Fungi and insects compensate for lost vertebrate seed predation in an experimentally defaunated tropical forest

Abstract

Overhunting reduces important plant-animal interactions such as vertebrate seed dispersal and seed predation, thereby altering plant regeneration and even above-ground biomass. It remains unclear, however, if non-hunted species can compensate for lost vertebrates in defaunated ecosystems. We use a nested exclusion experiment to isolate the effects of different seed enemies in a Bornean rainforest. In four of five tree species, vertebrates kill many seeds (13–66%). Nonetheless, when large mammals are excluded, seed mortality from insects and fungi fully compensates for the lost vertebrate predation, such that defaunation has no effect on seedling establishment. The switch from seed predation by generalist vertebrates to specialist insects and fungi in defaunated systems may alter Janzen–Connell effects and density-dependence in plants. Previous work using simulation models to explore how lost seed dispersal will affect tree species composition and carbon storage may require reevaluation in the context of functional redundancy within complex species interactions networks.

Weak effects of birds, bats, and ants on their arthropod prey on pioneering tropical forest gap vegetation

“…However, observable (but not significant) positive LRR of woody plant biomass were not coupled with any detectable differences in density nor diversity between control and exclosure plots (Szefer et al, 2020). This suggests that negative effects of small rodents were weak or, more probably, compensated by increased pressure of herbivorous insects (Williams et al, 2021). Nevertheless, interactive effects of small rodent and insect predator exclusion should not be ignored in further exclosure studies.…”

“…Competitive interactions among plants are generally assumed to be the key force that structures early successional vegetation (Vel azquez & Wiegand, 2020). This assumption differs from our concepts for the closed canopy forests where biotic factors, for example, mammals, herbivorous insects, and pathogenic fungi have been shown to strongly affect community assembly process in mature tropical forest habitats (Bagchi et al, 2014;Blackham & Corlett, 2015;Jia et al, 2018;Williams et al, 2021).…”

Direct comparisons of logging and agroforestry influence on tropical mammals in Sarawak, Borneo

“…Likewise, we also detected leopard cats at a higher frequency in unlogged forest, whereas this species is often detected more frequently in disturbed forest (Mohamed et al, 2013;Mohamed et al, 2016). The occurrence of other mammal these species may affect forest regeneration via seed predation and seed dispersal (Brodie et al, 2009;Granados et al, 2017;Williams et al, 2021); if the species remain in logged forest and agroforestry, such ecosystem processes may remain viable.…”

“…Species such as bearded pig, binturong ( Arctictis binturong ), Malayan porcupine, long‐tailed porcupine, Malay civet, short‐tailed mongoose ( Urva brachyura ), Sunda pangolin ( Manis javanica ), yellow muntjac ( Muntiacus atherodes ), and yellow‐throated marten ( Martes flavigula ) were found in all habitat types, suggesting that these species are habitat generalists that are less vulnerable to habitat disturbance. Some of these species may affect forest regeneration via seed predation and seed dispersal (Brodie et al, 2009; Granados et al, 2017; Williams et al, 2021); if the species remain in logged forest and agroforestry, such ecosystem processes may remain viable.…”

Small mammals reduce distance dependence and increase seed predation risk in tropical rainforest fragments

“…Previous experiments in contiguous forests suggest that insects can offset reductions in seed predation brought about by the loss or exclusion of mammals (Williams et al, 2021;Wright & Duber, 2001).…”