We are glad to welcome Emily Patterson to the lab! Emily will be joining the lab as an undergraduate in the Research Scholars Program in Insect Biology (RSPIB).
Vectors with autonomy: what distinguishes animal‐mediated nutrient transport from abiotic vectors?
Alexandra G. McInturf, Lea Pollack, Louie H. Yang and Orr Spiegel
Abstract
Animal movements are important drivers of nutrient redistribution that can affect primary productivity and biodiversity across various spatial scales. Recent work indicates that incorporating these movements into ecosystem models can enhance our ability to predict the spatio‐temporal distribution of nutrients. However, the role of animal behaviour in animal‐mediated nutrient transport (i.e. active subsidies) remains under‐explored. Here we review the current literature on active subsidies to show how the behaviour of active subsidy agents makes them both ecologically important and qualitatively distinct from abiotic processes (i.e. passive subsidies). We first propose that animal movement patterns can create similar ecological effects (i.e. press and pulse disturbances) in recipient ecosystems, which can be equal in magnitude to or greater than those of passive subsidies. We then highlight three key behavioural features distinguishing active subsidies. First, organisms can transport nutrients counter‐directionally to abiotic forces and potential energy gradients (e.g. upstream). Second, unlike passive subsidies, organisms respond to the patterns of nutrients that they generate. Third, animal agents interact with each other. The latter two features can form positive‐ or negative‐feedback loops, creating patterns in space or time that can reinforce nutrient hotspots in places of mass aggregations and/or create lasting impacts within ecosystems. Because human‐driven changes can affect both the space‐use of active subsidy species and their composition at both population (i.e. individual variation) and community levels (i.e. species interactions), predicting patterns in nutrient flows under future modified environmental conditions depends on understanding the behavioural mechanisms that underlie active subsidies and variation among agents’ contributions. We conclude by advocating for the integration of animal behaviour, animal movement data, and individual variation into future conservation efforts in order to provide more accurate and realistic assessments of changing ecosystem function.
Biological Reviews
Welcome, Tracie!
We are very excited that Tracie Hayes will be joining the lab this year! Tracie recently received an NSF Graduate Research Fellowship, and will be a Ph.D. student in the Population Biology Graduate Group starting in the fall. Yay!
The effects of pulsed fertilization and chronic herbivory by periodical cicadas on tree growth
Louie H. Yang and Richard Karban
Abstract
While many studies have investigated plant growth in the context of episodic herbivory and pressed resource availability, relatively few have examined how plant growth is affected by pulsed resources and chronic herbivory. Periodical cicadas (Magicicada spp.) adults represent a pulsed detrital subsidy that fertilizes plants, while live cicada nymphs are long-lived root-feeding herbivores. Previous studies of cicada herbivory effects have been inconclusive, and previous studies of cicada-mediated fertilization did not examine effects on trees, or on a multi-year timescale. Here we describe the results of a three-year experiment that factorially manipulated the presence and absence of cicada fertilization and herbivory in a population of 100 American sycamore (Platanus occidentalis) trees. We found that cicada fertilization strongly increased tree growth in the year of emergence, creating differences in tree size that persisted at least two years later. By comparison, we did not detect reductions in tree growth associated with cicada herbivory in any year of this experiment. However, cicada herbivory reduced the densities of, and damage from, other aboveground herbivores. These results suggest that cicadas affect the size structure of forests over multiple years, and raise questions about how cicada-mediated fertilization and herbivory will affect tree growth over longer timescales.
Ecology
Seasonal assembly of arthropod communities on milkweeds experiencing simulated herbivory
Ian Pearse, Marshall McMunn, and Louie H. Yang
Abstract
The seasonal assembly of arthropod communities is shaped by biotic and abiotic aspects of the habitat that limit the appearance or activity phenology of potential community members. In addition, previous interactions within the community, such as herbivore-induced plant defensive responses, aggregation, and predator avoidance likely affect the assembly of arthropod communities on individual plants. We observed the phenology of arthropod communities and defensive plant traits on 100 milkweed (Asclepias eriocarpa) individuals at monthly intervals over a growing season. We experimentally wounded a subset of plants each month (April–August) to observe the effect of simulated added herbivore damage on the seasonal assembly of these arthropod communities. All plant traits and measures of arthropod communities changed over the season. The observed response to experimental leaf damage suggested a trend of induced susceptibility in early months, but not late months. Plants receiving early-season simulated herbivory experienced more subsequent leaf damage than unmanipulated plants. We observed several lagged correlations in our study indicating that blue milkweed beetle (Chrysochus cobaltinus) abundance was lower in months following high natural leaf damage, and that the abundance of a secondary omnivore (Lygaeus kalmii) and total predator abundance tended to follow months with high C. cobaltinus abundance. Ahistorical habitat factors determined much of the observed seasonality of arthropod communities, but induced responses to simulated herbivory also contributed historical effects that influenced arthropod community assembly.
Arthropod-Plant Interactions. 13:99–108
The mechanisms of phenology: the patterns and processes of phenological shifts
Helen E. Chmura, Heather M. Kharouba, Jaime Ashander, Sean M. Ehlman, Emily B. Rivest and Louie H. Yang
Abstract
Species across a wide‐range of taxa and habitats are shifting phenological events in response to climate change. While advances are common, shifts vary in magnitude and direction within and among species, and the basis for this variation is relatively unknown. We examine previously suggested patterns of variation in phenological shifts in order to understand the cue‐response mechanisms that underlie phenological change. Here, we review what is known about the mechanistic basis for nine factors proposed to predict phenological change (latitude, elevation, habitat type, trophic level, migratory strategy, ecological specialization, species’ seasonality, thermoregulatory mode, and generation time). We find that many studies either do not identify a specific underlying mechanism or do not evaluate alternative mechanistic hypotheses, limiting the ability of scientists to predict future responses to global change with accuracy. We present a conceptual framework that emphasizes a critical distinction between environmental (cue‐driven) and organismal (response‐driven) mechanisms causing variation in phenological shifts and discuss how this distinction can reduce confusion in the field and improve predictions of future phenological change.
Ecological Monographs
2019 Experimental Ecology and Evolution in the Field (EVE/ENT 180 A/B)
Winter and Spring 2019
What is it? A 2-quarter field course focused on a single research project.
Why should I take it? Past students have said:
“There is no other course on campus that promotes such a high level of independent thinking as well as cooperative work. By far, one of the best and most unique courses available at UC Davis.”
“Let me be clear. I have learned more, developed more as an ecologist, and experienced more valuable lessons in the past 6 months than in the entirety of the past 3 years. This class is how college is meant to be taught!”
“Probably the best course I have taken at Davis. I learned so much; even though it is a lot of work, truly the best way to learn is through hands on experience, which this class definitely provided!”
“EVE 180 is such a great class. It has really influenced the way I view experiments and the scientific method. The stuff I learned in this class will help me in grad school and beyond. Favorite class I’ve ever taken for sure.”
“The hands on approach of this course has been vital to understanding the process of science. After this course, I feel I really know what I am in for in my future career.”
What else do I need to know? The prerequisites are incorrect on Schedule Builder. The correct prerequisites are: EVE 100 + (ENT 105 or ESP 100 or EVE 101). Due to the unusual nature of this course, all prospective students are strongly encouraged to contact the instructor (Louie H. Yang, lhyang@ucdavis.edu).
Welcome, Elizabeth!
Elizabeth Postema arrived on campus for her first day of grad school today! We got her some keys, did a little safety orientation, and scheduled our weekly lab meeting. And so it begins…
Experimental shifts in phenology affect fitness, foraging, and parasitism in a native solitary bee
Shahla Farzan and Louie H. Yang
Abstract
Phenological shifts have been observed in a wide range of taxa, but the fitness consequences of these shifts are largely unknown, and we often lack experimental studies to assess their population‐level and evolutionary consequences. Here, we describe an experimental study to determine the fitness consequences of phenological shifts in blue orchard bee (Osmia lignaria) emergence, compare the measured seasonal fitness landscape with observed phenology in the unmanipulated population, and assess seasonal variation in key factors related to reproduction, foraging, and brood parasitism that were expected to affect the shape of the fitness landscape. By tracking individually marked females, we were able to estimate the lifetime fitness impacts of phenological advances and delays. We also measured parasitism risk, floral resource use, and nesting behavior to understand how each varies seasonally, and their combined effects on realized fitness. Survival to nesting decreased non‐monotonically throughout the season, with a 20.4% decline in survival rates between the first and second cohorts. The total reproductive output per maternal bee was 14.9% higher in the second cohort compared the first, and 161% higher in the second cohort compared to the third. Combining seasonal patterns in survival and reproductive output, experimentally advanced females showed 30.6% higher fitness than bees released at the historic peak. In contrast, the nesting phenology of unmanipulated bees showed nearly equal numbers of nesting attempts in the first two cohorts. Both increased resource availability and reduced parasitism risk favored earlier emergence. These results are consistent with a population experiencing directional selection for earlier emergence, adaptive bet‐hedging, or developmental constraints. Our study offers insight into the fitness consequences of phenological shifts, the mechanisms affecting the fitness consequences of phenological shifts in a community context, and the potential for adaptive responses to climate change.
Ecology; Accepted Articles; July 31, 2018
Marshall McMunn receives an NSF Postdoctoral Fellowship in Biology
Marshall McMunn received a 2018 NSF Postdoctoral Fellowship in Biology for his proposal to examine how temperature change affects bacteria that live within the gut of a desert ant. His abstract says, “Many animal guts contain bacteria that aid in digestion, but the bacteria within Cephalotes rohweri (the Arizona turtle ant) are unusual in two important ways 1) the bacteria help the ant acquire nitrogen, a key nutrient in growth and development, and 2) the bacteria survive extremely hot temperatures. The fellow will perform several experiments to determine if this bacterial community provides benefits to its ant host despite extreme heat exposure. The research improves scientific understanding of how animals can cope with a changing environment through shifts in their bacterial partners. The research broadly informs current industrial and commercial efforts to manipulate bacteria associated with animals and plants to improve food production. As a part of this research the fellow will develop a set of software tools to enable visually impaired scientists to interact with data through the sense of touch.” Marshall will be advised in this postdoc by Stacy Philpott (UC Santa Cruz) and Rachel Vanette (UC Davis).