Insect herbivory may cause changes in the visual properties of leaves and affect the camouflage of herbivores to avian predators

Behavioral Ecology and Sociobiology - An individual’s metabolic competence is important when escalating to costly behaviours in agonistic encounters. The use of broken shells in the wild...     

Conditions under which plants help herbivores and benefit from predators through apparent competition

Leaf domatia are tiny structures in leaf vein axils that are typically inhabited by predatory and fungivorous mites. A recent article reported plant domatia specifically suited for herbivorous mites, which seems paradoxical, since the plant is thus supporting a natural enemy that can harm itself. The authors claimed that domatia are created to promote herbivorous mites as "fodder" for predatory mites that attack another herbivorous mite damaging the plant, and that the relationship among the plant, the fodder mite, and the predatory mite constitute a multiway mutualism because all three species benefit from the interaction. I formulate this system using two simple mathematical models of apparent competition, which differ in how domatia are modeled, and then assess when it is advantageous for the plant to create such space for a natural enemy. As a necessary condition for mutualism, the product of reproductive efficiency and nutritious value of the fodder prey should exceed that of the pest prey. This condition is also sufficient, if the direct costs for making the structure of domatia are negligible. If there are significant costs, however, the condition is broader for predators with lower reproductive efficiency and higher mortality, and for non-fodder prey with high consumption rate and low predation rate. I suggest that creating domatia is more effective when predators are less prolific and non-fodder prey are more severe as pests. Finally, I discuss how this mathematical model can apply to a wider range of tritrophic mutualistic relationships such as those among plants, aphids, and ants.     

Warning signals confer advantage to prey in competition with predators: bumblebees steal nests from insectivorous birds

Aposematic (warning) signals of prey help predators to recognize the defended distasteful or poisonous prey that should be avoided. The evolution of aposematism in the context of predation has been in the center of modern ecology for a long time. But, the possible roles of aposematic signals in other ecological contexts have been largely ignored. Here we address the role of aposematic signals in competition between prey and predators. Bumblebees use visual and auditory aposematic signals to warn predators about their defenses. For 2 years, we observed competition for nestboxes between chemically defended insects, Bombus ardens (and possibly also Bombus ignitus), and cavity nesting birds (Parus minor and Poecile varius). Bumblebees settled in 16 and 9 % of nestboxes (in 2010 and 2011 breeding seasons, respectively) that contained bird nests at the advanced stage of nest building or at the stage of egg laying. Presence of bumblebees prevented the birds from continuing the breeding activities in the nestboxes, while insects took over the birds’ nests (a form of kleptoparasitism). Playback experiments showed that the warning buzz by bumblebees contributed to the success in ousting the birds from their nests. This demonstrates that aposematic signals may be beneficial also in the context of resource competition.     

Chemical defense in pelagic octopus paralarvae: Tetrodotoxin alone does not protect individual paralarvae of the greater blue-ringed octopus (Hapalochlaena lunulata) from common reef predators

Some pelagic marine larvae possess anti-predator chemical defenses. Occasionally, toxic adults imbue their young with their own defensive cocktails. We examined paralarvae of the greater blue-ringed octopus (Hapalochlaena lunulata) for the deadly neurotoxin tetrodotoxin (TTX), and if present, whether TTX conferred protection to individual paralarvae. Paralarvae of H. lunulata possessed 150 ± 17 ng TTX each. These paralarvae appeared distasteful to a variety of fish and stomatopod predators, yet food items spiked with 200 ng TTX were readily consumed by predators. We conclude that TTX alone does not confer individual protection to paralarvae of H. lunulata, and that they possess an alternative defense. In larger doses, tetrodotoxin is a deterrent to the predatory stomatopod Haptosquilla trispinosa (mean dose = 3.97 μg/g). This corresponds to 12–13 paralarvae per predator based on the TTX levels of the clutch we examined. Thus, the basic assumption that individual paralarvae of H. lunulata are defended by TTX alone was disproved. Instead, functionality of TTX levels in paralarvae may arise through alternative selective pathways, such as deterrence to parasites, through kin selection, or against predator species not tested here.