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  • Final Report Summary - FANTI-SIZE (FAcilitated Niche creation Through Indirect interactions in SIZE structured ecological communities: Ontogenetic Asymmetries and Alternative-Stable-States)

Final Report Summary - FANTI-SIZE (FAcilitated Niche creation Through Indirect interactions in SIZE structured ecological communities: Ontogenetic Asymmetries and Alternative-Stable-States)

Executive Summary:

FANTI-SIZE: FAcilitated Niche creation Through Indirect interactions in SIZE structured ecological communities: ontogenetic asymmetries and alternative-stable-states

FANTI-SIZE is a Marie Curie Experienced Researcher Fellowship awarded to Dr Tom Cameron, working with Professor Lennart Persson, and hosted by Umeå University in Sweden.

The theme of the project is to understand the role of size structure in prey populations in facilitating indirect interactions between predators in freshwater communities. And more specifically how Intraguild predation and Facilitation emerge from size and stage structured communities. I would argue that by influencing the size distribution of prey populations and communities, founder predator species can influence the likelihood of invasion and persistence of subsequent species; leading to Alternative Stable States.

We are working in structured freshwater lake communities and I am interested specifically in the interaction between YOY European Perch and the macrozooplankton predator Bythotrephes longimanus via their shared zooplankton prey, Holopedium gibberum (See Photos).

Summary of Project Objectives:

During this two year project I will specifically address the following objectives using a mix of laboratory and field mesocosm and structured biomass population modelling.

1. Experimentally determine the ontogenetic asymmetry in candidate species and how their interactions with each other reciprocally influence size structured vital rates.
2. Analyse a theoretic framework that is initially specific to my food web community that can be used to generate predictive hypotheses to test under specific environmental conditions in field mesocosm.
3. Understand under what conditions the absence of indirect facilitative effects prevents the invasion of secondary consumers into a community.
4. Harmonise small scale experimental results with field based observations over a longer temporal scale; more explicitly I aim to test the generality of my conclusions from Objectives 1-3 so that they can be placed into a wider context of Alternative Stable States.

Summary of Work Undertaken during grant period:

During this grant the size-structured functional and numerical responses of the candidate predator species, perch, roach and Bythotrephes, has been determined while feeding on their shared zooplankton prey Holopedium gibbernum. In addition the rate of Intraguild predation on Bythotrephes by perch, and the feeding preferences of either predator on all zooplankton across their zooplankton prey communities have been determined. A number of fully structured community biomass models of this system have been created. Their analysis has helped with the design of the mesocosm experiments in the grant, and led to presentation of preliminary results at international conferences. A seven week time series of all species in 32 mesocosms was collected in summer 2012, based on testing the hypothesis that there was a facilitative interaction between perch and Bythotrephes while they fed on a shared size structured zooplankton prey community. In total this experiment, including the building of the mesocosms, and pumping them with water and initiating animal populations, data collection and the deconstruction of the mesocosms before winter ran from May to September 2012. A complete fully size structured data base of all zooplankton, macroinvertebrate and fish time series for seven experimental lakes from 1992-2012 has been created, checked and completed. Analysis of this database has revealed some interesting results in terms of the interaction between perch and macroinvertebrate predators at multiple spatial and temporal scales. This dataset has led to further projects and analyses than set out in the grant agreement through collaboration with other researchers based in Umeå and elsewhere in Europe (Trondheim and Edinburgh).

Summary of main results during the grant period:

The main results of the project are those that have come from the modelling, the mesocosm experiments and the analysis of the long term lake time series. The initial modelling of the system specific 3 species community predicted that even a small switch away of the primary predator consuming the shared prey and instead predating the secondary predator could cause any facilitative interaction to collapse. The mesocosm experiments revealed firstly that the population growth rate of the secondary predator, Bythotrephes, was highest when it was the only predator in the system. The individual feeding trials also reveal that perch is a formidable predator of Bythotrephes despite its long tail spine. The long term data from the lakes suggest that this long spine may be useful in defending Bythotrephes from the highest density vertebrate predator in the system, larval stage fish, but that the conspicuous swimming behaviour of Bythotrephes perhaps makes it more vulnerable to predation from larger fish. That alone is not evidence that facilitation between predators that share the same prey cannot occur. However, there is also no evidence that where predators are allowed to predate on Holopedium as they would in the lakes, continuously throughout the summer, that any stage specific biomass compensation occurs in Holopedium or indeed any zooplankton prey. The reason for this could be that continuous predation removes any compensatory response or as we interpret this result, that interspecific responses of the zooplankton community are far more important than the interspecific responses of a single zooplankton species in the response to predation. This mesocosm based result was confirmed by analysis of the long term field data across four of the study lakes where it is clear that the driving variables of perch or Bythotrephes effects on zooplankton community structure are the availabilities of their preferred prey species and not the mean or variance in the size of those species.

Summary of Expected Final Results and their impact and Use:

The expected final results, over the course of 2014, will expand on the summary of the main results to date by exploring the potential of facilitative and intraguild predation species interactions in well-studied natural food webs, particularly in relation to predators of different sizes. A key objective moving forward then is to further develop the modelling framework created during the grant to incorporate the difference in mean body size of predators that share the same prey, and their resulting attack rates on each other, into the current Emergent Facilitation theoretical framework. At present two papers have been submitted to good journals for peer review based on the research undertaken in the grant. One paper is based on the outcomes of some of the mesocosm experiments, and the other on the analysis of the long term field data. A third paper, based on the analysis of models, is in progress. There is a great deal of interest in both body size and the role of counter intuitive indirect interactions in the responses of animal communities to environmental change. The results from this IEF suggest that while body size specific and indirect intraspecific responses of life histories to environmental change are possible, their observed effects are lower than that of species specific or interspecific community responses to change. These results then are likely to be of interest to those who wish to understand and/or predict how ecological communities respond to change. Perhaps more importantly these results will place perspective on current trends, and add to the body of evidence that suggests that complex population and community dynamics needs complex models and proxies such as body size are not always appropriate.

The main conclusions of the project so far help us to understand what can lead to failed perch recruitment, and why this may be related to high abundance of small invertebrate predators such as Bythotrephes. These results are of huge socio-economic importance where the native European Bythotrephes has invaded water bodies in North America with ecological, social and financial implications.

Project Website:

Project Researcher contact details:
Dr Tom C Cameron
Lecturer in Freshwater Community Ecology
School of Biological Sciences
University of Essex

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