interspecific competition

1. Interspecific Competition

3. Observational negative correlations between species attributed to present competition or past (�ghost of competition past�) can�t determine cause and effect other factors may be involved

4. Observational + Comparison to null model compare observed patterns to those generated by chance alone statistical comparison challenge is to formulate the appropriate null model

5. Experimental addition/removal studies manipulate presence and/or density of would-be competitors must account for density effects provides strong inference (strong evidence for or against) cannot be done with many species

6. 6 Mechanisms of Competition(after Schoener 1983) 1) Consumptive � one species competes with another by consuming a shared resource

7. 6 Mechanisms of Competition 2) Preemptive � occupation of physical habitat by one species, thereby excluding another

9. 6 Mechanisms of Competition 3) Overgrowth � one species grows over another

10. 6 Mechanisms of Competition 4) Chemical � �chemical warfare� allelopathy in plants; has not been convincingly demonstrated growth inhibitors in animals

11. 6 Mechanisms of Competition 5) Territorial � aggressive behavioral exclusion

12. 6 Mechanisms of Competition 6) Encounter � nonterritorial encounters between foraging species wasted time/energy that could�ve been devoted to reproductive output

13. Models of Competition descriptive mechanistic

14. Exponential Growth J curve dN/dt = rN r = intrinsic rate of increase

15. Logistic Growth Model S curve dN/dt = rN(1-N/K) dN/dt - population growth rate r - per capita rate of increase K - carrying capacity growth rate decreases as approaches K max. population size occurs when dN/dt = 0

16. Models of Competition Lotka (1925) & Volterra (1926) descriptive model developed with mobile animals in mind extended logistic model to include two-species competition

17. Lotka-Volterra Model dN1/dt = r1N1(K1-N1-?12N2)/K1 dN2/dt = r2N2(K2-N2-?21N2)/K2 main difference is a competition coefficient ?ij; effect of species j on species i How much does species j utilize the carrying capacity of species i?

18. Lotka-Volterra cont� if species I and J are equivalent competitors, ?ij = ?ji = 1; rarely happens if ?ij < 1 means effect of species j is less than effect of species i on its own members if ?ji < 1 means effect of species i is less than effect of species j on its own members

19. Zero Isoclines and State-space Graphs dN/dt or growth rate of selected species is set to 0 and you solve for N give values of N1 and N2 that yield zero population growth for each species the x axis represents abundance of species 1, and the y axis represents the abundance of species 2 points represent a combination of abundances of species 1 and 2

20. Zero Isoclines population is increasing left of isocline (below K) and decreasing right of isocline (above K) isocline for species 1 represents a combination of abundances of the two species where species 1 population does not increase or decrease

21. Different Outcomes

22. Arrangements of 2 Isoclines (1) competitive exclusion of species 2 by species 1 population of species 2 goes from 0 to negative under conditions in which species 1 can increase

23. Arrangements of 2 Isoclines (2) competitive exclusion of species 1 by species 2 population of species 1 goes from 0 to negative under conditions in which species 2 can increase

24. Arrangement of 2 Isoclines (3) both species have achieved zero growth (isoclines cross) and stable coexistence (initial abundances do not matter)

25. Arrangement of 2 Isoclines (4) isoclines cross, but whether species coexist depends on initial abundances of the species; unstable equilibrium

26. Lotka-Volterra Summary assumptions no migration K and ?ij are constants stable coexistence is possible only when intraspecific competition is greater than interspecific competition

27. Mechanistic Models of Competition incorporate resources express competition coefficients & carrying capacities as rates of utilization & resource renewal Under what conditions do we find coexistence of species?

28. The R* Rule R* - concentration of a resource when a population of a single species grown alone reaches its equilibrium density winner of competition is determined by which consumer species produces the lower value of R* in the absence of the other Essentially, who can maintain population at the lowest level of the limiting resource(s)?

29. Tilman�s Models of Competition multi-consumer, multi-resource models average mortality rate of each species assumed to be independent of density & resources supply rates of limiting nutrients population growth rates as a function of nutrient supply rates assumed to level off at high rates due to saturation competition occurs through the effect of each species on the consumed resources (consumptive)

30. Zero-growth IsoclinesCompetitive Exclusion

31. Zero-growth IsoclinesCompetitive Exclusion region 1 below minimum concentration needed to balance growth & mortality both go extinct regions 5 & 6 species B wins (lowest R*)

32. Reading Assignment Tilman, D. 1985. The resource ratio hypothesis of plant succession. American Naturalist 125: 827-852. We�ll discuss this paper next Monday, February 18.

33. Crossing of Zero-growth IsoclinesStable Coexistence region 1 � both go extinct species A: resource Y limits it most species B: resource X limits it most

34. Crossing of Zero-growth IsoclinesStable Coexistence CA and CB: consumption vectors or ratio in which the 2 resources consumed by each consumer species A & B consume resource that limits it the most at a greater rate than it consumes the non-limiting resource region 4 � stable coexistence

35. Crossing of Zero-growth IsoclinesUnstable Coexistence region 1 � both go extinct each species consumes resource that limits the other species the most at a greater rate than it consumes the resource most limiting to it region 4� � unstable coexistence

36. Competition between Algal Species two diatom species two resources: phosphate and silica R* is lower for silica than phosphate in Cyclotella phosphate limits Cyclotella the most

37. Competition between Algal Species two diatom species two resources: phosphate and silica R* is lower for phosphate than silica in Asterionella silica limits Asterionella the most

38. Outcome of Competition 1 - both go extinct 2&3 - Cyclotella wins 4 - stable coexistence 5&6 � Asterionella wins

39. Neighborhood Models of Competition Tilman�s models worked for phytoplankton resources more homogeneous don�t work well for terrestrial plant species spatial relationships are important to competitive outcome in plants 2 main types of models simulations that keep track spatially of plants analytical models that capture essence of spatially constrained competition

40. Neighborhood Models of Competition plants compete within neighborhoods focal plant responds to competitors within a surrounding area

41. Neighborhood Model of Intraspecific Competition within Arabidopsis thaliana Pacala and Silander (1985) fecundity reduced with number of neighbors

42. Two Species Neighborhood Model of Competition Pacala (1986) - 2 annual plant species without seed dormancy density of neighbors affects fecundity main point similar to Lotka- Volterra: coexistence where intraspecific competition > interspecific competition

43. Coexistence of Species some species fail to coexist those that do coexist, have interspecific differences in resource use even ecologically similar species differ to some degree

44. Meanings of Niche (1) Grinnell (1914) coined the term �no two species of birds or mammals will be found to occupy precisely the same niche� Hardin (1960) � competitive exclusion principle complete competitors (i.e., those that compete for EXACTLY the same resources in the same way) CANNOT coexist thus, species that do coexist must differ in resource utilization niche or resource partitioning, species packing

45. Meanings of Niche (2) Elton (1926) �what place a species occupies in a community� functional role of a species Hutchinson (1957) range of physical & biological conditions required by a species n-dimensional hypervolume: each axis corresponds to an individual physical or biological variable

46. Resource Partitioning species that coexist differ in some aspect of their lifestyle (n-dimensional hypervolume) MacArthur (1958) foraging differences of 5 warbler species in New Hampshire partitioning resources by specializing on different structural strata in the forest

47. Fundamental & Realized Niches fundamental physiological response curve, pre-interactive range of conditions in which a species can occur in the absence of competitors absence of other species in general, including facilitators realized ecological response curve, post-interactive range of conditions over which a species occur in the presence of competitors range will be reduced because competitive exclusion in areas of overlap with competing species

48. after Mueller-Dombois and Ellenberg (1974) competitors constrain species Z to its ecological response curve (realized niche) Fundamental & Realized Niches

49. Regeneration Niche Grubb (1977) one more way species can partition up the physical and biological hypervolume differences in phenology, timing of germination, microsite specialization