Author Archives: dmcglinn

Signature of dispersal on community structure

This post was contributed by Rodrigo Barbosa Ferreira who is a PhD candidate in Dr. Karen Beard’s lab. Rodrigo is studying the effects of habitat fragmentation on bromeliad-dependent frogs in Brazil, and was recently awarded the CNR graduate researcher of the year. Take it away Rodrigo.

We recently discussed two papers (listed below) on the role of dispersal limitation:

  • Shurin, J. 2000. Dispersal limitation, invasion resistance, and the structure of pond zooplankton communities. Ecology. 81:3074–3086. (pdf)
  • Seidler, T. G., and J. B. Plotkin. 2006. Seed dispersal and spatial pattern in tropical trees. PLoS Biology 4:2132–2137. (pdf)

During our  discussion we attempted to answer some interesting questions such as:
– What is the driving factor structuring a given community in a given area?
– How important is dispersal for structuring communities?
– Is biological diversity an important factor preventing invasion?

The Shurin (2000) paper is an important one to discuss because the author empirically tested two fundamental paradigms in the emerging field of Invasion Ecology. Specifically, Shurin discusses both the role of dispersal and interspecific interactions on structuring the community composition of zooplankton.

Shurin (2000) begins his abstract stating that “for a species to colonize a site it must both arrive there by dispersal from another site and maintain positive population growth in the local environment”. He carried out two experiments which compared the importance of dispersal ability vs. native community resistance in structuring a community. Using zooplankton as study taxon, Shurin set up enclosures in natural ponds and manipulated several additional ponds. He added invasive species to the local communities and evaluated the establishment of invasive populations through time. In this experiment, he found that only a small portion of the introduced species became established (i.e., most introduced species became extinct). In the following year, he conducted a second experiment where he reduced the abundance of native species by filtering the enclosures. He found out an increase in the success of population establishment of the introduced species. He concludes that dispersal plays an important role determining where the species can reach or potentially colonize. However the local community diversity is the decisive factor excluding potential invaders (Shurin 2000, Fig. 2).

shurin_fig2In recent years, a consensus has emerged in the field of Invasion Ecology on the set of important processes related to species invasion. For example, now it is well recognize that propagule pressure has an important contribution to whether or not an  introduced species becomes established. Shurin mentions this in the Material and Methods section and also on the Discussion where he says “some species introduced in low numbers may have failed to invade because too few propagules were introduced”. In my opinion, a key weakness of this study was that it failed to account for propagule pressure despite of acknowledging the importance of it. In addition to the invaders abundance (that he mentioned) as a potential problem on species establishment, the number of introduction events plays also a major role in invasion. For instance, if he had conducted another introduction event in the enclosures perhaps the introduced species would have established via rescue effects.  However, as I said above, propagule pressure was not a totally recognized important factor influencing non-native species establishment at the time of this publication and therefore should not minimize the importance of these brilliant experiments.

The second paper, by Seidler and Plotkin (2006), contributed to our discussion on dispersal by demonstrating the importance of morphological traits on seed dispersal of trees in tropical region. Dispersal limitation is a potential mechanism for separating species in space and reducing competitive exclusion as stated by Seidler and Plotkin (2006). These authors investigated the spatial distribution of trees in a 50-hectare plot of primary tropical forest. By evaluating the dispersal morphologies and fruit sizes of 561 species, these authors clearly show the importance of this species traits on their spatial distribution. Animal-dispersed species exhibited significantly larger cluster sizes than species not dispersed by animals (Seidler and Plotkin, Fig. 2). This study has important theoretical implications, but I found it very interesting that the morphological traits of the plants could be linked to clustering because clustering is well known to reduce alpha diversity at small spatial scales, as well as, increase turnover and thus increase beta and gamma diversity at larger scales.  Thus this paper seems to imply a link between the individuals’ traits and the community diversity properties.

disperal_fig

Stochastic and Deterministic Mechanisms of Assembly

Recently in seminar we discussed two influential papers:

  • Vellend, B. M. 2010. Conceptual Synthesis in Community Ecology. The Quarterly Review of Biology 85:183–206. (pdf)
  • Chase, J. M. 2007. Drought mediates the importance of stochastic community assembly. Proceedings of the National Academy of Sciences of the United States of America 104:17430–17434. (pdf)

I chose these papers because I feel that they do a good job of both laying the conceptual and practical groundwork necessary to advance  the debate between the relative importance of stochastic and deterministic processes in community ecology.

Before our discussion began there was a flurry of interesting tweets inspired by the readings:

tweet2 tweetsbeth_ross_tweetThese tweets helped set the tone for our discussion and led to some interesting discussion.

The key questions that we discussed during the seminar were:

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Introduction to Community Assembly

The first day of the USU community assembly seminar was a great success. We have a really excellent group of ecologists that seem excited to discuss the latest ideas in community assembly. To get the group all on the same conceptual page and to provide some historical context into the study of community assembly I put together a short lecture that summarizes the existing conceptual framework of community assembly and delves into the origins of the various ideas that it is based upon. The slides to my talk are here, enjoy!

References:
Palmer, M. W. 1994. Variation in species richness – towards a unification of hypotheses. Folia Geobotanica & Phytotaxonomica 29:511–530.

HilleRisLambers, J., P. B. Adler, W. S. Harpole, J. M. Levine, and M. M. Mayfield. 2012. Rethinking Community Assembly through the Lens of Coexistence Theory. Annual Review of Ecology, Evolution, and Systematics 43:227–248.

see the blog’s bibliography for additional references

Seminar Details

wildlife

Printable Course Flyer (pdf)

Biol 6750 sec 007

Graduate Seminar
1 credit hour

Course Description

This course will explore important contemporary papers (from the last 10 years) that are pioneering new methods of studying ecological community assembly.  The course will be organized as a seminar in which each week a different paper or concept is shared with the group.  The emphasis of the course will be on the intersection of different approaches to understanding community assembly including but not limited to the role of functional traits, phylogenetic conservatism, dispersal limitation, environmental filtering, and eco-evolutionary dynamics.  The papers will cover theoretical, experimental, and data-intensive evidence for the importance of different mechanisms underlying species coexistence, abundance, and spatial and temporal distributions.

Day and Time– Thursday, 2pm in BNR 132

Advanced undergraduates allowed with permission.

If you are interested in attending contact:

Dr. Daniel J. McGlinn
Department of Biology, BNR 132
daniel.mcglinn[at]usu.edu
@danmcglinn on twitter