Passive directed dispersal of plants by animals

Functional connectivity of animal-dispersed plant communities depends on the interacting effects of network specialization and resource diversity

Plant functional connectivity-the dispersal of plant propagules between habitat patches-is often ensured through animal movement. Yet, there is no quantitative framework to analyse how plant-animal interactions and the movement of seed dispersers influence community-level plant functional connectivity. We propose a trait-based framework to quantify plant connectivity with a model integrating plant-frugivore networks, animal-mediated seed-dispersal distances and the selection of target patches by seed dispersers. Using this framework, we estimated how network specialization, between-patch distance and resource diversity in a target patch affect the number and diversity of seeds dispersed to that patch. Specialized networks with a high degree of niche partitioning in plant-frugivore interactions reduced functional connectivity by limiting the diversity of seeds dispersed over long distances. Resource diversity in the target patch increased both seed number and diversity, especially in specialized networks and within short and intermediate distances between patches. Notably, resource diversity was particularly important at intermediate distances, where the number and diversity of seeds reaching a patch increased more strongly with resource diversity than at longer distances. Using a trait-based framework, we show that resource diversity in the target patch is a major driver of connectivity in animal-dispersed plant communities.

Partitioning the Impacts of Spatial-Temporal Variation in Demography and Dispersal on Metapopulation Growth Rates

AbstractSpatial-temporal variation in environmental conditions is ubiquitous in nature. This variation simultaneously impacts survival, reproduction, and movement of individuals and thereby the rate at which metapopulations grow. Using the tools of stochastic demography, the metapopulation growth rate is decomposed into five components corresponding to temporal, spatial, and spatial-temporal variation in fitness and spatial and spatial-temporal covariation in dispersal and fitness. While temporal variation in fitness always reduces the metapopulation growth rate, all other sources of variation can either increase or reduce the metapopulation growth rate. Increases occur either by reducing the impacts of temporal variation or by generating a positive fitness-density covariance where individuals tend to concentrate in higher-quality patches. For example, positive autocorrelations in spatial-temporal variability in fitness generate this positive fitness-density covariance for less dispersive populations but decrease it for highly dispersive populations (e.g., migratory species). Negative autocorrelations in spatial-temporal variability have the opposite effects. Positive covariances between movement and future fitness, on short or long timescales, increase growth rates. These positive covariances can arise in unexpected ways. For example, the win-stay, lose-shift dispersal strategy in negatively autocorrelated environments can generate positive spatial covariances that exceed negative spatial-temporal covariances. This decomposition of the metapopulation growth rate provides a way to quantify the relative importance of fundamental sources of variation for metapopulation persistence.

Harder, better, faster, stronger? Dispersal in the Anthropocene

The dispersal of organisms in the Anthropocene has been profoundly altered by human activities, with far-reaching consequences for humans, biodiversity, and ecosystems. Managing such dispersal effectively is critical to achieve the 2030 targets of the Kunming-Montreal Global Biodiversity Framework. Here, we bring together insights from invasion science, movement ecology, and conservation biology, and extend a widely used classification framework for the introduction pathways of alien species to encompass other forms of dispersal. We develop a simple, global scheme for classifying the movement of organisms into the types of dispersal that characterise the Anthropocene. The scheme can be used to improve our understanding of dispersal, provide policy relevant advice, inform conservation and biosecurity actions, and enable monitoring and reporting towards conservation targets.

Substrate scent-induced disproportionate seed dispersal by rodents

Conspecific adults impose strong negative density-dependent effects on seed survival nearby parent trees, however, the underlying mechanisms are diversified and remain unclear. In this study, we presented consistent evidence that parent-scented forest floor masked seed odor, reduced cache recovery rate by scatter-hoarding animals, and then increased seed dispersal far away from mother trees. Our results showed that seed odors of Korean pine Pinus koraiensis match well with the volatile profile of their forest floor. Moreover, scatter-hoarding animals selectively transported P. koraiensis seeds toward the areas where seed odor was more contrasting against the background substrate, possibly due to the fact that accumulation of conspecific volatile compounds in caches hindered seed detection by scatter-hoarding animals. Our study provides insight into the role of leaf litter in directing seed dispersal process, representing a novel mechanism by which P. koraiensis increases selection for seed dispersal far away from the parent tree.

Multifunctionality of angiosperm floral bracts: a review

Floral bracts (bracteoles, cataphylls) are leaf-like organs that subtend flowers or inflorescences but are of non-floral origin; they occur in a wide diversity of species, representing multiple independent origins, and exhibit great variation in form and function. Although much attention has been paid to bracts over the past 150 years, our understanding of their adaptive significance remains remarkably incomplete. This is because most studies of bract function and evolution focus on only one or a few selective factors. It is widely recognised that bracts experience selection mediated by pollinators, particularly for enhancing pollinator attraction through strong visual, olfactory, or echo-acoustic contrast with the background and through signalling the presence of pollinator rewards, either honestly (providing rewards for pollinators), or deceptively (attraction without reward or even trapping pollinators). However, studies in recent decades have demonstrated that bract evolution is also affected by agents other than pollinators. Bracts can protect flowers, fruits, or seeds from herbivores by displaying warning signals, camouflaging conspicuous reproductive organs, or by providing physical barriers or toxic chemicals. Reviews of published studies show that bracts can also promote seed dispersal and ameliorate the effects of abiotic stressors, such as low temperature, strong ultraviolet radiation, heavy rain, drought, and/or mechanical abrasion, on reproductive organs or for the plants' pollinators. In addition, green bracts and greening of colourful bracts after pollination promote photosynthetic activity, providing substantial carbon (photosynthates) for fruit or seed development, especially late in a plant's life cycle or season, when leaves have started to senesce. A further layer of complexity derives from the fact that the agents of selection driving the evolution of bracts vary between species and even between different developmental stages within a species, and selection by one agent can be reinforced or opposed by other agents. In summary, our survey of the literature reveals that bracts are multifunctional and subject to multiple agents of selection. To understand fully the functional and evolutionary significance of bracts, it is necessary to consider multiple selection agents throughout the life of the plant, using integrative approaches to data collection and analysis.

Exposing the error hidden in plain sight: A critique of Calder's (1983) group selectionist seed-dispersal hypothesis for mistletoe "mimicry" of host plants

Some mistletoe species (Loranthaceae) resemble their host plants to a striking degree. Various mechanisms have been proposed for the developmental origins of novel traits that cause mistletoes to appear similar to their hosts, as well as for the adaptive phenotypic evolution of such traits. Calder (1983) proposed a logically flawed group selectionist seed-dispersal hypothesis for mistletoes to resemble their hosts. Calder's (1983) hypothesis does not provide a viable potential explanation for mistletoe resemblance to hosts.

Animal-mediated plant niche tracking in a changing climate

Over half of plant species are animal-dispersed, and our understanding of how animals can help plants move in response to climate change - a process known as niche tracking - is limited, but advancing rapidly. Recent research efforts find evidence that animals are helping plants track their niches. They also identify key conditions needed for animal-mediated niche tracking to occur, including alignment of the timing of seed availability, the directionality of animal movements, and microhabitat conditions where seeds are deposited. A research framework that measures niche tracking effectiveness by considering all parts of the niche-tracking process, and links together data and models from multiple disciplines, will lead to further insight and inform actions to help ecosystems adapt to a changing world.

Influence of tree-fall gaps on directional seed dispersal by small mammals in Central Panama

Small mammals, particularly rodents, are often important seed-dispersal agents in Neotropical forests. Directional seed dispersal into tree-fall gaps may enhance seedling survival of light-demanding species and thus influence forest regeneration. To examine this proposition, we tracked seeds of a light-demanding palm (Attalea butyracea), with a focus on spiny rats (Proechimys semispinosus), the most-likely seed-removal agents. We established seed-removal stations at three distances relative to 28 gaps (gap center, gap edge, and intact forest 10 m from a gap edge) in a lowland forest in Central Panama. We placed five fresh fruits (with their seed) in semi-permeable exclosures to exclude larger mammals at each station and tracked the directions in which seeds were moved and deposited intact. More seeds were moved toward or into gaps when removed from gap center or edge stations; however, seeds dispersed from intact forest stations showed no such directionality. Small mammals may have dispersed seeds into and within tree-fall gaps because they favored caching seeds in areas that offered increased cover, which is typical of gaps, and consequently protection from predation. The lack of directional dispersal from intact forest stations may have been because spiny rats were able to find sufficient cover in the young intact forest that was closer than the gaps. In older forest, the contrast between intact forest and gaps may be greater, resulting in directed dispersal into gaps.