Environment

How come there are so many plants?

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Margalef often spoke of the Baroque of nature. The enormous diversity of living beings makes one think that it is as if nature had horror of emptiness. Sandra Díaz, the second woman to win the Ramon Margalef International Prize for Ecology, spoke of this idea. She is a scholar of functional types, which synthesize the enormous diversity of the plant world by grouping species on the basis of functional traits (often linked to physiognomic traits or sometimes biochemical, physiological, etc. (e.g. seed weight, leaf surface and thickness, proportion C/N in leaves, etc.). Functional types are useful when making models.

Although insects, for example, present an overwhelming diversity, it can be imagined linked to the variety of resources (different types of leaves and fruits, other animals, decomposing residues, pollen, etc.). But the plants all use the same resources: light, water and nutrients from the soil, and yet in a dry meadow 40-60 species of grass can be found in 1 m2 and in a tropical forest 300 species of trees in 1 ha . If all use the same resources, it seems to contradict the principle of competitive exclusion (according to which, if two species use the same resource, the most efficient eliminates the other).

The classic explanation is that, at each point, available resources and environmental variables vary and that species ‘ life cycles develop differently and reach different sizes and longevities. However, in the case of the little herbs, we find them very close together, of similar size, and they live their whole cycle simultaneously. Therefore, the traditional explanation is incomplete.

To explain the high diversity of trees in tropical forests, Janzen said that the selection favored dispersion at a certain distance so as not to provide facilities for specific phytophages and pests. In addition, Peñuelas and his team have shown that the composition of the plants involves multiple nutritious elements in varying proportions and this also justifies diversity: the species differ biogeochemically depending on whether they are more or less flexible in this respect, whether they live together or not (if they do, competitive pressure causes their biogeochemical behavior to diverge more) and whether they have more or less similar genomes.

The division of plant biodiversity into functional types makes it possible to work with simplified models and is a first step towards clarifying the Baroque of nature and the non-compliance with the principle of competitive exclusion. The explanation of diversity within each type requires, however, a second level of explanation considering average habitat conditions, fluctuations, life cycles, biogeochemical organization and interactions with competitors, herbivores, parasites, etc.

Functional types are very useful in a wide range of topics (for example, for models of response to fires or climate change), but the Baroque of nature persists and each of the hundreds of thousands of plant species has its own more or less plastic characteristics that we are largely unaware of.

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