Kenneth S. Norris Rancho Marino Reserve

01 Jun, 01 AM - 02 Jun, 10 AM

Understanding the forces that structure and maintain natural communities has long been of interests to ecologists (Gause 1934; Hutchinson 1959; Janzen 1970; Connell 1978; Shmida and Wilson 1985; Chesson 2000; Chase 2005), and a large body of theories developed to explain diversity have focused on the ability of predators to regulate prey populations (and subsequently those of primary producers) (Janzen 1970; Trussell, Ewanchuk et al. 2004; Berger, Gese et al. 2008). These theories have traditionally focused on direct effects of predators such as consumption due to the ease of sampling methods and the simplicity added to ecological models (Hairston, Smith et al. 1960; Holt, Grover et al. 1994; Peckarsky, Abrams et al. 2008). A subset of these theories have developed around the keystone predator hypothesis, which states that certain predators can have an impact on prey populations beyond that predicted simply by the amount of biomass consumed (Paine 1966; Paine 1969). This was first noted in systems where predators exhibit a preference for prey that are competitive dominants; removal of such prey increases the access of inferior competitors to resources. Much of this theory was developed through observations of rocky intertidal communities, notably those along the west coast of North America (Paine 1966). In this system, Pisaster ochraceus has been termed a keystone predator due to selective predation on various Mytilus species. Mytilus are the dominant competitors for space in the intertidal and thus selective predation increases open space for inferior competitors. Removal or exclusion of Pisaster results in decreased diversity because Mytilus outcompete other species for space (Paine 1966). The Pisaster-Mytilus relationship and its impact on rocky intertidal community diversity is considered a textbook example of keystone predation in ecology (Paine 1966; Paine 1969; Peckarsky, Abrams et al. 2008) and has been the subject of numerous studies including tests of environmental interactions and per-capita and per-population predation rates along the west coast of North America (Sanford 2002; Menge, Blanchette et al. 2004; Petes, Mouchka et al. 2008). However, a full understanding of Pisaster?s function as a keystone predator is still lacking, particularly in understanding the importance of non-consumptive effects (NCE) of Pisaster in regulating intertidal communities. In contrast to consumptive effects (CE, also termed density effects), which are the impact predators have on prey populations by removing individuals, NCE (also termed trait effects) are the influence the mere presence of a predator has on prey populations (Luttbeg and Kerby 2005). Recent studies in a variety of systems have emphasized the potential importance of NCE of predators on prey populations (Anderson, Kiesecker et al. 2001; Werner and Peacor 2003; Trussell, Ewanchuk et al. 2004; Wojdak and Luttbeg 2005; Trussell, Ewanchuk et al. 2006; Berger, Gese et al. 2008). In a recent meta-analysis Preisser et al. found that the impacts of NCE on prey and community measures are at least as important as consumptive effects (CE) and that their influence often reverberates further through ecological communities (2005). A recent review of other ?classic? examples of communities regulated by predation have suggested that the importance of NCE is often overlooked (Peckarsky, Abrams et al. 2008). Moreover, the importance of NCE to community regulation by keystone predators remains to be investigated. It has been suggested that keystone species may be divided into ?keystone consumers? and ?keystone intimidators? due to the means by which they influence community diversity. However, empirical tests distinguishing the role of NCE in community regulation by Pisaster are lacking. The purpose of this project is to explore the importance of NCE of Pisaster to rocky intertidal community diversity through a set of replicated exclusion experiments in a field setting and thus attempt to disentangle and compare the importance of CE and NCE to this keystone predator. This would be the first published attempt to discern the impact of NCE of Pisaster on west coast intertidal sites. This project would also offer valuable insight concerning the importance of NCE to keystone predators. Preliminary work I have conducted in lab settings suggests the presence of Pisaster can impact morphological and behavioral responses of intertidal species. Though multiple other researchers have examined the impact of selective predator removal or exclusion from rocky intertidal sites (Paine 1974; Navarrete and Menge 1996; Menge, Blanchette et al. 2004), a systematic study of CE and NCE has not been performed and thus their impact, interaction, and importance are not clear. Through a systematic set of predator-exclusion and predator-removal experiments, questions concerning the relative importance of NCE to rocky intertidal sites may be answered. The rich history of data concerning the Pisaster-Mytilus interaction and its impact on community diversity provide an excellent system for this work. The availability of optimal sites in the Reserve system offers areas to also study how various environmental factors may impact the relative strength of NCE and CE. Questions concerning the scale of predator impact and integrity of predator cues may also be addressed. Through this project I aim to test the following hypotheses: 1. The impacts of NCE of Pisaster on intertidal community diversity (species composition, evenness, percent cover) and production (growth) are at least as great as those of CE. 2. The impacts of NCE will vary with spatial distance from the source of cues, i.e. distance of Pisaster exclosure. 3. The proportion of total Pisaster effect that is dependent on NCE will vary inversely with the local population size of Pisaster. 4. The total impacts of NCE will vary less between locations than those of CE, meaning NCE will be of greater relevance to areas with small or temporally variable populations of Pisaster. In order to distinguish the impact of NCE and CE of Pisaster, exclusion experiments will be carried out in rocky intertidal sites at three reserve locations: Bodega Marine Reserve, Kenneth S. Norris Rancho Marino Reserve, and Landels-Hill Big Creek Reserve. The use of multiple sites will allow for regional comparisons of the importance of NCE and also aid in validating results at a larger scale while also offering insight into interactions between environmental variables and the relative importance of NCE and CE. Multiple sites may also provide information for use in metacommunity models attempting to incorporate the importance of NCE, a recently noted need in a review of the impact of NCE on metacommunities(Preisser and Bolnick 2008). Reserve locations offer an optimal site for experiment placement due to their protection and pristine environments. At each site, 4 treatments will be tested in triplicate: combined effects of CE and NCE, CE, NCE, and no effect (control). For each experimental plot a 3?x3? area of existing rocky intertidal community will be selected. Mytilus specimens in the plot will be marked by filing a notch on the posterior shell edge so growth patterns may be analyzed (Blanchette, Helmuth et al. 2007). For the combined effect treatment, the plots will not be caged and will only be marked at the four corners of the plot with galvanized bolts for future sampling. For the CE and control treatments, the plots will be placed in areas where large scale Pisaster removal is possible or where Pisaster are not common (small outcroppings or rocks). For the CE treatment, plots will be caged and the impacts of CE will be mimicked by manual removal of Mytilus. Long term data for the region and previous work (Navarrete and Menge 1996; Menge, Blanchette et al. 2004) will be consulted for use in estimating ?normal? CE of Pisaster on Mytilus density. Community samples will also be conducted to establish a baseline Pisaster density for the experimental locations. Control sites will be placed near CE plots but no manual removal of Mytilus will occur. NCE treatments will be examined by caging plots in areas where Pisaster are present. For analysis, each 3?x3? plot will be further subdivided into thirty-six 6?x6? subplots. Each subplot will be sampled monthly for species composition, evenness, and percent cover. Digital photographs will be used to monitor changes in percent cover over time. At the conclusion of the experiment, growth will be measured in 25 randomly selected mussels from each plot. Plots will be established in early June and maintained for three months, with Pisaster removal as needed. By marking existing intertidal communities instead of seeding cleaned areas, the project will be able to reach completion during the summer. Data will be analyzed for significant differences among and within treatments. By keeping the community data separated by subplot, the influence of NCE in relation to spatial separation from cues may be analyzed. Data of change over time will also offer information on how long intertidal communities take to respond to a removal of Pisaster cues.

Visit #16497 @Kenneth S. Norris Rancho Marino Reserve

Approved

Under Project # 10726 | Research

The Impact of Non-consumptive Effects of Pisaster ochraceus on Rocky Intertidal Community Diversity

graduate_student - University of California, Santa Barbara

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John Gosnell Jun 1 - 2, 2009 (2 days)

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Day Use Only 1 Jun 1 - 2, 2009