Step 1: Understanding the Question.
The question asks about the contributions of Alexander von Humboldt to ecological science, focusing on the relationship between species and their environment.
Step 2: Analyzing the Options.
(A) The relationship of species distribution: Correct — Humboldt was one of the first to describe how species are distributed across different geographic regions and the environmental factors influencing this distribution.
(B) Population growth equation: This was not a primary focus of Humboldt's work. This concept is more associated with figures like Malthus.
(C) The principle of limiting factors: Humboldt did discuss environmental limits, but his primary focus was on species distribution.
(D) Ecological biodiversity: While Humboldt contributed to understanding ecosystems, this term is more associated with later ecological studies.
Step 3: Conclusion.
The correct answer is (A) The relationship of species distribution, as Humboldt is known for his work on species distribution and the factors affecting it.