researchers explore how herbivore activity around water affects plant communities | UCSB


Plants need water to grow. So if there is water, shouldn’t there be more plants? New research from UC Santa Barbara and the Mpala Research Center in Laikipia, Kenya shows it’s much more complicated than that.

“You might think that water sources in drylands have more plants,” said lead author Georgia Titcomb, postdoctoral researcher at UCSB. “We have found that in really arid places the herbivores come and get water, trample and eat the plants, so there is a lot more bare soil or very well suited grass grasses.” But this is not the case everywhere in the savannah.

Researchers gathered data from waterhole communities over the course of two years to study how herbivore activity affects vegetation in the savannas of central Kenya. They determined that the impacts depend very much on environmental conditions. Their study appears as a cover story in the journal Ecological Applications.

Titcomb is actually a disease ecologist interested in the transmission of parasites and pathogens in wild and domestic animals. She was curious as to how water sources could group animals together in such a way as to promote disease transmission.

She concluded that a key step to understanding this was to characterize the plant communities around water sources, as plants are an important vector for many pests as well as a crucial resource for the animals themselves. After some preliminary analysis, Titcomb realized that this research would augment previous herbivore and plant ecology studies conducted in the region.

The team surveyed 17 pairs of sites a total of four times each over a two-year period. They matched each water source to a control site one kilometer away that had similar environmental conditions.

The researchers counted the diversity and height of vegetation around water points and at control sites, and identified herbivore activity based on the feces. They also characterized the nutrients and physical composition of the soil at each site.

Fieldwork around the water points presented a number of challenges. For example, researchers also had to accommodate wildlife. “We had to stop work when the elephants came, for example, and let them drink at the watering hole,” recalls Titcomb. “It was like, ‘Okay everyone, get off the transect line, get in the car and wait.'”

The authors found that the effect of herbivores on plant communities around these water sources differed depending on the context. Under favorable conditions for plants, plant diversity increased near water. This is probably due to the fact that herbivores controlled the species that would otherwise dominate the area.

This allowed other plant species to gain a foothold, although the animals ate more vegetation throughout the area.

Meanwhile, under more arid conditions, the increased activity of herbivores around the water resulted in a decrease in the number of plants and plant species. Titcomb believes this is because there simply aren’t enough resources for plants to be so resilient in these areas.

Only the hardiest species were able to withstand these conditions and pressures. Usually these were important grasses that formed pasture lawns frequented by both wildlife and livestock.

The results built on previous research on these water sources, which has often been carried out in even more arid regions of the savannah, Titcomb said. Previous studies have generally found that areas around water sources were bare of plants with depleted plant diversity. This article extends these results, showing that these plant communities exist along a spectrum based on the environmental conditions of the region.

Due to the nature of the fieldwork, there were a number of related factors that the authors were unable to disentangle in this study. Water collects in particular places, influencing soil composition, nutrients, and drainage, which also affect plant growth. Water also attracts herbivores, which in turn affect the survival of plants when they feed or trample on them. All these dynamics are linked.

Detecting the independent contributions of each of these factors would require controlled experiments. Nevertheless, the authors believe that this study is an important first step in understanding these systems.

“This work offers critical insight into how changing patterns of animal movement and aggregation – such as the herding of animals at water points – can change entire communities and ecosystems,” explained the co -author Hillary Young, professor of ecology at UCSB.

“However, it also shows that these changes are difficult to predict, and the size and even the direction of the effect can change depending on local environmental conditions, especially the climate,” Young said.

“Humans are changing every part of our environment,” Titcomb added. “We are reshaping the landscape, so it will be important to have some knowledge of these effects on plant communities when thinking about the management of wildlife and domestic animals. “

Humans are not only changing the physical environment, we are also changing the makeup of the herbivores that live in these spaces, she pointed out. For many regions, mixed use – such as cattle grazing and conservation – is the only viable way to support and protect the wildlife and landscapes in which it lives.

It can be very difficult to maintain a wildlife preserve without additional income, explained Titcomb. These findings can inform wildlife management efforts alongside livestock.

“Work like this – which takes into account both changes in environmental conditions and animal movements – will be essential to understanding and managing ecosystems in this era of global change,” Young said.

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