Evolutionary Responses of A Dominant Plant Along a Successional Gradient in A Salt-Marsh System

The ecological responses of plant populations along the successional gradient have been intensively examined; however, the evolutionary responses remain to be elucidated. Here, I explored genetic changes of key phenotypic traits of a dominant plant along a successional gradient, and whether these changes were induced by abiotic and biotic variables. I measured key abiotic (e.g. clay thickness) and biotic variables (e.g. herbivore density) along the successional gradient in the high and low marsh in a Wadden Sea saltmarsh. Also, I collected samples of Elytrigia atherica, grew them in the greenhouse, and measured key functional traits. I found that clay thickness (a proxy of total nitrogen) increased along the successional gradient both in the high and low marsh; herbivore density from hares (the most important herbivores) decreased along the successional gradient in the high marsh. Also, I found that growth in number of leaves and ramets decreased, while rhizome length increased, along the successional gradient for E. atherica collected from the high marsh. Opposite trends were found for E. atherica collected from the low marsh. Results suggest that, in the high marsh, herbivores may overrule nutrients to drive trait changes. That is, at early successional stages, E. atherica had higher growth in number of leaves and ramets to compensate for high-density grazing. In the low marsh, nutrients were the dominant driver for trait changes. These results suggest that ecologically important abiotic and biotic variables such as nutrients and herbivores may also have a substantial evolutionary impact on plant populations.

A socio-ecological landscape analysis of human–wildlife conflict in northern Botswana

Human–wildlife conflict is one of the most pressing issues in conservation. Low-income rural communities are disproportionately affected by negative interactions with large predators, which often leads to retaliatory killings and persecution of the animals. To overcome this, socio-ecological studies that merge existing knowledge of large predator ecology with long-term livestock depredation monitoring are required. We examined patterns and drivers of livestock depredation in northern Botswana, using a mixed effects model of the government's long-term monitoring data on human–wildlife conflict, to identify ways to reduce depredation at key spatial and temporal scales. We compared the results to farmers’ understanding of their personal risk within the landscape. We analysed 342 depredation events that occurred during 2008–2016, using variables measured at different scales. The variables affecting the locations of depredation events at the 2-km scale were distance to protected areas and predator and herbivore density, with increased depredation in the wet season. At a 1-km scale, herbivore density did not have a significant effect, but the effect of other variables was unchanged. The 4-km scale model was influenced by livestock and herbivore density, with increased depredation in the wet season. Livestock depredation could be reduced by establishing an 8-km livestock-free buffer along the protected area boundary. There was disparity between government data on human–wildlife conflict, depredation reported by farmers in interviews and farmers’ risk awareness. Farmers would benefit from workshops providing tools to make evidence-based decisions and minimize their risk of negative interactions with wildlife. This would ultimately contribute to wildlife conservation in the Kavango-Zambezi Transfrontier Conservation Area.

Effects of time delay and space on herbivore dynamics: linking inducible defenses of plants to herbivore outbreak

Empirical results indicate that inducible defenses of plants have effects on herbivore populations. However, little is known about how inducible defenses of plants have influences on herbivore outbreak when space effect is considered. To reveal the relationship between inducible defenses and herbivore outbreak, we present a mathematical model to describe the interaction of them. It was found that time delay plays dual effects in the persistence of herbivore populations: (i) large value of time delay may be associated with small density of herbivore populations and thus causes the populations to run a higher risk of extinction; (ii) moderate value of time delay is beneficial for maintaining herbivore density in a determined range which may promote the persistence of herbivore populations. Additionally, we revealed that interaction of time delay and space promotes the growth of average density of herbivore populations during their outbreak period which implied that time delay may drive the resilience of herbivore populations. Our findings highlight the close relationship between inducible defenses of plants and herbivore outbreak.