Environment, Ecology & Earth's biodiversity

[Sully]

A look on grazing lawns, their nutrient cycles and how rainfall and predators can impact these and the size of herbivores who inhabit them (from: Predators and rainfall control spatial biogeochemistry in a landscape of fear)

"Rainfall could become a mitigating factor by determining the size range of herbivores that occupy a specific grazing lawn, and accordingly the ratio of N that is released there. Rainfall increases the quantity of grass that is produced. However, that grass has poorer quality, making it harder to digest. Larger herbivores stand to disproportionately benefit from this because they require high quantities of forage, plus they have the physiological adaptations to digest poorer-quality forage (16). Smaller herbivores, alternatively, require less quantity, but their digestive adaptations necessitate that they seek high-quality forage (16). Thus, the mean body mass of herbivores present on a given lawn should increase along a gradient of increasing rainfall (Fig. 1B). That is, grazing lawns with lower rainfall (higher forage quality) should be frequented by herbivores from the smaller end of the size range, whereas lawns with higher rainfall (higher forage quantity) should be occupied by herbivores from the larger end of the size range. 

Now predators could complicate the matter by further determining which sizes of herbivores occupy a given grazing lawn. In savanna ecosystems, susceptibility of herbivore prey to predation decreases with herbivore body mass (Fig. 1C), with the very largest species even being completely invulnerable to predation (17, 18). Consequently, smaller herbivores should be more fearful than large herbivores, and therefore be more inclined to avoid grazing lawns that pose high risks of being captured by predators. Risky grazing lawns tend to be those surrounded by high vegetation because it hides predators that wait in ambush (19). Hence, more open grazing lawns should attract herbivores from the smaller end of the size range because the greater visibility makes them less risky places to feed (19). 

Taken together, the amount of rainfall and level of potential predation risk should create a joint gradient in the sizes of herbivores occupying different grazing lawns, thereby offering a way to explain spatial contingency in biogeochemical properties across landscapes. High-rainfall, high-risk sites should have the highest proportion of large herbivores. That proportion should dwindle as rainfall and risk become lower (Fig. 1D). Such patterning in herbivore size should then determine patterning in associated landscape biogeochemistry (Fig. 1E) due to the size dependence of N released in dung. By virtue of fast nutrient recycling, the size dependence of released N should be further reflected in the patterning of N in grass foliar tissue (Fig. 1E)."

Edit: The emojis are supposed to be Nitrogen: Phosphorous but wildfact automatically makes colonP an emoji lol Reply