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NRES 310 lecture Niche dynamics 5 November 2007 1 Forms of interactions between species. Competition: each species has a negative effect on the other, does not need to be balanced. Commensalism (facilitation): one species benefits without affecting the other. Mutualism: both species benefit Predation & parasitism: one species benefits to the disadvantage or detriment of the other NICHE DYNAMICS Any discussion of competition must begin with the concept of ecological niche. Niche: functional role and position of the organism in its community. Habitat is address, the niche is job. Niche must include every aspect of the environment that limits the distribution of the species. Hutchinson hypervolume multidimensional # axes (correspond to independent physical or biological variables that affect the abundance of that species) that make up the niche of an animal. defined by the set of resources and environmental conditions that allow a single species to persist in some particular region. Used niche to describe the range of physiological and biological conditions, including limiting resources needed for a species or population to maintain a stable or increasing population size. 2 Temperature NRES 310 lecture Niche dynamics 5 November 2007 Foraging height Seed size Foraging height Seed size Cannot draw all or dimensions on a graph, but you can envision a sphere that theoretically completes the niche. Problem: This approach assumes we know what to measure, we often measure what we can rather than what is important or we measure so many things that the important variable is lost in the chaos. Habitat Use: is uniquely defined by what is available. Habitat Selection: Used – Available (+ result is selection, - is avoidance, 0 used proportional to availability.) Niche is often dealt with in terms of what is available. ** If habitat selection is related to survivorship and fecundity then it is linked to population dynamics (never been documented). 1. If you just look at use to describe niche dynamics, then you cannot evaluate what is available. 2. Use and Availability, may miss importance, because something very important may be used in proportion to what is available and you would not be able to document or evaluate it. 3. Importance = use x availability (rescaled to 100%). 4. Consider: USE, SELECTION, and IMPORTANCE 5. THEN you may be able to deal with niche. NICHE 1. Fundamental niche – full range of variables to which it is adapted, an area that an animal would occupy in the absence of competitiors. NRES 310 lecture 3 Niche dynamics 5 November 2007 a. Set of resources and environmental conditions that allow a single species to persist in a particular region, often conceived as a multidimensional space. b. This is rarely, if ever, seen in nature because the presence of competing species restricts a given species to a narrower geographic range of conditions. 2. Realized niche – area that an animal occupies in the presence of competitors. a. Set of resources and environmental condition constrained by competition or predation that allow a single species to persist in a particular region. b. Interspecific competition excludes a species from certain areas of its fundamental niche. Fundamental niche Realized Niche in the presence of 5 superior competitors Competition is dependent upon the number of competitors and how much niche overlap among them. Ecologists usually confine themselves to one or two niche dimensions, such as feeding, and space use. Niche of an animal can change over time. Example : insects with complex life-histories can occupy one niche as larvae and another as an adult. Fish, niche space changes as the organism matures by size (switches from plankton when small to eating small fish as grows). Also changes Interspecific relationships ie. Interspecific competition. Principle of Competitive Exclusion: postulated by Gause 1934. Complete competitors cannot cowxist.as a result of competition two species hardly ever occupy NRES 310 lecture 4 Niche dynamics 5 November 2007 similar niches, but displace each other in such a manner that each takes possession of certain kinds of food and modes of life in which is has an advantage over its competitors. Basically 2 species cannot occupy the same niche. Untestable because it cannot be disproved, because either result exclusion or coexistence can be attributed to the principle. frequency frequency Intraspecific competition diet Interspecific competition diet At some point intraspecific competiton > interspecific competition because individuals have the same demands for resources. Resource Partitioning or “Ghost of Competititon Past” For example: today we measure the niche of two similar species that are sympatric and detect no measured differences: So is it past competition resulting in narrower niche OR physiological differences let animals fit together in the absence of competition. Possibly both are true, but it is impossible to measure with correlation studies. Only demonstrable with removal experiments. 2 possible outcomes of competition Competitive exclusion can occur particularly with species without evolutionary history together. NRES 310 lecture Niche dynamics 5 November 2007 5 Co-existence more common with natural communities. Example: National Bison Range Mountain Goats Forested benches – mule deer Steppe grasslands elk Bighorn sheep Prairie – Bison and pronghorn Riparian White-tailed deer Grasseaters – bison, elk, sheep spatial diversity where dietary niche overlaps. Forbeaters – white-tailed deer, mule deer, pronghorn, goats Spatial separation dietary niche overlap is greatest Spatial overlap dietary separation NRES 310 lecture Niche dynamics 5 November 2007 6 This is especially true is spatial overlap can occur. To find out if competition is occurring you must find a way to separate niche axes. NICHE EXCLUSIVITY – Opimality Models or Optimal foraging models. Bison Body size, Bite size, & Handling time Bison & deer Deer Bison, deer, & rabbits Deer & rabbits Rabbits Zones of niche exclusivity Bison, deer, rabbits, & voles Deer, rabbits, & voles Rabbits & voles Voles everybody Deer, rabbits, voles & grasshoppers Rabbits, voles, grasshoppers Voles & grasshoppers Grasshoppers Quality and Abundance of Vegetation *No population dynamics included *could add sexual segregation (for body size, bite size relationships) *species with small bite sizes are regulated to high quality food. *allometric relationships determine zones of competition Get co-existence based on zones of exclusivity – allows exclusivity and competition. Optimal energy maximizing v. time minimizing strategies. Old models do not include predation. New Models bring in predation. What are the units of selection? Energy? Protein? A: successful reproduction May be good for looking at niche theory. Niche exclusivity and niche partitioning, but it makes removal experiments too simple. It does provide ideas for experiments and allows for ideas to model niche partitioning. Remember predation is not included here. Most species need to avoid predators and they reduce predation by utilizing “enemy-free space” NRES 310 lecture Niche dynamics 5 November 2007 Enemy free space does not refer to a particular location, but rather the set of conditions that minimize the impact of predators, in a similar manner to how niche refers to the set of conditions that allows species to co-exist. Need to briefly discuss apparent competition Defn: a species entering a community is similar enough to another that even if they do not directly compete the two species together can support greater predator populations that one alone, which has a greater negative impact on both species by predators than would if either occupied the area alone. 7