Larval Dispersal and Marine Population Connectivity
TL;DR: Evidence from direct and indirect approaches using geochemical and genetic techniques suggests that populations range from fully open to fully closed and a full understanding of population connectivity has important applications for management and conservation.
Abstract: Connectivity, or the exchange of individuals among marine populations, is a central topic in marine ecology. For most benthic marine species with complex life cycles, this exchange occurs primarily during the pelagic larval stage. The small size of larvae coupled with the vast and complex fluid environment they occupy hamper our ability to quantify dispersal and connectivity. Evidence from direct and indirect approaches using geochemical and genetic techniques suggests that populations range from fully open to fully closed. Understanding the biophysical processes that contribute to observed dispersal patterns requires integrated interdisciplinary approaches that incorporate high-resolution biophysical modeling and empirical data. Further, differential postsettlement survival of larvae may add complexity to measurements of connectivity. The degree to which populations self recruit or receive subsidy from other populations has consequences for a number of fundamental ecological processes that affect population regulation and persistence. Finally, a full understanding of population connectivity has important applications for management and conservation.
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TL;DR: Alternative approaches for assessing population connectivity are described, highlighting the value of combining genetic data with capture‐mark‐recapture methods or other direct measures of movement to elucidate the complex role of dispersal in natural populations.
Abstract: Genetic data are often used to assess ‘population connectivity’ because it is difficult to measure dispersal directly at large spatial scales. Genetic connectivity, however, depends primarily on the absolute number of dispersers among populations, whereas demographic connectivity depends on the relative contributions to population growth rates of dispersal vs. local recruitment (i.e. survival and reproduction of residents). Although many questions are best answered with data on genetic connectivity, genetic data alone provide little information on demographic connectivity. The importance of demographic connectivity is clear when the elimination of immigration results in a shift from stable or positive population growth to negative population growth. Otherwise, the amount of dispersal required for demographic connectivity depends on the context (e.g. conservation or harvest management), and even high dispersal rates may not indicate demographic interdependence. Therefore, it is risky to infer the importance of demographic connectivity without information on local demographic rates and how those rates vary over time. Genetic methods can provide insight on demographic connectivity when combined with these local demographic rates, data on movement behaviour, or estimates of reproductive success of immigrants and residents. We also consider the strengths and limitations of genetic measures of connectivity and discuss three concepts of genetic connectivity that depend upon the evolutionary criteria of interest: inbreeding connectivity, drift connectivity, and adaptive connectivity. To conclude, we describe alternative approaches for assessing population connectivity, highlighting the value of combining genetic data with capture-mark-recapture methods or other direct measures of movement to elucidate the complex role of dispersal in natural populations.
699 citations
TL;DR: How adequately genetic factors are currently incorporated into population viability analysis (PVA) models used to estimate minimum viable population sizes is assessed, and population size thresholds of the IUCN Red List criteria for threatened species that were derived from genetic considerations are related.
679 citations
Cites background from "Larval Dispersal and Marine Populat..."
...Recent research also suggests that marine organisms disperse less than previously assumed (Cowen and Sponaugle, 2009; Jones et al., 2009)....
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TL;DR: A better understanding of the relative roles of species sorting, mass effects and dispersal limitation in affecting aquatic metacommunities requires the following: characterising dispersal rates more directly or adopting better proxies than have been used previously; considering the nature of aquatic networks; and combining correlative and experimental approaches.
Abstract: Summary
Metacommunity ecology addresses the situation where sets of local communities are connected by the dispersal of a number of potentially interacting species. Aquatic systems (e.g. lentic versus lotic versus marine) differ from each other in connectivity and environmental heterogeneity, suggesting that metacommunity organisation also differs between major aquatic systems. Here, we review findings from observational field studies on metacommunity organisation in aquatic systems.
Species sorting (i.e. species are ‘filtered’ by environmental factors and occur only at environmentally suitable sites) prevails in aquatic systems, particularly in streams and lakes, but the degree to which dispersal limitation interacts with such environmental control varies among different systems and spatial scales. For example, mainstem rivers and marine coastal systems may be strongly affected by ‘mass effects’ (i.e. where high dispersal rates homogenise communities to some degree at neighbouring localities, irrespective of their abiotic and biotic environmental conditions), whereas isolated lakes and ponds may be structured by dispersal limitation (i.e. some species do not occur at otherwise-suitable localities simply because sites with potential colonists are too far away). Flow directionality in running waters also differs from water movements in other systems, and this difference may also have effects on the role of dispersal in different aquatic systems.
Dispersal limitation typically increases with increasing spatial distance between sites, mass effects potentially increase in importance with decreasing distance between sites, and the dispersal ability of organisms may determine the spatial extents at which species sorting and dispersal processes are most important.
A better understanding of the relative roles of species sorting, mass effects and dispersal limitation in affecting aquatic metacommunities requires the following: (i) characterising dispersal rates more directly or adopting better proxies than have been used previously; (ii) considering the nature of aquatic networks; (iii) combining correlative and experimental approaches; (iv) exploring temporal aspects of metacommunity organisation and (v) applying past approaches and statistical methods innovatively for increasing our understanding of metacommunity organisation.
664 citations
Stanford University1, University of California, Santa Barbara2, University of California, Santa Cruz3, The Nature Conservancy4, Marine Conservation Institute5, College of William & Mary6, Oregon State University7, University of North Carolina at Chapel Hill8, University of California, Riverside9, National Marine Fisheries Service10, National Ocean Service11, University of Maine12
TL;DR: In this article, the authors identify ecological principles for MSP based on a synthesis of previously suggested and/or operationalized principles, along with recommendations generated by a group of twenty ecologists and marine scientists with diverse backgrounds and perspectives on MSP.
478 citations
Scottish Association for Marine Science1, National Institute for Environmental Studies2, Imperial College London3, University of California, Santa Barbara4, University of the Sunshine Coast5, University of Queensland6, University of Erlangen-Nuremberg7, Museum für Naturkunde8, Edith Cowan University9, Aberystwyth University10, Commonwealth Scientific and Industrial Research Organisation11
TL;DR: Ocean warming will cause widespread changes in species richness and assemblage composition over coming decades, with important implications for both conservation management and international ocean governance as mentioned in this paper, and this is a major concern.
Abstract: Ocean warming will cause widespread changes in species richness and assemblage composition over coming decades, with important implications for both conservation management and international ocean governance.
446 citations
References
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5,446 citations
TL;DR: Analytical theory shows that there is a simple relationship between M̂ and geographic distance in both equilibrium and non‐equilibrium populations and that this relationship is approximately independent of mutation rate when the mutation rate is small.
Abstract: It is shown that for allele frequency data a useful measure of the extent of gene flow between a pair of populations is M∘=(1/FST-1)/4, which is the estimated level of gene flow in an island model at equilibrium. For DNA sequence data, the same formula can be used if FST is replaced by NST . In a population with restricted dispersal, analytic theory shows that there is a simple relationship between M and geographic distance in both equilibrium and non-equilibrium populations and that this relationship is approximately independent of mutation rate when the mutation rate is small. Simulation results show that with reasonable sample sizes, isolation by distance can indeed be detected and that, at least in some cases, non-equilibrium patterns can be distinguished. This approach to analyzing isolation by distance is used for two allozyme data sets, one from gulls and one from pocket gophers.
2,499 citations
"Larval Dispersal and Marine Populat..." refers background in this paper
...The level of such ecologically relevant exchange is several orders of magnitude larger than the level of exchange required for the maintenance of genetic homogeneity among subpopulations (which requires only a few individuals per generation; Slatkin 1993)....
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...…demographic rates of exchange in marine organisms have dominated the recent literature: utilization of the stepping-stone model (Wright 1943, Slatkin 1993) via estimation of isolation-by-distance, and more recently, the use of assignment tests (Manel et al. 2005) to more directly link…...
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TL;DR: Together with the development and refinement of mathematical models, this promises a deeper, more mechanistic understanding of dispersal processes and their consequences.
Abstract: Growing interest in spatial ecology is promoting new approaches to the study of seed dispersal, one of the key processes determining the spatial structure of plant populations. Seed-dispersion patterns vary among plant species, populations and individuals, at different distances from parents, different microsites and different times. Recent field studies have made progress in elucidating the mechanisms behind these patterns and the implications of these patterns for recruitment success. Together with the development and refinement of mathematical models, this promises a deeper, more mechanistic understanding of dispersal processes and their consequences.
1,884 citations
"Larval Dispersal and Marine Populat..." refers methods in this paper
...Terrestrial botanists have been studying dispersal of seeds for many years (see Nathan & Muller-Landau 2000), utilizing similar methods (e.g., genetic markers to establish source of seeds) to understand the spatial extent of dispersal....
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TL;DR: The results show that even a single nonrecombining genetic locus can provide substantial power to test the hypothesis of no ongoing migration and/or to test models of symmetric migration between the two populations.
Abstract: A Markov chain Monte Carlo method for estimating the relative effects of migration and isolation on genetic diversity in a pair of populations from DNA sequence data is developed and tested using simulations. The two populations are assumed to be descended from a panmictic ancestral population at some time in the past and may (or may not) after that be connected by migration. The use of a Markov chain Monte Carlo method allows the joint estimation of multiple demographic parameters in either a Bayesian or a likelihood framework. The parameters estimated include the migration rate for each population, the time since the two populations diverged from a common ancestral population, and the relative size of each of the two current populations and of the common ancestral population. The results show that even a single nonrecombining genetic locus can provide substantial power to test the hypothesis of no ongoing migration and/or to test models of symmetric migration between the two populations. The use of the method is illustrated in an application to mitochondrial DNA sequence data from a fish species: the threespine stickleback (Gasterosteus aculeatus).
1,338 citations
TL;DR: It is argued that demographic theory suggests that, except under restrictive and unlikely conditions, recruitment must influence local population density to some extent, and the question as to whether the size of a particular population is limited by recruitment is misguided.
Abstract: The majority of marine populations are demographically open; their replenishment is largely or exclusively dependent on a supply of juveniles from the plankton. In spite of much recent research, no consensus has yet been reached regarding the importance of recruitment relative to other demographic processes in determining local population densities. We argue 1. that demographic theory suggests that, except under restrictive and unlikely conditions, recruitment must influence local population density to some extent. Therefore, 2. the question as to whether the size of a particular population is limited by recruitment is misguided. Finally, 3. the effect of recruitment on population size can be difficult to detect but is nonetheless real. A major weakness of most existing studies is a lack of attention to the survival of recruits over appropriate scales of time and space. Acknowledgment of the multifactorial determination of population density should guide the design of future experimental studies of the demography of open populations.
1,290 citations
"Larval Dispersal and Marine Populat..." refers background in this paper
...New settlers are usually susceptible to high predation (Caley et al. 1996, Hunt & Scheibling 1997) and their survival can be related to their condition at settlement....
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