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Ecological Competition Dynamics and Coexistence Strategies

Explore interspecific competition and population interactions through the logistic and Lotka/Volterra models. Discover the implications of competition coefficients and isocline modeling, leading to insights on species growth and coexistence strategies. Delve into outcomes of competitive scenarios and the concept of diffuse competition.

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Ecological Competition Dynamics and Coexistence Strategies

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  1. Interspecific Competition

  2. Population interactions

  3. # individuals Time Logistic Curve

  4. Logistic model • Logistic equation • dN/dt = rN((K-N)/K) • Assumptions of the logistic model: • Each individual has identical ecological properties • Instantaneous response to environmental change • Constant upper limit to population size and rate of gain is directly related to remaining gap • Limited space and constant food supply • Age distribution is stable

  5. Lotka/Volterra model • dN1/dt = r1N1[(K1-N1- 12N2)/K1] •  is the competition coefficient • 12 is effect of species 2 on species 1 • dN2/dt = r2N2[(K2-N2- 21N1)/K2] • if 12 >1, then individuals of sp. 2 have a greater inhibitory effect on individuals of sp. 1 than does species 1 on species 1. • if 12 <1, then sp. 2 individuals have less effect

  6. Lotka/Volterra assumptions • Environment is homogeneous and stable • Migration is unimportant • Coexistence requires a stable equilibrium point • Competition is the only important biological interaction

  7. Model with isocline Growth is 0 along the line See Fig. 12.1 and 12.2 Species 1 growth Species 2 growth

  8. Finding K/ • dN1/dt = r1N1[(K1-N1- 12N2)/K1 • if growth is 0, and r is >0, then the term (K1-N1- 12N2) must be 0 • therefore N1 = K1 - 12N2 • when N1 = 0, N2 = K1/12

  9. Possible outcomes Fig. 12.3

  10. Possible outcomes Fig. 12.3

  11. Competition - 2 species

  12. Competition - 3 species

  13. Diffuse competition • Effect of several species

  14. Diffuse competition • Effect of several species • Exclusion may occur

  15. How does coexistance occur? • Unpredictable gaps: the poorer competitor is a better colonizer • Unpredictable gaps: the pre-emption of space • Fluctuating environments • Ephemeral patches with variable life-spans • Aggregated distributions

  16. If we observe niche differences in the field, what does it mean? • Current competition • Evolutionary avoidance through competition • Evolutionary avoidance (without competition)

  17. DeWitt diagrams • Plants sown at different densities (40:0, 30:10, 20:20, 10:30, 0:40) • Seeds harvested

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