Temporal Variation In Dispersal Research Articles

Ecological and evolutionary consequences of temporal variation in dispersal

The importance of dispersal rates and distances has long been appreciated by ecologists and evolutionary biologists. An emerging field of research is revealing how temporal variation in dispersal can substantially influence ecological and evolutionary outcomes. We review how dispersal rates can temporally vary substantially in many ecosystems, a pattern that is particularly well‐documented for aquatic organisms but is likely pervasive in terrestrial ecosystems as well. We then synthesize the effects of temporal variation in dispersal on five key ecological and evolutionary processes: 1) metapopulation dynamics, 2) local adaptation, 3) range limits and range expansions, 4) species coexistence and 5) metacommunity dynamics. Our review demonstrates that temporal variation in dispersal is more than just statistical ‘noise' but can in fact lead to different outcomes than expected were dispersal temporally constant. For example, increasing the magnitude of temporal variation in dispersal can lead to lower metapopulation growth rates, permit greater local adaptation, facilitate and accelerate range expansion, increase regional coexistence, and alter local and regional species diversity. These effects of temporal variation in dispersal can inform conservation and natural resource management decisions such as prioritization in spatial planning, management of spillover from domesticated or captive populations into native populations, and the design of effective control strategies for invasive species.

Quantifying dispersal variability among nearshore marine populations.

Dispersal drives diverse processes from population persistence to community dynamics. However, the amount of temporal variation in dispersal and its consequences for metapopulation dynamics is largely unknown for organisms with environmentally driven dispersal (e.g., many marine larvae, arthropods and plant seeds). Here, we used genetic parentage analysis to detect larval dispersal events in a common coral reef fish, Amphiprion clarkii, along 30km of coastline consisting of 19 reef patches in Ormoc Bay, Leyte, Philippines. We quantified variation in the dispersal kernel across seven years (2012-2018) and monsoon seasons with 71 parentage assignments from 791 recruits and 1,729 adults. Connectivity patterns differed significantly among years and seasons in the scale and shape but not in the direction of dispersal. This interannual variation in dispersal kernels introduced positive temporal covariance among dispersal routes that theory predicts is likely to reduce stochastic metapopulation growth rates below the growth rates expected from only a single or a time-averaged connectivity estimate. The extent of variation in mean dispersal distance observed here among years is comparable in magnitude to the differences across reef fish species. Considering dispersal variation will be an important avenue for further metapopulation and metacommunity research across diverse taxa.

Geographic variation in dispersal distance facilitates range expansion of a lake shore plant in response to climate change

AbstractAimGeographic variation in dispersal abilities is widespread and likely to affect species' range dynamics in response to climate change. However, distribution models that predict climate‐induced range shifts do not account for spatial variation in dispersal. We developed an eco‐genetic model to investigate how variation in dispersal distances across a species' range could interact with climate‐induced selection and alter predicted range dynamics in a species with documented variation in dispersal traits.LocationWe investigated the range of an annual plant, Cakile edentula var. lacustris, which occupies beaches spanning a 555 km latitudinal gradient along the Laurentian Great Lakes.MethodsWe built a hybrid model that combines climatic niche modelling, based on decadal climate projections, with an individual‐based model that allows for evolutionary processes to act upon a heritable dispersal kernel. We evaluated how spatial variation in dispersal distance and dispersal evolution influenced range dynamics, spatial and temporal variation in dispersal, and the distribution of neutral genetic variation. The model was parametrized with data on C. edentula's distribution, life history and dispersal characteristics.ResultsGeographic variation in dispersal distance, adaptive dispersal evolution and dispersal distance increased the potential for local populations of C. edentula to keep pace with changing climatic conditions through range shifts. Dispersal distances always increased at the expanding and contracting range edges when dispersal was allowed to evolve. Furthermore, scenarios where dispersal distances were initially lower at the range edges resulted in the largest evolutionary changes over 105 years (>1.5 km increase in mean distance at northern edge). Adaptive dispersal evolution always reduced neutral genetic diversity across the species' range.Main conclusionsVariation in dispersal abilities across C. edentula's range and adaptive evolution led to different predicted outcomes in range dynamics during climate change illustrating the importance of including spatial variation in dispersal into species distribution models.

Temporal variation in dispersal modifies dispersal-diversity relationships in an experimental seagrass metacommunity

Temporal variation in dispersal modifies dispersal-diversity relationships in an experimental seagrass metacommunity

Can we predict the expansion rate of a translocated butterfly population based on a priori estimated movement rates?

Conservation translocation is a controversial, yet sometimes the only applicable, conservation tool in the face of the human-induced environmental change. One important aspect often neglected in translocation experiments is predicting the spatial expansion potential of the translocated population in the release area. In this study, we used a spatially explicit movement model to project the expansion rate of a translocated clouded Apollo (Parnassius mnemosyne) population. The model was parameterised with data collected from the source population inhabiting an open landscape with well-connected habitat patches. We then used these parameter estimates to simulate the spread of the translocated population in the new area, which was a forested landscape with more fragmented habitat. We tested the model predictions by comparing them to the observed expansion rate between 2000 and 2016. Additionally, we tested whether including annually varying weather conditions would increase realism in the projections. Model predictions were qualitatively correct and quantitatively most accurate for flight seasons with prevailing weather conditions similar to those of the season when the data for parameter estimation was collected. We conclude that spatially explicit movement models are potential tools to improve the planning of future conservation translocations in terms of choosing the optimal release area, as they enable the comparison of functional connectivities even between structurally different landscapes. However, our results suggest that a model fitted based on movement data from a single year may not be representative for the overall dispersal rates due to temporal variation in dispersal.

Anticipating changes to future connectivity within a network of marine protected areas.

Continental boundary currents are projected to be altered under future scenarios of climate change. As these currents often influence dispersal and connectivity among populations of many marine organisms, changes to boundary currents may have dramatic implications for population persistence. Networks of marine protected areas (MPAs) often aim to maintain connectivity, but anticipation of the scale and extent of climatic impacts on connectivity are required to achieve this critical conservation goal in a future of climate change. For two key marine species (kelp and sea urchins), we use oceanographic modelling to predict how continental boundary currents are likely to change connectivity among a network of MPAs spanning over 1000km of coastline off the coast of eastern Australia. Overall change in predicted connectivity among pairs of MPAs within the network did not change significantly over and above temporal variation within climatic scenarios, highlighting the need for future studies to incorporate temporal variation in dispersal to robustly anticipate likely change. However, the intricacies of connectivity between different pairs of MPAs were noteworthy. For kelp, poleward connectivity among pairs of MPAs tended to increase in the future, whereas equatorward connectivity tended to decrease. In contrast, for sea urchins, connectivity among pairs of MPAs generally decreased in both directions. Self-seeding within higher-latitude MPAs tended to increase, and the role of low-latitude MPAs as a sink for urchins changed significantly in contrasting ways. These projected changes have the potential to alter important genetic parameters with implications for adaptation and ecosystem vulnerability to climate change. Considering such changes, in the context of managing and designing MPA networks, may ensure that conservation goals are achieved into the future.

Similarity in temporal variation in sex-biased dispersal over short and long distances in the dark-eyed junco, Junco hyemalis.

Patterns of sex-biased dispersal (SBD) are typically consistent within taxa, for example female-biased in birds and male-biased in mammals, leading to theories about the evolutionary pressures that lead to SBD. However, generalizations about the evolution of sex biases tend to overlook that dispersal is mediated by ecological factors that vary over time. We examined potential temporal variation in between- and within-population dispersal over an 11-year period in a bird, the dark-eyed junco (Junco hyemalis). We measured between-population dispersal patterns using genetic assignment indices and found yearly variation in which sex was more likely to have immigrated. When we measured within-population spatial genetic structure and mark–recapture dispersal distances, we typically found yearly SBD patterns that mirrored between-population dispersal, indicating common eco-evolutionary causes despite expected differences due to the scale of dispersal. However, in years without detectable between-population sex biases, we found genetic similarity between nearby males within our population. This suggests that, in certain circumstances, ecological pressures may act on within-population dispersal without affecting dispersal between populations. Alternatively, current analytical tools may be better able to detect within-population SBD. Future work will investigate potential causes of the observed temporal variation in dispersal patterns and whether they have greater effects on within-population dispersal.

Genetic estimates of population structure and dispersal in a benthic stream fish

Abstract– Comparing genetic and demographic estimates of dispersal in freshwater fish can improve understanding of movement distributions and population connectivity. Here we examined genetic variation among mottled sculpin (Cottus bairdi) in the Nantahala River (North Carolina, USA) to compare genetic estimates of dispersal with estimates derived from mark–recapture studies of individual movement. Microsatellite‐based analysis of gene flow revealed evidence of strong isolation by distance among locations spanning only 5.6 km and limited dispersal among clusters of sites separated by swift cascades. Estimates of between‐cluster contemporary dispersal rates derived from Bayesian assignment tests ranged from 1% to 6%, with most movement occurring among adjacent clusters in a downstream direction. Evidence of a long‐term net immigration asymmetry and decreasing genetic diversity from downstream to upstream locations indicates that historical patterns of stream colonisation contrast with contemporary dispersal patterns. Our findings are largely consistent with predictions from individual movement patterns but suggest that long moves (>500 m) are more frequent, and maximum dispersal distances are greater than what has been reported from mark–recapture studies. The discrepancy may reflect spatial limitations of mark–recapture methods or temporal variation in dispersal in individuals and populations.

Limits to generality: seasonal and temporal variation in dispersal of an intertidal gastropod

Seasonal and temporal variation can prevent the generalization of ecological models to situations other than those in which they were developed. This paper reports a study specifically designed to test the models that seasonal or temporal variation prevents the accurate prediction of dispersal of intertidal gastropods ( Bembicium auratum) in mangrove forests using models developed on rocky shores. Analysis of variance was used to compare directly the outcomes of experiments replicated several times and in different seasons. In general, the dispersal of Bembicium was very consistent through time, particularly on rocky shores. Differences in the behaviour of Bembicium inhabiting rocky shores and those inhabiting mangrove forests occurred in all runs of the dispersal experiment. The model that seasonal variations in the dispersal of Bembicium inhabiting one habitat prevented prediction of dispersal in the other was rejected. There was, however, some aseasonal temporal variation in the dispersal of Bembicium, particularly at one of the mangrove forests. This suggests that prediction of dispersal in mangrove forests will be less precise than for rocky shores unless further work is done to evaluate causes of temporal variation in that habitat. Experiments must be replicated both spatially and temporally in order to assess the generality of ecological processes, to facilitate proper comparisons with other studies and to provide a sounder basis for the prediction of ecological processes within and between habitats.

Variation in Algal Dispersal and Recruitment: The Importance of Episodic Events

Spatial and temporal variation in dispersal and recruitment of the kelps Macrocystis pyrifera and Pterygophora californica and of filamentous brown algae (FBA) consisting primarily of Ectocarpus siliculosus were examined off southern California, USA. These three taxa of sublittoral brown algae show enormous differences in adult morphology and demography, but release propagules near the bottom that are similar in size, shape, and motility. Their weekly variation in recruitment was measured on replicate frosted glass slides placed at different distances from stands of fertile adults at three sites. For all taxa, significant temporal variation was observed in recruitment at the zoospore source as well as at distances out to 4000 m from the source. For the kelps, this variation was due to variable rates of both zoospore settlement and early postsettlement mortality. In general, recruitment density of both kelps rapidly declined with distance from the adult stand; significantly lower recruitment was observed at as little as 3 m away. In contrast, dispersal of FBA was much greater; no significant decrease in recruitment density was observed out to 500 m. The differences in dispersal between these two algal groups may result from behavioral differences of their zoospores. Unlike those of kelps, zoospores of FBA are positively phototatic. This enables FBA zoospores to remain in the water column longer, thus increasing the distances over which they disperse. The predominant pattern of limited dispersal in the two kelps, however, was not constant over time. Dispersal was greatly expanded during episodic periods of high recruitment that coincided with winter storms. Turbulent water flower associated with these storms may resuspend kelp zoospores normally occurring near the bottom and allow them to be transported greater distances by prevailing currents. Although species characteristics of the adult stand appeared to influence the distribution of recruits, the effect disappeared within 10 m of the stand. At a short—range study site, decreases in spatial variation in recruitment density between the zoospore source and 3 and 10 m away indicated that the distribution of zoospores became more uniform with distance. Likewise at a long—range site, recruitment out to 4000 m appeared to occur uniformly and coincided with recruitment at the zoospore source and at all intermediate distances. This uniformity and coincidence of recruitment indicated that dispersal over longer distances was probably via individual zoospores rather than via clumps of drifting plants or reproductive fragments as suggested in previous studies. Although episodic, such dispersal is probably essential in promoting the persistence of these plants in highly disturbed and unpredictable environments.