Predictability and constraints on the structure of ecological communities in the context of climate change

Ecologists must increasingly balance the need for accurate predictions about how ecosystems will be affected by climate change, against the fact that making such predictions at the ecosystem-level may be infeasible. Although information about responses of individual species to a changing environment is increasing, scaling such information to the community level is challenging. To date, predicting responses of ecological communities to climate change is constrained by limited theoretical and empirical knowledge about the response of communities and ecosystems to change. My dissertation addresses several knowledge gaps in our understanding of community structure under climate change. This research draws from a rich experimental tradition in the species-diverse model ecosystem of the US Pacific Northwest rocky intertidal to test ecological theory. In Chapter 2, I assessed whether the response of multiple species of coralline algae to global change could be predicted from basic first principles of chemistry, physiology, and ecology. Given the rate of global change, and the time-consuming process of experimentally determining species responses to climate change, I hypothesized that species can be grouped using existing theory, either by their evolutionary relatedness or by their ecological traits, such that climate responses are similar within a group. Such a scheme would greatly reduce the number of experiments needed to characterize species climate vulnerability, requiring the characterization of the response of groups of species to climate change, rather than individual species. Using a suite of five co-occurring species of intertidal articulated coralline algae (Corallina vancouveriensis, Corallina officinalis, Bossiella plumosa, Bossiella orbiginiana, and Calliarthron tuberculosum), I applied this framework to generate ten mutually exclusive hypotheses that could explain organismal response to ocean acidification, a consequence of global climate change that threatens marine calcifying species. I found that all species had similar responses to ocean acidification, and that responses were generally predicted by the body size of the individual. Despite the power that such a framework provides in understanding group-level response to climate change, predicting community-level response requires knowledge of how organisms affect one another. In Chapter 3, I quantified species interactions in a series of removal experiments to estimate the reciprocal effects between a canopy-forming intertidal kelp (Saccharina sessilis) and a suite of understory species that persist beneath the kelp canopy. This experiment was replicated in different oceanographic conditions across a large latitudinal gradient, as a step towards understanding how interactions might change with climate change. However, the experiment demonstrated that interactions between the canopy and understory were consistent among different environmental conditions. Furthermore, the strongest effect was that of understory species, particularly articulated coralline turf algae, on the canopy species. The coralline turf algae both facilitated the recruitment of the canopy species and buffered the canopy from abiotic stress during its adult life stage. Combining experimental results and observational surveys, a hypothesized interaction network for these species was constructed, highlighting the importance of direct and indirect species interactions in promoting species coexistence. A long-standing controversy in ecology is whether or not species interactions can be inferred from observational data, as opposed to from experimental tests. Although the rocky intertidal ecosystem is unique for its ease of experimental manipulation, quantifying species interactions experimentally is often difficult or impossible. As an alternative, many have turned to statistical methods to estimate species interactions from observational data, namely, from patterns in species pairwise co-occurrences. In Chapter 4, I examined these co-occurrence methods and their potential relationship to experimentally measured species interactions. I first used a suite of different co-occurrence methods to generate a set of predicted species interactions of macrophytes and invertebrates from observational surveys conducted in the rocky intertidal zone of Oregon. I then compared the predicted species interactions to the same pairwise species interactions determined experimentally and assembled from the literature. Overall, of the seven methods tested, each generated a different set of predicted species interactions from the same data, and all methods predicted interactions that did not match those in the experimental database. Thus, predicting species interactions from patterns in occurrence remains elusive. Importantly, much work remains to be done to understand the link between species co-occurrences and their actual interactions with one another on the landscape. A key limiting frontier in climate change ecology is determining the influence of species interactions on species distributions across the landscape, and the sensitivity of such interactions to changes in climate. Finally, in Chapter 5, I used theory from the published literature and knowledge from my previous chapters to make predictions the recovery of low rocky intertidal communities after a disturbance. The process of community development after disturbance has been studied in many ways, from the successional studies of the early 1900s, to modern community assembly theory. In recent years, a focus on the unpredictability of community assembly has emerged, paying particular attention to the role of historical contingency, or priority effects, in determining the recovery trajectory of a community. Priority effects occur when the arrival of a species after a disturbance inalterably changes the composition of the developing community, driving the assembly of widely different communities at a small spatial scale. I conducted a community assembly experiment in three different low intertidal zone community "types", each characterized by different dominant macrophyte species (Saccharina sessilis, Phyllospadix spp., and algal "turfs"). Replicating this experiment at six sites along the Oregon coast, I found that both regional and local dynamics constrain the recovery of communities after disturbance. Half of the time, the community returned to the state of the nearby community type. The remaining communities were influenced by priority effects that could be predicted based on 1) regional dynamics favoring some species over others, or 2) the timing of arrival of important facilitating species. Overall, understanding the dynamic relationship between the persistence of diverse communities and a changing environment remains one of the challenges of our time. My dissertation highlights some of the challenges in predicting the future composition of communities under climate change, but also provides some ways forward. Integration of experimental, theoretical, and observational studies builds the scaffolding of prediction, whereby understanding the constraints on species physiology, the interactions among species, and community assembly can help frame the context in which predictions are made.Keywords: Rocky Intertidal, Algae, Community Ecology, Ecology, Kelp, Climate Change Ecolog

The complex net effect of reciprocal interactions and recruitment facilitation maintains an intertidal kelp community

1. Theoretical and empirical ecology has transitioned from a focus on the role of negative interactions in species coexistence to a more pluralistic view that acknowledges that coexistence in natural communities is more complex, and depends on species interactions that vary in strength, sign, and reciprocity, and such contexts as the environment and life-history stage. 2. We used a whole-community approach to examine how species interactions contribute to the maintenance of a rocky intertidal macroalgal canopy–understorey assemblage. We determined both the types of interactions in this network, and whether interactions were sensitive to environmental gradients. 3. Focusing on a structurally dominant canopy kelp Saccharina sessilis, and its diverse co-occurring understorey assemblage, we evaluated the role of the understorey in controlling S. sessilis recruitment and quantified the reciprocal effect of the S. sessilis canopy and understorey on one another using a removal experiment replicated across 600 km of coastline. We determined the sensitivity of interactions to natural variation in light and nutrient availability (replicated among four regions on the N.E. Pacific coast), and under different wave conditions (three wave regimes). 4. Surprisingly, species interactions were similar across sites and thus not context-dependent. Unexpectedly, the understorey community had a strong positive effect on the S. sessilis canopy, whereby the adult canopy decreased dramatically following understorey removal. Additionally, S. sessilis recruitment depended on the presence of understorey coralline algal turf. In turn, the canopy had a neutral effect on the coralline understorey, but a negative effect on non-calcifying algal turfs, likely eventually generating positive indirect canopy effects on the coralline understorey. Density-dependent intraspecific competition between S. sessilis adults and recruits may moderate this positive feedback between the S. sessilis canopy and coralline understorey. 5. Synthesis. Our research highlights the importance of positive interactions for coexistence in natural communities, and the necessity of studying multiple life-history stages and reciprocal species interactions in order to elucidate the mechanisms that maintain diversity.Keywords: marine, plant-plant interactions, aquatic plant ecology, positive interactions, environmental gradients, benthic, macroalga

Solutions for Recovering and Sustaining the Bounty of the Ocean Combining Fishery Reforms, Rights-Based Fisheries Management, and Marine Reserves

Food security, economic opportunities, and other benefits provided by a healthy ocean are in jeopardy because of years of overexploitation of many fisheries, and the challenges will intensify in many locales as climate and the environment continue to change. The good news is that solutions are gaining traction. Mandates to end overfishing that use scientifically determined catch limits and rights-based approaches to fishery management have produced impressive results in ending overfishing and recovering depleted stocks. Similarly, spatial protections, such as fully protected marine reserves, are increasing the diversity, size, and abundance of species within reserves; some of that bounty reaches fished areas outside of them. We review the effects of combining catch limits, rights-based fisheries approaches, and establishment of marine reserves and discuss additional advantages of these combined solutions in securing sustainable and profitable fisheries, community goals, and healthy ecosystems. This paper highlights the contribution of emerging science-based solutions and the steps needed to replicate and scale these successes. Triple-wins for the environment, the economy, and society can be achieved through integrated fisheries management and protection as conscious steps toward reversing the current degradation of our ocean’s living resources.This manuscript is based on a keynote lecture given by Jane Lubchenco at One Planet, One Ocean: The 2nd International Ocean Research Conference, Barcelona, Spain, November 17–21, 2014. This is the publisher’s final pdf. The published article is copyrighted by the Oceanography Society and can be found at: http://www.tos.org/oceanography/archive/28-2_barner.htm

A Network Perspective for Community Assembly

Species interactions are responsible for many key mechanisms that govern the dynamics of ecological communities. Variation in the way interactions are organized among species results in different network structures, which translates into a community's ability to resist collapse and change. To better understand the factors involved in dictating ongoing dynamics in a community at a given time, we must unravel how interactions affect the assembly process. Here, we build a novel, integrative conceptual model for understanding how ecological communities assemble that combines ecological networks and island biogeography theory, as well as the principles of niche theory. Through our conceptual model, we show how the rate of species turnover and gene flow within communities will influence the structure of ecological networks. We conduct a preliminary test of our predictions using plant-herbivore networks from differently-aged sites in the Hawaiian archipelago. Our approach will allow future modeling and empirical studies to develop a better understanding of the role of the assembly process in shaping patterns of biodiversity

Evaluating Temporal Consistency in Marine Biodiversity Hotspots

With the ongoing crisis of biodiversity loss and limited resources for conservation, the concept of biodiversity hotspots has been useful in determining conservation priority areas. However, there has been limited research into how temporal variability in biodiversity may influence conservation area prioritization. To address this information gap, we present an approach to evaluate the temporal consistency of biodiversity hotspots in large marine ecosystems. Using a large scale, public monitoring dataset collected over an eight year period off the US Pacific Coast, we developed a methodological approach for avoiding biases associated with hotspot delineation. We aggregated benthic fish species data from research trawls and calculated mean hotspot thresholds for fish species richness and Shannon’s diversity indices over the eight year dataset. We used a spatial frequency distribution method to assign hotspot designations to the grid cells annually. We found no areas containing consistently high biodiversity through the entire study period based on the mean thresholds, and no grid cell was designated as a hotspot for greater than 50% of the time-series. To test if our approach was sensitive to sampling effort and the geographic extent of the survey, we followed a similar routine for the northern region of the survey area. Our finding of low consistency in benthic fish biodiversity hotspots over time was upheld, regardless of biodiversity metric used, whether thresholds were calculated per year or across all years, or the spatial extent for which we calculated thresholds and identified hotspots. Our results suggest that static measures of benthic fish biodiversity off the US West Coast are insufficient for identification of hotspots and that long-term data are required to appropriately identify patterns of high temporal variability in biodiversity for these highly mobile taxa. Given that ecological communities are responding to a changing climate and other environmental perturbations, our work highlights the need for scientists and conservation managers to consider both spatial and temporal dynamics when designating biodiversity hotspots

Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem

While there is a persistent inverse relationship between latitude and species diversity across many taxa and ecosystems, deviations from this norm offer an opportunity to understand the conditions that contribute to large-scale diversity patterns. Marine systems, in particular, provide such an opportunity, as marine diversity does not always follow a strict latitudinal gradient, perhaps because several hypothesized drivers of the latitudinal diversity gradient are uncorrelated in marine systems. We used a large scale public monitoring dataset collected over an eight year period to examine benthic marine faunal biodiversity patterns for the continental shelf (55–183 m depth) and slope habitats (184–1280 m depth) off the US West Coast (47°20′N—32°40′N). We specifically asked whether marine biodiversity followed a strict latitudinal gradient, and if these latitudinal patterns varied across depth, in different benthic substrates, and over ecological time scales. Further, we subdivided our study area into three smaller regions to test whether coast-wide patterns of biodiversity held at regional scales, where local oceanographic processes tend to influence community structure and function. Overall, we found complex patterns of biodiversity on both the coast-wide and regional scales that differed by taxonomic group. Importantly, marine biodiversity was not always highest at low latitudes. We found that latitude, depth, substrate, and year were all important descriptors of fish and invertebrate diversity. Invertebrate richness and taxonomic diversity were highest at high latitudes and in deeper waters. Fish richness also increased with latitude, but exhibited a hump-shaped relationship with depth, increasing with depth up to the continental shelf break, ~200 m depth, and then decreasing in deeper waters. We found relationships between fish taxonomic and functional diversity and latitude, depth, substrate, and time at the regional scale, but not at the coast-wide scale, suggesting that coast-wide patterns can obscure important correlates at smaller scales. Our study provides insight into complex diversity patterns of the deep water soft substrate benthic ecosystems off the US West Coast

Growth rate of the kelp Saccharina sessilis​ under different wave conditions

Growth rate of the kelp <i>Saccharina sessilis</i> (C. Agardh Kuntze; previously <i>Hedophyllum sessile</i>) among different wave exposures. During June and July 2013, the growth rate of S. sessilis was measured using the hole punch method (Mann 1973 <i>Science</i>) at the rocky intertidal site at Fogarty Creek, Oregon USA (44.838N, -124.058W). Three locations within that site were measured as having low, intermediate, and highly wave exposed conditions (Barner et al. 2016 <i>Journal of Ecology</i>). Growth rate was measured by making a small hole punch in multiple kelps in the different wave-exposed areas, then returning within two weeks to measure growth. Each row in the data is an independent sample - a different individual kelp plant.<div><br></div><div><u>Original Question</u>: does growth rate of <i>S. sessilis</i> differ among wave exposures?<br><div><br></div><div><u>Variables in data (column headers)</u></div><div>Date: year_month_day</div><div>Exposure: L=low wave exposure, M=intermediate wave exposure, H = highly wave exposed</div><div>Length.to.hole: the length between the holdfast and the point at which the hole was initially punched (cm)</div><div>Growth: difference (in cm) between the original hole punch and the location of the punch after N days</div><div>When.punched?: date (year_month_day) that the growth measurement was taken</div><div>N.days: the number of days of growth</div><div>Growth.per.day: growth rate</div><div>Within tide-series?: was the growth measurement taken during a period of negative low tides or not (1 or 0)</div></div

Scaling and spatial patterns of species co-occurrence in a rocky intertidal meta-community

<p>Presentation from GRS Unifying Scales Across Ecology, July 2014 and from the Ecological Society of America meeting in August 2014<br></p

The missing theory of species co-occurrence in ecology

Talk for the "150 Years of <i>The American Naturalist</i>" Symposium at the 2018 Stand Alone Conference of the American Society of Naturalists.<br><br>Abstract: In 1983, <i>The American Naturalist</i> published a special issue, the innocuously titled “A Round Table on Research in Ecology and Evolutionary Biology.” Embedded in this broad title was an attempt to address a roiling debate in ecology at the time: can the spatial arrangement of species on a landscape be used to infer the underlying community structuring mechanism? Specifically, can co-occurrence patterns signal underlying competition? The seven papers in this issue magnify the surprisingly expansive questions at the heart of this debate through a profound exploration of ecology, evolution, inference, and philosophy. In recent years, similar competition-inference methods have resurfaced into prominence, as ecologists increasingly estimate species interactions using large databases of spatial and temporal occurrences. However, the important debates of the 20th century have been largely ignored in the rapid adoption and current widespread implementation of new machine learning and network inferential methods. Further, foundational concepts shaped through debate have significant bearing not only on the inference of species interactions, but also on the many pattern-process inference methods that dominate modern community assembly theory. In this symposium, I will trace the origins of the idea that species interactions can be inferred from spatial patterns, highlighting the role of this often-overlooked 1983 special issue. Further, I will explore the modern landscape of these debates about pattern-process inference, highlighting empirical ground-truthing, simulation models, and new theoretical frameworks

Mixed mating and demography in the sea palm kelp, Postelsia palmaeformis

<p>Presentation accompanying publication Barner et al. 2011, Proceedings of the Royal Society B. This version of the talk has been given as ~30 minute guest lecture to undergraduate science audience.</p