Mutualism, herbivory, and invasive ants as seasonally dependent drivers of root surface area in a foundational savanna ant-plant.

Many plants are defended from herbivory by costly insect mutualists. Understanding positive associations between plants and mutualists requires a whole-plant perspective including roots. We hypothesized that root surface area increases with mutualist activity (to a saturation threshold) and recent rainfall but that this relationship shifts when herbivores are excluded.

The impact of shade on whole-plant carbon allocation in a dominant East African tree sapling.

Plasticity in resource allocation can be beneficial for plants under stress. In savannas, tree-grass competition forces tree saplings growing in the grass layer to compete for water, nutrients, and light. Savanna tree saplings are also vulnerable to fire and herbivory, which may favour investment in storage belowground to support regrowth aboveground.

Disruption of an ant-plant mutualism shapes interactions between lions and their primary prey.

Mutualisms often define ecosystems, but they are susceptible to human activities. Combining experiments, animal tracking, and mortality investigations, we show that the invasive big-headed ant () makes lions () less effective at killing their primary prey, plains zebra (). Big-headed ants disrupted the mutualism between native ants ( spp.

Symbiotic ant traits produce differential host-plant carbon and water dynamics in a multi-species mutualism.

Cooperative interactions may frequently be reinforced by "partner fidelity feedback," in which high- or low-quality partners drive positive feedbacks with high or low benefits for the host, respectively. Benefits of plant-animal mutualisms for plants have been quantified almost universally in terms of growth or reproduction, but these are only two of many sinks to which a host-plant allocates its resources. By investigating how partners to host-plants impact two fundamental plant resources, carbon and water, we can better characterize plant-partner fidelity and understand how plant-partner mutualisms may be modulated by resource dynamics.

Mutualism disruption by an invasive ant reduces carbon fixation for a foundational East African ant-plant.

Invasive ants shape assemblages and interactions of native species, but their effect on fundamental ecological processes is poorly understood. In East Africa, Pheidole megacephala ants have invaded monodominant stands of the ant-tree Acacia drepanolobium, extirpating native ant defenders and rendering trees vulnerable to canopy damage by vertebrate herbivores. We used experiments and observations to quantify direct and interactive effects of invasive ants and large herbivores on A.

Frenemy at the gate: Invasion by Pheidole megacephala facilitates a competitively subordinate plant ant in Kenya.

Biological invasions can lead to the reassembly of communities and understanding and predicting the impacts of exotic species on community structure and functioning are a key challenge in ecology. We investigated the impact of a predatory species of invasive ant, Pheidole megacephala, on the structure and function of a foundational mutualism between Acacia drepanolobium and its associated acacia-ant community in an East African savanna. Invasion by P.

Left out in the cold: temperature-dependence of defense in an African ant-plant mutualism.

Many tropical plants are defended by ants, and the costs and benefits of these mutualisms can vary across gradients of herbivory, soil fertility, latitude, and other environmental factors. Yet despite an abundant literature documenting thermal constraints on ant activity and behavior, we know little about whether temperature variation can influence the benefits conferred by ants to plants. We evaluated the effects of dawn-to-dusk fluctuations in temperature on patrolling and aggressive behavior in four arboreal ant mutualists of Acacia drepanolobium trees in central Kenya.