for Peace U.N.'s IPCC (Intergovernmental Panel on Climate Change) For Global warming