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How do dispersal costs and habitat selection influence realized population connectivity?

Authors: Scott C Burgess, Eric A Treml and Dustin J Marshall

Published in: Ecology, volume 93, issue 6, doi: 10.1890/11-1656.1

Abstract

Despite the importance of dispersal for population connectivity, dispersal is often costly to the individual.

A major impediment to understanding connectivity has been a lack of data combining the movement of individuals and their survival to reproduction in the new habitat (realized connectivity).

Although mortality often occurs during dispersal (an immediate cost), in many organisms costs are paid after dispersal (deferred costs). It is unclear how such deferred costs influence the mismatch between dispersal and realized connectivity.

Through a series of experiments in the field and laboratory, we estimated both direct and indirect deferred costs in a marine bryozoan (Bugula neritina). We then used the empirical data to parameterize a theoretical model in order to formalize predictions about how dispersal costs influence realized connectivity.

Individuals were more likely to colonize poor-quality habitat after prolonged dispersal durations. Individuals that colonized poor-quality habitat performed poorly after colonization because of some property of the habitat (an indirect deferred cost) rather than from prolonged dispersal per se (a direct deferred cost).

Our theoretical model predicted that indirect deferred costs could result in nonlinear mismatches between spatial patterns of potential and realized connectivity.

The deferred costs of dispersal are likely to be crucial for determining how well patterns of dispersal reflect realized connectivity. Ignoring these deferred costs could lead to inaccurate predictions of spatial population dynamics.

Full paper

Burgess SC, Treml EA, Marshall DJ (2012) How do dispersal costs and habitat selection influence realized population connectivity? Ecology 93: 1378–1387 PDFPDF 622 KB doi: 10.1890/11-1656.1

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Published paper: Minimal increase in genetic diversity enhances predation resistance

Authors: Kai S Koh, Carsten Matz, Chuan H Tan, Hoang L Le, Scott A Rice, Dustin J Marshall, Peter D Steinberg and Steffan Kjelleberg

Published in: Molecular Ecology, volume 21, issue 7, doi: 10.1111/j.1365-294X.2011.05415.x

Abstract

The importance of species diversity to emergent, ecological properties of communities is increasingly appreciated, but the importance of within-species genetic diversity for analogous emergent properties of populations is only just becoming apparent.

Here, the properties and effects of genetic variation on predation resistance in populations were assessed and the molecular mechanism underlying these emergent effects was investigated.

Using biofilms of the ubiquitous bacterium Serratia marcescens, we tested the importance of genetic diversity in defending biofilms against protozoan grazing, a main source of mortality for bacteria in all natural ecosystems.

S. marcescens biofilms established from wild-type cells produce heritable, stable variants, which when experimentally combined, persist as a diverse assemblage and are significantly more resistant to grazing than either wild type or variant biofilms grown in monoculture.

This diversity effect is biofilm-specific, a result of either facilitation or resource partitioning among variants, with equivalent experiments using planktonic cultures and grazers resulting in dominance by a single resistant strain.

The variants studied are all the result of single nucleotide polymorphisms in one regulatory gene suggesting that the benefits of genetic diversity in clonal biofilms can occur through remarkably minimal genetic change.

The findings presented here provide a new insight on the integration of genetics and population ecology, in which diversity arising through minimal changes in genotype can have major ecological implications for natural populations.

Full paper

Koh KS, Matz C, Tan CH, Le HL, Rice SA, Marshall DJ, Steinberg PP, Kjelleberg S (2012) Minimal increase in genetic diversity enhances predation resistance. Molecular Ecology 21: 1741–1753 PDFPDF 681 KB doi: 10.1111/j.1365-294X.2011.05415.x

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Genetic diversity increases population productivity in a sessile marine invertebrate

Authors: J David Aguirre and Dustin J Marshall

Published in: Ecology, volume 93, issue 5, doi: 10.1890/11-1448.1

Abstract

Reductions in genetic diversity can have widespread ecological consequences: populations with higher genetic diversity are more stable, productive and resistant to disturbance or disease than populations with lower genetic diversity.

These ecological effects of genetic diversity differ from the more familiar evolutionary consequences of depleting genetic diversity, because ecological effects manifest within a single generation.

If common, genetic diversity effects have the potential to change the way we view and manage populations, but our understanding of these effects is far from complete, and the role of genetic diversity in sexually reproducing animals remains unclear.

Here, we examined the effects of genetic diversity in a sexually reproducing marine invertebrate in the field. We manipulated the genetic diversity of experimental populations and then measured individual survival, growth, and fecundity, as well as the size of offspring produced by individuals in high and low genetic diversity populations.

Overall, we found greater genetic diversity increased performance across all metrics, and that complementarity effects drove the increased productivity of our high-diversity populations.

Our results show that differences in genetic diversity among populations can have pervasive effects on population productivity within remarkably short periods of time.

Full paper

Aguirre JD, Marshall DJ (2012) Genetic diversity increases population productivity in a sessile marine invertebrate. Ecology 93: 1134–1142 PDFPDF 1.3 MB doi: 10.1890/11-1448.1

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Advantages and disadvantages of interference-competitive ability and resource-use efficiency when invading established communities

Authors: Simon P Hart and Dustin J Marshall

Published in: Oikos, volume 121, issue 3, doi: 10.1111/j.1600-0706.2011.19557.x

Abstract

Invaders into established communities must overcome low resource availability. To establish, invaders must either appropriate resources from existing individuals through interference competition or efficiently use the small amount of resource that remains. Although both strategies may be important, they are rarely considered together and, in particular, resource-use efficiency is often ignored in systems dominated by interference competition.

To identify the traits that confer invasion success, we experimentally invaded resource patches in established communities with multiple species from two functional groups that differ in interference competitive ability and resource-use efficiency.

In contrast to previous assessments, we show that resource-use efficiency can facilitate invasion in systems dominated by interference competition. Furthermore, large resource requirements can be a liability when establishing because interference competition is inherently costly and so cannot fully compensate for limitations in the primary resource.However, we also show that there is a tradeoff in performance among functional groups between small and large resource gaps.

Our results suggest we modify the way we view and manage species invasion in systems dominated by interference competition.

Full paper

Hart SJ, Marshal DJ (2012) Advantages and disadvantages of interference-competitive ability and resource-use efficiency when invading established communities. Oikos, 121: 396–402 PDFPDF 132 KB doi: 10.1111/j.1600-0706.2011.19557.x

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Does genetic diversity reduce sibling competition?

Authors: J. David Aguirre and Dustin J. Marshall

Published in: Evolution, volume 6, issue 1, doi: 10.1111/j.1558-5646.2011.01413.x

Abstract

An enduring hypothesis for the proximal benefits of sex is that recombination increases the genetic variation among offspring and that this genetic variation increases offspring performance. A corollary of this hypothesis is that mothers that mate multiply increase genetic variation within a clutch and gain benefits due to genetic diversity alone.

Many studies have demonstrated that multiple mating can increase offspring performance, but most attribute this increase to sexual selection and the role of genetic diversity has received less attention. Here, we used a breeding design to generate populations of full-siblings, half-siblings, and unrelated individuals of the solitary ascidian Ciona intestinalis. Importantly, we preclude the potentially confounding influences of maternal effects and sexual selection.

We found that individuals in populations with greater genetic diversity had greater performance (metamorphic success, postmetamorphic survival, and postmetamorphic size) than individuals in populations with lower genetic diversity. Furthermore, we show that by mating with multiple males and thereby increasing genetic variation within a single clutch of offspring, females gain indirect fitness benefits in the absence of mate-choice.

Our results show that when siblings are likely to interact, genetic variation among individuals can decrease competition for resources and generate substantial fitness benefits within a single generation.

Full paper

Aguirre JD, Marshall DJ (2012) Does genetic diversity reduce sibling competition? Evolution, 66-1: 94–102 PDFPDF 688 KB doi: 10.1111/j.1558-5646.2011.01413.x

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PhD positions available: the evolutionary ecology and/or quantative genetics of marine invertebrates

Two fully-funded PhD stipends are available to students interested in working on the evolutionary ecology of marine invertebrates in Dr Dustin Marshall’s group.

The stipends include all course fees plus ~$25,000 AUD per annum tax-free (the equivalent of  approx. $33,000 before tax) with no teaching requirements.

I can guarantee funding of project costs including the costs of attending at least one conference per year.

Project start dates can be any time in 2012.

Interested students should send their CVs, a brief statement of their interests and the contact details of two referees.

To be eligible, applicants must have completed at least one year of post-graduate research and ideally a masters degree.

Preference will be given to those with strong quantitative skills.