Question

Which statement about zero population growth isoclines of two competing species is true?

1) Species coexistence requires that the two isoclines cross.
2) The crossing of the two isoclines is a sufficient condition for species coexistence.
3) If the species coexist, they will each do so at a higher density than either would if placed alone.
4) Both a and c

Answer 1

Species coexistence requires that the isoclines cross, which is necessary but not sufficient for coexistence. The crossing does not ensure higher densities than if each species were alone; other factors also affect coexistence.

Step-by-step explanation:

The question pertains to the concept of zero population growth isoclines in the context of two competing species, which relates to the Lotka-Volterra competition model in ecology. An isocline represents all the points where a particular species' population remains constant due to a balance of factors such as birth and death rates. To achieve species coexistence, the zero population growth isoclines for two species must cross; however, this is only a necessary condition, not a sufficient one. Coexistence is also determined by other factors such as resource allocation and interference competition.

Option 1 states that the crossing of the isoclines is necessary for coexistence, which is correct. Option 2 incorrectly suggests it is sufficient. Option 3 is not necessarily true as species may compete for resources leading to reduced densities compared to when each species is alone. Therefore, the final answer is that option 1 is true: Species coexistence requires that the two isoclines cross. Option 4 is incorrect because it includes the inaccurate statement of option 3.