1. Ecology: Lecture 13 Interspecific Competition 2 November 5, 2007

2. Definition of a niche: Theodore Giesel And NUH is the letter I use to spell Nutches, Who live in small caves, known as Niches, for hutches. These Nutches have troubles, the biggest of which is The fact there are many more Nutches than Niches. Each Nutch in a Niche knows that some other Nutch Would like to move into his Niche very much. So each Nutch in a Niche has to watch that small Niche Or Nutches who haven't got Niches will snitch. -On Beyond Zebra (1955)

3. Definition of a niche (from Hutchinson and Shelford)  For each environmental variable it faces in its world, an organism has a range of values for which it can grow and multiply

4. A space of n-dimensions

5. Defining and mapping niches (based on key characteristics)

6. Niche relationships among species x-axis: state of a particular resource (size of prey, for example) y-axis: species response/fitness (much as for Shelford’s law of tolerance)

7. Niche overlap: mapping >1 variable

8. Fundamental vs. realized niche

9. Competitive exclusion principle  Gause: “As a result of competition, two similar species scarcely ever occupy similar niches, but displace each other in such a manner that each takes possession of certainly particular kinds of food and modes of life in which it has an advantage over its competitor.”  Hardin: “Complete competitors cannot coexist.”

10. Resource partitioning

11. Resource partitioning: Mojave desert plants

12. Resource partitioning: Christmas Island terns

13. Other responses to competition (spatial rather than resource-based)  Niche compression  Example: Doves in New Guinea  Niche shift  Example: Sunfish in artificial ponds  Ecological release

14. Character displacement: Darwin’s finches

15. So, how is it possible for so many similar species of tropical fish to exist?

16.  Explanations consistent with the competitive exclusion principle  i.e. resource partitioning, niche compression, niche shift  Essentially, these suggest extreme specialization  Multiple niche dimensions must be considered (see. Fig. 14.21)  What might some of these “dimensions” be?

17. So, how is it possible for so many similar species of tropical fish to exist?  Non-equilibrium conditions  Factor 1: Transient nature of larvae  What does this mean?  How could this prevent competitive exclusion?  Factor 2: Environmental disturbance (i.e. storms)  Cause mortality  How could this prevent competitive exclusion?  Factor 3: Predation!  Predators may target the species that are most abundant, so that less abundant species are able to increase.  How can we relate this back to the Lotka- Volterra competition equations?