Increased seed predation in the second fruiting event during an exceptionally long period of community‐level masting in Borneo

Abstract

In Southeast Asian tropical rainforests, community‐level masting (CM) occurs at irregular intervals of 2–10 years. During CM periods, many plant species from various families synchronously flower and subsequently undergo community‐level fruiting. Seed predation is a key factor in understanding the ecological and evolutionary factors affecting CM. Masting is proposed to decrease seed mortality due to predation in two ways: by depressing predator abundance through extended and unpredictable absences of seeds; and by satiating predators via mass seed production (predator satiation hypothesis). If the hypothesis is valid in these rainforests, the incidence of seed predation will be higher in a fruiting event that occurs soon after a previous fruiting event, because the intervening period of seed absence would be inadequate to starve the predators. In this study, we examined seed predation by insects, focusing on five dipterocarp species that exceptionally reproduced twice during an extended CM period. All of the five species suffered more intense seed predation in the second fruiting event, consistent with the prediction expected from the predator satiation hypothesis. Weevils, bark beetles and mammals were the main cause of increased seed predation in three, one and one plant species, respectively. However, seed predation intensity did not increase during the second fruiting event in a few combinations of predator and plant species. We discuss the possibility that competition for seeds among predators and/or the interspecific differences in life history traits among predators might affect the varying intensities of seed predation among dipterocarp species by different seed predators.

Implications of a long‐term mast seeding cycle for climatic entrainment, seedling establishment and persistent monodominance in a Neotropical, ectomycorrhizal canopy tree

“…In the case of D. corymbosa , preliminary evidence supports a role for predator satiation due to the significantly higher proportional predation during low seed years relative to mast years. Given the absence of a vertebrate‐based seed dispersal mechanism in D. corymbosa , the low phytochemical defense compounds of D. corymbosa seeds (Henkel et al, ), along with current seed predation performed largely by insects, it is conceivable that invertebrate predator selection pressure may have been a driver for a predator satiation mechanism, as recently posited for Bornean dipterocarps (Iku et al, ). However, prior vertebrate‐based selective forces for masting evolution cannot be ruled out (Janzen, , ; Waller, ).…”

High degree of polyphagy in a seed-eating bark beetle, <i>Coccotrypes gedeanus</i> (Coleoptera: Curculionidae: Scolytinae), during a community-wide fruiting event in a Bornean tropical rainforest

“…It is reasonable to infer that the high degree of polyphagy in C. gedeanus is adaptive for its survival in the Bornean tropical rain forests, where the density of each plant species is low and most of the plants produce fruit at unpredictably long intervals (Beaver 1979b, Novotny & Basset 2005. In addition, polyphagy helps to maintain the relatively abundant population of this bark beetle species in the assemblage of insect seed predators (Iku et al 2017(Iku et al , 2018.…”

Insect assemblages attacking seeds and fruits in a rainforest in Thailand

“…This is because it is difficult to survey the extremely diverse range of potential host plants with adequate spatial and temporal sampling effort, particularly with regard to predispersal seed predation (Ctvrtecka et al ). To the best of our knowledge, there are currently only six such examples that are relatively comprehensive: (i) Janzen's studies of insect seed predation in Guanacaste (targeting beetles and summarized in Janzen ) led to the formulation of the Janzen–Connell hypothesis, explaining the coexistence of tree species in tropical forests as resulting from negative density‐dependence processes (Janzen ); (ii) Nakagawa, Hosaka and their colleagues have studied insect seed predation in dipterocarp forests at two locations in Malaysia (Nakagawa et al , ; Hosaka et al , ; Iku et al ); (iii) Copeland et al () made a broad survey of insects feeding on wild fruits in Kenya, targeting tephritids; (iv) Ramírez and Traveset () published a comprehensive survey of insect seed predators in different habitats in Venezuela, including discontinuous patches of forest; (v) Ctvrtecka and colleagues studied insects feeding on both seeds and fruits with high sampling effort in a lowland forest of Papua New Guinea (Ctvrtecka et al , ; Sam et al ); and (vi) more recently, Gripenberg et al (, unpubl. data) undertook a similar survey on Barro Colorado Island in Panama.…”