Large-bodied mammals living in fragmented habitats are at higher risk of extinction, and such risk can be influenced by ecological factors such as predator-prey system dynamics. These dynamics can be particularly complex for conservation management when one endangered species is known to prey on another endangered species within the confines of isolated or poor-quality habitats. Here we describe predation events observed over 19 months involving two threatened species: the largest carnivore found in Madagascar, the fosa (Cryptoprocta ferox), and three groups of diademed siafaka (Propithecus diadema) in the Betampona Strict Nature Reserve. This site is a 22 sqkm low-altitude rainforest surrounded by agricultural land and isolated from larger forest corridors; the consequences of predator-prey dynamics can have important implications for conservation at this site. We report five direct observations of fosa predation attempts, of which one was successful, the discovery of the body of a sifaka with evidence of fosa predation, and the disappearance of three individuals. We describe the attacks and compare the sifaka activity budgets and movement patterns before, during, and after the events. The sifakas’ strategy to escape the predator is fleeing short distances, hiding, and remaining vigilant. Our observations suggest that fosa predation impacts the survival and reproduction of diademed sifakas in Betampona. The impact of predation on the diademed sifaka population of Betampona, combined with low reproductive rates and potential high inbreeding due to the isolated condition, can have important consequences on the survival of this species at this site. Given the compounding effects of habitat isolation and high hunting pressure, conservation management plans should incorporate predator-prey dynamics by assessing estimates of prey and predators’ population densities over time, as well as quantify the incidence of predation pressure on prey population to devise effective conservation strategies at the community level.

Predation can take unexpected turns. For instance, various invertebrate species - most commonly spiders - may prey on tetrapods. Here, we report observations of spiders (Sparassidae, Olios sp.) preying on amphibians (Hyperoliidae, Heterixalus andrakata) in north-eastern Madagascar. To do so, the spiders built highly-specialized traps by weaving two leaves together. Four cases by different individuals of the same species show that spiders hide at the rear end of the trap. One case reports the feeding on a small frog caught inside the trap. Previous reports on amphibian predation by spiders describe opportunistic and indiscriminate predation behaviour by generalist ground-dwelling or aquatic spiders. The only more targeted cases concern large orb-weaver spiders building large webs that may serve as an effective trap for small vertebrates, but those only make up a small percentage of prey compared to insects. In contrast, the novel traps type reported here seems to be solely targeted at catching amphibians seeking shelter during the daytime. We thus report systematic trapping of amphibian by spiders, a newly recorded behaviour.