Plant-animal interactions: patterns and mechanisms in terrestrial ecosystems

Bold rats (Niviventer confucianus) are more effective in seed dispersal: evidence both under enclosure conditions and in the field

Rodents are important seed dispersers of plants because they move seeds far away from the parent trees and hoard seeds in the soil, benefiting seed dispersal and regeneration. Traits of plant seeds and animals are associated with rodent-mediated seed dispersal, but animal personality, the consistent individual behavioral differences in time and environments, has not been fully considered. Here, we first measured the personality of 26 Niviventer confucianus in the laboratory, and 10 individuals in the field of one population, and then tested their behavior of seed consumption and hoarding both in semi-natural enclosures and the field. We tested the hypothesis that individuals with different personalities have different preferences for seed consumption and hoarding, which has different implications for seed dispersal and regeneration. Under the enclosure conditions, all parameters of personality are repeatable; bold individuals harvested fewer seeds but scatter-hoarded more seeds and dispersed farther than timid ones, whereas active individuals consumed more seeds, but left fewer seeds on the ground surface than inactive ones. In the field, boldness, activity, and exploration of the animals are repeatable; bold individuals scatter-hoarded more seeds to farther distances than timid ones, whereas active individuals harvested and consumed more seeds than inactive ones. These results suggest that bold rats tended to scatter hoard seeds and disperse them to a longer distance, implying they are more effective in seed dispersal. In the future, animal personality (e.g. boldness and activity) should be considered in seed dispersal studies and ecological-based manipulation in seed dispersal and regeneration of forests.

Asymmetric competition for seeds between two sympatric food hoarding rodents: implications for coexistence

Asymmetric competition occurs when some species have distinct advantages over their competitors and is common in animals with overlapping habitats and diet. However, the mechanism allowing coexistence between asymmetric competitors is not fully clear. Chinese white-bellied rats (Niviventer confucianus, CWR) and Korean field mice (Apodemus peninsulae, KFM) are common asymmetric competitors in shrublands and forests west of Beijing city. They share similar diet (e.g. plant seeds) and activity (nocturnal), but differ in body size (CWR are bigger than KFM), food hoarding habit (CWR: mainly larder hoarding; KFM: both larder and scatter hoarding), and ability to protect cached food (CWR are more aggressive than KFM). Here, we tested seed competition in 15 CWR-KFM pairs over a 10-day period under semi-natural enclosure conditions to uncover the differences in food hoarding, cache pilferage, and food protection between the 2 rodents, and discuss the implication for coexistence. Prior to pilferage, CWR harvested and ate more seeds than KFM. CWR tended to larder hoard seeds, whereas KFM preferred to scatter hoard seeds. Following pilferage, CWR increased consumption, decreased intensity of hoarding, and pilfered more caches from KFM than they lost, while KFM increased consumption more than they hoarded, and they preferred to hoard seeds in low and medium competition areas. Accordingly, both of the 2 rodent species increased their total energy consumption and hoarding following pilferage. Both rodent species tended to harvest seeds from the source, rather than pilfer caches from each other to compensate for cache loss via pilferage. Compared to CWR, KFM consumed fewer seeds when considering seed number, but hoarded more seeds when considering the seeds' relative energy (energy of hoarded seeds/rodent body mass2/3 ) at the end of the trials. These results suggest that asymmetric competition for food exists between CWR and KFM, but differentiation in hoarding behavior could help the subordinate species (i.e. KFM) hoard more energy than the dominant species (i.e. CWR), and may contribute to their coexistence in the field.

Nondormant Acorns Show Higher Seed Dispersal Effectiveness Than Dormant Ones

Seed dormancy has been thought to be an important survival strategy to tune the seed dispersal timing. Although a theoretical trade-off between seed dormancy and dispersal is often proposed, empirical field evidence of the trade-off between seed dormancy, spatial dispersal, and seedling recruitment is still lacking. Here, we tracked seed dispersal of several Fagaceae species exhibiting different levels of dormancy both in artificial enclosures and in the field. We presented evidence that oak species with nondormant acorns rather than those bearing dormant species exhibit reduced spatial dispersal. Despite the empirical evidence that seed germination is negatively correlated with spatial dispersal, nondormancy rather than dormancy showed higher seed dispersal effectiveness, demonstrating a negative correlation between seed dormancy and dispersal fitness. Our study, using the oak-rodent system, may provide solid evidence of a dispersal–germination trade-off between spatial and temporal correlation, highlighting the ecological role of seed germination schedule in seed dispersal and life-history evolution.

Tracking Animal-Dispersed Seedlings Using 15N Xylem Injection Method

Although various seed-marking methods have been developed for seed dispersal, it remains difficult to track the actual patterns of seed dispersal and seedling recruitment. Thus, new labeling methods that accurately track seedling establishment along with seed movement would help us better understand seed dispersal. Here, we developed a new nondestructive method using ¹⁵N xylem injection to track seed dispersal and seedling recruitment based on the enriched isotopic signals in the mature seeds. Our results first showed that xylem injection of ¹⁵N successfully enriched ¹⁵N both in the acorns and seedlings of Quercus variabilis. By marking acorns and seedlings with ¹⁵N stable isotopes, we successfully tracked seedlings established from acorns dispersed by seed-eating animals in the field. Our xylem ¹⁵N injection caused little alteration to seeds and showed no significant effects on seed selection by seed-eating animals as well as seed germination and seedling establishment, verifying the validity of the ¹⁵N xylem injection method to track seedling establishment. Our xylem ¹⁵N injection method is expected to be a powerful tool for tracking seed dispersal and seedling recruitment mediated by seed-eating animals in seed dispersal ecology.

Mutualism between antagonists: its ecological and evolutionary implications

Mutualism or antagonism between species is often investigated within the framework of monotonic interactions of either mutualism or antagonism, but studies on transition from mutualism to antagonism (within the context of nonmonotonic interactions) have been largely ignored. In this paper, through a brief review and synthesis, we highlighted the role of mutualism between antagonists in regulating the ecological and evolutionary processes, as well as maintaining the stability and complexity of ecosystems. Mutualism between antagonistic species represents the density-dependent transition between mutualism and antagonism, which is beneficial to species coexistence and stability of complex ecosystems; thus, it should be favored by natural selection. Species may face selection of conflicting pressure on functional traits in co-balancing mutualism and antagonism, which may result in evolution of the dual character of species with moderate mutualistic or antagonistic traits. Coevolution and co-balance of these traits are driving forces in shaping mutualism-antagonism systems. Rewards for mutualists, punishment for exploiters, and competition of meta-communities are essential in stabilizing mutualism between antagonists. We appeal for more studies on mutualism between antagonists and its ecological and evolutionary implications by expanding the conventional ecological studies from monotonic to nonmonotonic regimes.

Compared with conventional PCR assay, qPCR assay greatly improves the detection efficiency of predation

Studies of predation can contribute greatly to understanding predator-prey relationships and can also provide integral knowledge concerning food webs and multi-trophic level interactions. Both conventional polymerase chain reaction (cPCR) and quantitative PCR (qPCR) have been employed to detect predation in the field because of their sensitivity and reproducibility. However, to date, few studies have been used to comprehensively demonstrate which method is more sensitive and reproducible in studies of predation. We used a Drosophila melanogaster-specific DNA fragment (99 bp) to construct a tenfold gradient dilution of standards. Additionally, we obtained DNA samples from Pardosa pseudoannulata individuals that fed on D. melanogaster at various time since feeding. Finally, we compared the sensitivity and reproducibility between cPCR and qPCR assays for detecting DNA samples from feeding trials and standards. The results showed that the cPCR and qPCR assays could detect as few as 1.62 × 103 and 1.62 × 101 copies of the target DNA fragment, respectively. The cPCR assay could detect as few as 48 hr post-feeding of the target DNA fragment. But the qPCR assay showed that all spiders were positive after consuming prey at various time intervals (0, 24, 48, 72, and 96 hr). A smaller proportion of the technical replicates were positive using cPCR, and some bands on the agarose gel were absent or gray, while some were white and bright for the same DNA samples after amplification by cPCR. By contrast, a larger proportion of the technical replicates were positive using qPCR and the coefficients of variation of the Ct value for the three technical replicates of each DNA sample were less than 5%. These data showed that qPCR was more sensitive and highly reproducible in detecting such degraded DNA from predator's gut. The present study provides an example of the use of cPCR and qPCR to detect the target DNA fragment of prey remains in predator's gut.

Plant-animal interactions between carnivorous plants, sheet-web spiders, and ground-running spiders as guild predators in a wet meadow community

Plant-animal interactions are diverse and widespread shaping ecology, evolution, and biodiversity of most ecological communities. Carnivorous plants are unusual in that they can be simultaneously engaged with animals in multiple mutualistic and antagonistic interactions including reversed plant-animal interactions where they are the predator. Competition with animals is a potential antagonistic plant-animal interaction unique to carnivorous plants when they and animal predators consume the same prey.The goal of this field study was to test the hypothesis that under natural conditions, sundews and spiders are predators consuming the same prey thus creating an environment where interkingdom competition can occur.Over 12 months, we collected data on 15 dates in the only protected Highland Rim Wet Meadow Ecosystem in Kentucky where sundews, sheet-web spiders, and ground-running spiders co-exist. One each sampling day, we attempted to locate fifteen sites with: (a) both sheet-web spiders and sundews; (b) sundews only; and (c) where neither occurred. Sticky traps were set at each of these sites to determine prey (springtails) activity-density. Ground-running spiders were collected on sampling days. DNA extraction was performed on all spiders to determine which individuals had eaten springtails and comparing this to the density of sundews where the spiders were captured.Sundews and spiders consumed springtails. Springtail activity-densities were lower, the higher the density of sundews. Both sheet-web and ground-running spiders were found less often where sundew densities were high. Sheet-web size was smaller where sundew densities were high.The results of this study suggest that asymmetrical exploitative competition occurs between sundews and spiders. Sundews appear to have a greater negative impact on spiders, where spiders probably have little impact on sundews. In this example of interkingdom competition where the asymmetry should be most extreme, amensalism where one competitor experiences no cost of interaction may be occurring.

Exclusion of interspecific competition reduces scatter-hoarding of Siberian chipmunk Tamias sibiricus: A field study

Although food availability and the abundance of seed predators have been postulated to affect seed dispersal, it is not clear how seed-eating animals modify their scatter-hoarding strategies in response to different levels of interspecific competition. We placed paired germinated and ungerminated acorns of Quercus mongolica on 30-cm high platforms to exclude potential interspecific competition of the predominant larder hoarders Apodemus peninsulae and Myodes rufocanus, to investigate seed dispersal by a predominant scatter-hoarder, Tamias sibiricus, in the field in north-eastern China. Our results showed that T. sibiricus ate more acorns in situ in the absence of interspecific competition. In the presence of interspecific competition of A. peninsulae and C. rufocanus, however, more acorns were scatter-hoarded by T. sibiricus. Regardless of interspecific competition, germination of acorns showed no significant effects on seed dispersal patterns, inconsistent with the "seed perishability hypothesis" that animals avoid hoarding seeds with high perishability. Exclusion of interspecific competition, though relatively increasing the per capita seed abundance, appears to reduce seed dispersal, scatter-hoarding and seedling establishment. Therefore, we propose that moderate interspecific competition rather than competition exclusion may benefit seed scatter-hoarding and seedling establishment.