Lectures on species interactions and competition

Situation where the isoclines cross
Interesting patterns can occur depending on the relationship of the isoclines to each other:
• When the isoclines cross with K 1
exceeding K 2
/ . , each species limits the other more than it
does itself), population trajectories are such that stable equilibrium points exist at both
species carrying capacities, K 1
and K 2
.
• If K 1
is less than K 2
/ . , (i.e., if each species limits itself more than it limits the other
species), then there is a stable equilibrium at the intersection of the isoclines and both
species can coexist. The most obvious way for this to happen is through niche separation.
Conclusion: It is very difficult for species to coexist at equilibrium, unless each species
limits itself more than it limits the other.
However, natural populations may not come into equilibrium very often, or other interactions
may limit the full competitive interaction between species. • Tilman 1982