| Seed dispersal is one of the most important ecological processes.Dispersal by animals is a ubiquitous mode of seed dispersal in almost all terrestrial ecosystems.Although literatures on the seed dispersal by vertebrates(e.g.birds and mammals)are vast,there are relatively few studies on the ant-mediated seed dispersal.Seed dispersal by ants(i.e.myrmecochory)is a widespread and important ecological interaction in which ants benefit by gaining nutrition from lipid-rich elaiosomes attached to seeds.Plants benefit from having their seeds dispersed away from parent plants.The purpose of this study is to investigate the effects of ant behaviors(behavior of foraging and re-dispersal),plant traits(plant volatiles),and biotic factor(seed neighbouring effects)on seed dispersal,and investigate the response of ants to human-altered habitats.The conclusions are as follows:(1)Pristomyrmex pungens and Prenolepis sphingthorax were the main seed dispersers of the Corydalis seeds in the study sites.The former could recruit a large number of ants to remove seeds(mass recruitment mode),while the latter could recruit 5-30 ants to remove seeds(simple cooperative recruitmen mode).P.pungens carried about 44%of the C.wilfordii seeds transported by it to the nests,with the average dispersal distance of 1.85 m and the removal number of seeds per hour of 43.8,while the elaiosome of the rest seeds were removed in situ and/or on the way to the nest.P.sphingthorax carried all C.wilfordii seeds to the nests,with the average dispersal distance of 0.45 m and the removal number of seeds per hour of 7.3.In addition,both ants could carry the all C.racemosa seeds to the nests,with the average dispersal distance of 6.27 m and 6.65 m,and removal number of seeds per hour of 34.2 and 10.6 respectively.The results suggested that seed removal rate by ant with mass recruitment was higher than that by ant with simple cooperative recruitment.The dispersal distance and short-term seed fate differed between the two Corydalis plants,depending on ant foraging strategies and behavior and seed characteristics.(2)We compared the consequences of seed re-dispersal by a keystone seed-dispersing ant(Myrmica ruginodis)for four sympatric myrmecochorous plants.Plants varied in the probability of re-dispersal and in elaiosome condition.Ants preferred seeds with residual elaiosomes,while rodents only consumed the two larger-seeded species,regardless of the elaiosome presence.The scattered distribution of discarded seeds increased the probability of ant re-harvesting and,to some extent,reduced rodent predation.Thus,difference in the probability of seed re-dispersal and its subsequent effect on seed fate in relation to ants and rodents was attributed primarily to the elaiosome condition,seed size and seed spatial pattern.The results imply that seed re-dispersal could affect the fitness of plants and ultimately influence the plant abundance and distribution pattern.This highlights the necessity to incorporate re-dispersal into myrmecochory to advance our understanding of the benefits of myrmecochory to plants.(3)We investigated the difference between two common Chinese mrrmecochorous plants,C.incisa and C.wilfordii,in the importance of each dispersal step by examining 1)primary dispersal distance,2)seed removal rates and dispersal distance by ants,and 3)frequency of seeds discarded out of nests and the re-dispersal distance.We found that the mean primary dispersal distance of C.incisa was about eight times longer than that of C.wilfordii.The presence of an elaiosome increase the attractiveness of seeds to ants,and both the removal rate and dispersal distance were greater in C.wilfordii than in C.incisa.Two ant species,Pheidole noda and Pristomyrmex pungens are the major dispersers.Pheidole.noda,the larger-bodied ant species,discarded most seeds of both species out of nests,whereas P.pungens discarded only C.wilfordii seeds.The mean re-dispersal distances of the two species were similar,but that of C.incisa and C.wilfordii were about threefold and fivefold shorter than the distances in the step of ant dispersal,respectively.In the field,no predators were found to interact with the discarded seeds in 72 h.Our results indicate that the importance of each dispersal phase differ between the two Corydalis species,and this difference is largely attributable to the differential role of ant identity and seed characteristics.It is concluded that re-dispersal also needs to be considered in studies of myrmecochory.(4)It has been reported that a suit of plant traits can mediate the ant-seed interaction and subsequently affect the seed dispersal.However,the functional role of plant volatiles relating to ant-mediated seed dispersal remain little examined.We used a Y-tube olfactometer to test behavior response of a keystone seed-dispersing ant(P.pungens)to leaves and seeds of five co-occurring myrmecochorous Corydalis species(C.wilfordii,C.racemosa,C.sheareri,C.balansae and C.incisa).Of the five species,only C.wilfordii and C.racemosa organs emits heavily volatiles.We also performed seed cafeteria experiments to assess the effect of leaf volatiles from C.racemosa on seed retrieval by presenting simultaneously the seeds near the fresh leaf and the leaf immersed by diethyl ether both in the field and lab.The experiment using Y-tube showed that the ants were only significantly attracted by the fresh leaves of two species,C.wilfordii and C.racemosa.The cafeteria experiments showed that ants spent less time to detect the C.racemosa seeds which near the fresh leaf,and transported these seeds more quickly.This indicated that the leaf volatiles can function as an attractant for the dispersing ants,and ant' preference in turn enhance the seed retrieval.The finding reveals that leaf volatiles may play an important but underestimated role in shaping the ant-seed dispersing interactions.(5)We investigated the influences of neighboring seeds on seed removal in two coexisting myrmecochorous species(E.pubescens and H.thibetanus)from temperate deciduous forests of Qinling Mountains,central China,and examined the potential role of ants and rodents by exclusion experiments(ant exclusion,rodent exclusion and full access).We also examined whether the seeds neighboring effects differ between forest edge and interior.We found that,in both ant exclusion(rodent alone)and full access(rodents + ants),the presence of neighboring seeds did nota affect removal of focal seeds in forest edge and interior.Whereas in rodent exclusion(ant alone),the presence of lower-ESMR(elaiosome:seed mass ratio)H.thibetanus significantly decreased the removal rates of higher-ESMR E.pubescens,which was only observed in forest interior.The keystone seed-dispersing ant,M.ruginodis is more abundant in forest edge compared to interior.The result indicates that neighboring seeds can greatly influence the seed removal of focal plants by ants in absence of rodents,while the seed neighborhood effects disappear when the rodents present.The neighborhood effect also disappears in forest edge,probably due to the greater abundance of keystone seed-dispersing ants in that habitat than forest interior.The findings would contribute to a better understanding of the coexistence and maintenance of diverse ant-dispersed herbs in temperature forests.(6)We investigated the effect of disturbance on the abundance,richness,and composition of ant communities and the resulting seed-dispersal services for a herbaceous myrmecochore,Corydalis giraldii(Papaveraceae),in an undisturbed habitat(forest understory),moderately disturbed habitat(abandoned farm field),and highly disturbed habitat(road verge)on Qinling Mountains,China In total,we recorded 13 ant species,and five out of these were observed to transport seeds.The community composition of dispersers was significantly different amongst habitats.The richness of the dispersers did not differ among the habitats,but their total abundance significantly varied across habitats and was recorded to decrease in the road verge by 21%,in comparison to abandoned farm fields.The major seed-dispersing ant species in both the forest understory and abandoned farm field were large-bodied(Myrmica sp.and Formica fusca,respectively),whereas the major seed-dispersing ants found in the road verge were small-bodied(Lasius alienus).This difference resulted in lower seed removal rates and dispersal distances in the road verge than in the other two habitats.The different dispersal patterns were attributed primarily to differences in dispersing ant abundance and identity,most likely in response to habitats with different degree of anthropogenic disturbance.The possible influence of disturbance on the ecological specialization of ant-seed dispersal interaction was also discussed.These results indicated that bebavior of ant foraging and re-dispersal affected the seed removal rates and seed fate;leaf volatiles from some Corydalis species promote the seed dispersal by ants;the presence of neighborhood seeds and the habitat disturbance can affect the ant abundance,richness and ant foraging behavior,and therefore the interaction between ants and plants. |
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