Habitat differences in dung beetle assemblages in an African savanna–forest ecotone:implications for secondary seed dispersal

The probability and pattern of secondary seed dispersal by dung beetles(Scarabaeinae)depend on their community structure and composition at the site of primary deposition,which,in turn,seem to be strongly determined by vegetation.Consequently,we expected pronounced differences in secondary seed dispersal between forest and savanna in the northern Ivory Coast,West Africa.We found 99 dung beetle species at experimentally exposed dung piles of the olive baboon(Papio anubis(Lesson,1827)),an important primary seed disperser in West Africa.Seventy-six species belonged to the roller and tunneler guilds,which are relevant for secondary seed dispersal.Most species showed a clear habitat preference.Contrary to the Neotropics,species number and abundance were much higher in the savanna than in the forest.Rollers and tunnelers each accounted for approximately 50%of the individuals in the savanna,but in the forest rollers made up only 4%.Seeds deposited into the savanna by an omnivorous primary disperser generally have a higher overall probability of being more rapidly dispersed secondarily by dung beetles than seeds in the forest.Also,rollers disperse seeds over larger distances.In contrast to other studies,small rollers were active in dispersal of large seeds,which were seemingly mistaken for dung balls.Our results suggest that rollers can remove seeds from any plant dispersed in primate dung in this ecosystem.

Trait-mediated seed predation, dispersal and survival among frugivore-dispersed plants in a fragmented subtropical forest, Southwest China

By tracking the fate of individual seeds from 6 frugivore-dispersed plants with contrasting seed traits in a frag­mented subtropical forest in Southwest China,we explored how rodent seed predation and hoarding were influ­enced by seed traits such as seed size,seed coat hardness and seed profitability.Post-dispersal seed fates var­ied significantly among the 6 seed species and 3 patterns were witnessed:large-seeded species with a hard seed coat(i.e.Choerospoadias axillaries and Diospyros kaki var.silvestris)had more seeds removed,cached and then surviving at caches,and they also had fewer seeds predated but a higher proportion of seeds surviving at the source;medium-sized species with higher profitability and thinner seed coat(i.e.Phoebe zhennan and Pa­dus braohypoda)were first harvested and had the lowest probability of seeds surviving either at the source or at caches due to higher predation before or after removal;and small-seeded species with lower profitability(i.e.Elaeocarpus japonicas and Cornus controversa)had the highest probability of seeds surviving at the source but the lowest probability of seeds surviving at caches due to lower predation at the source and lower hoarding at caches.Our study indicates that patterns of seed predation,dispersal and survival among frugivore-dispersed plants are highly determined by seed traits such as seed size,seed defense and seed profitability due to selective predation and hoarding by seed-eating rodents.Therefore,trait-mediated seed predation,dispersal and survival via seed-eating rodents can largely affect population and community dynamics of frugivore-dispersed plants in fragmented forests.

Seed handling by primary frugivores differentially influence post-dispersal seed removal of Chinese yew by ground-dwelling animals

Seed handling by primary frugivores can influence secondary dispersal and/or predation of post-dispersal seeds by attracting different guilds of ground-dwelling animals.Many studies have focused on seeds embedded in fe­ces of mammals or birds;however,less is known about how ground-dwelling animals treat seeds regurgitated by birds(without pulp and not embedded in feces).To compare the effect of differential seed handling by pri­mary dispersers on secondary seed removal of Chinese yew(Taxus chinensis var.mairei),we conducted a series of exclosure experiments to determine the relative impact of animals on the removal of defecated seeds(handled by masked palm civet),regurgitated seeds(handled by birds)and intact fruits.All types of yew seeds were con­sistently removed at a higher rate by rodents than by ants.Regurgitated seeds had the highest removal percent­age and were only removed by rodents.These seeds were probably eaten in situ without being secondarily dis­persed.Defecated seeds were removed by both rodents and ants;only ants might act as secondary dispersers of defecated seeds,whereas rodents ate most of them.We inferred that seeds regurgitated by birds were subject­ed to the highest rates of predation,whereas those dispersed in the feces of masked palm civets probably had a higher likelihood of secondary dispersal.Seeds from feces attracted ants,which were likely to transport seeds and potentially provided a means by which the seeds could escape predation by rodents.Our study highlighted that primary dispersal by birds might not always facilitate secondary dispersal and establishment of plant popu­lations.

Predation of cassowary dispersed seeds:is the cassowary an effective disperser?

Post-dispersal predation is a potentially significant modifier of the distribution of recruiting plants and an often unmeasured determinant of the effectiveness of a frugivore’s dispersal service.In the wet tropical forests of Austra-lia and New Guinea,the cassowary provides a large volume,long distance dispersal service incorporating benefi-cial gut processing;however,the resultant clumped deposition might expose seeds to elevated mortality.We exam-ined the contribution of post-dispersal seed predation to cassowary dispersal effectiveness by monitoring the fate of 11 species in southern cassowary(Casuarius casuarius johnsonii Linnaeus)droppings over a period of 1 year.Across all species,the rate of predation and removal was relatively slow.After 1 month,70%of seeds remained intact and outwardly viable,while the number fell to 38%after 1 year.The proportion of seeds remaining intact in droppings varied considerably between species:soft-seeded and large-seeded species were more likely to escape removal and predation.Importantly,across all species,seeds in droppings were no more likely to be predated than those left undispersed under the parent tree.We speculate that seed predating and scatter-hoarding rodents are responsible for the vast majority of predation and removal from droppings and that the few seeds which undergo secondary dispersal survive to germination.Our findings reinforce the conclusion that the cassowary is an impor-tant seed disperser;however,dispersal effectiveness for particular plant species can be reduced by massive post-dispersal seed mortality.