The Niche: Species Coexistence PDF

The Niche SPECIES COEXISTENCE Learning Objectives 1. Define the term niche, and describe its importance in species coexistence. 2. List some common limiting resources for organisms. 3. Explain the role of competition for limiting resources in defining species’ niches. 4. Differentiate between the...

The Niche SPECIES COEXISTENCE Learning Objectives 1. Define the term niche, and describe its importance in species coexistence. 2. List some common limiting resources for organisms. 3. Explain the role of competition for limiting resources in defining species’ niches. 4. Differentiate between the fundamental niche and the realized niche. 5. Provide one or more examples of niche differentiation between species. What is Ecology? Ecology is the study of: • the distribution and abundance of organisms • the interactions among organisms (= biotic interactions) • the interactions between organisms and their non-living environments (= abiotic interactions) Community Ecology studies mechanisms of coexistence. Community ecology is… The study of biodiversity. The study of biotic interactions (+, -, 0). Requires the coexistence of 2 or more species! How do species coexist? Each species occupies a niche. Niche: the role of an organism in its environment. ◦ The niche describes the range of physical and biological conditions, including limiting resources, needed for a species to maintain a stable or increasing population size. The niche can be restricted by competition Competition: -/- An antagonistic interaction in which both species experience a negative impact. ◦ Competition can only occur for limiting resources. ◦ May act as a force of natural selection if the resources are critical for survival, growth, or reproduction. Competition is often important in the acquisition of: ◦ ◦ ◦ ◦ ◦ ◦ Space Food (animals) Mates (animals) Water (mostly plants, sometimes animals) Nutrients (plants) Light (plants) … but many more limiting resources may be important! Principle of Competitive Exclusion Principle of competitive exclusion: Two species cannot coexist indefinitely if they rely on the same limiting resources and exploit them in the same way. In other words… if two species are competing for the same resource at the same time, the species acquiring and using a resource more effectively (the more competitive species) will eliminate the less competitive species. Species abundance (population size) Visualizing the Niche: abundance (species population size) vs resource. Resource gradient (e.g. food particle size, light availability, etc.) Species abundance Visualizing the Niche INTRAspecific competition for resource only. WITHIN SPECIES. (between individuals of same species) “blue spp.” Resource gradient (e.g. food particle size, light availability, etc.) Visualizing the Niche Species abundance NO INTERSPECIFIC competition for resource (no competition between members of different species. INTRAspecific competition within each!) “blue spp.” “red spp.” Resource gradient (e.g. food particle size, light availability, etc.) Low interspecific competition Species abundance LOW interspecific competition for resource (small overlap in resource use) “blue spp.” “red spp.” Resource gradient (e.g. food particle size, light availability, etc.) High interspecific competition HIGH interspecific competition for resource (large overlap in resource use) Species abundance Too much overlap in resource use = not enough resources acquired = negative population growth “blue spp.” “red spp.” Resource gradient (e.g. food particle size, light availability, etc.) Competitive Exclusion…? HIGH interspecific competition can yield Competitive Exclusion… Species abundance Too much overlap in resource use = not enough resources acquired = negative population growth – “blue spp.” eliminated. “blue spp.” “red spp.” Resource gradient (e.g. food particle size, light availability, etc.) Or adjust the niche? Species abundance INTERSPECIFIC competition for resource FUNDAMENTAL Niche (larger) REALIZED Niche (smaller) Resource gradient (e.g. food particle size, light availability, etc.) Fundamental vs Realized niche Fundamental niche: the range of conditions and resources an organism can tolerate and use. Realized niche: the range of conditions and resources the organism actually uses due to restrictions that occur in nature. Fig. 45.12, p. 1147 Niche partitioning between roots of different plants. • Bristly foxtail relies on surface nutrients and water. It is more at risk for drought, but can grow and reproduce quickly. • Smartweed may require time and energy to grow deep roots, and will compete with other spp. while growing, but will eventually access unique soil resources. • Mallow is intermediate. It will coexist well with foxtail, but may compete with smartweed. Fig. 45.13, p. 1148 Let’s Try It! • Which of the following would you expect to experience the most competition? • Which would experience the least competition? Genner et al. 1999. Ecology Letters 2: 185-190 Let’s Try It! • Which of the following would you expect to experience the most competition? • Which would experience the least competition? Genner et al. 1999. Ecology Letters 2: 185-190 Let’s Try It! • Which of the following would you expect to experience the most competition? • Which would experience the least competition? Genner et al. 1999. Ecology Letters 2: 185-190