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


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,

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


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).


The Yang Lab 2.0

Hello, world. This is the new Yang Lab website, updated for the first time since 2009. Back then, I spent a couple weeks over the holidays learning how to cobble together some Dreamweaver HTML, Flash and Spry elements in order to represent our lab to the world. Since then, the lab has changed, the world has changed and web design has changed. So, we were long overdue for an updated website.

Our new lab website is simpler, and I hope it will be easier for me to keep it up-to-date, and to have other folks in the lab contribute as well. We are using a content management system this time around. While I had to give up the joy of hacking whatever I want into the code, I think we gain a lot. Hello, world! The times they are a-changing.

Global shifts in the phenological synchrony of species interactions over recent decades

Heather M. KharoubaJohan EhrlénAndrew GelmanKjell BolmgrenJenica M. AllenSteve E. Travers, and Elizabeth M. Wolkovich


Phenological responses to climate change (e.g., earlier leaf-out or egg hatch date) are now well documented and clearly linked to rising temperatures in recent decades. Such shifts in the phenologies of interacting species may lead to shifts in their synchrony, with cascading community and ecosystem consequences. To date, single-system studies have provided no clear picture, either finding synchrony shifts may be extremely prevalent [Mayor SJ, et al. (2017) Sci Rep 7:1902] or relatively uncommon [Iler AM, et al. (2013) Glob Chang Biol 19:2348–2359], suggesting that shifts toward asynchrony may be infrequent. A meta-analytic approach would provide insights into global trends and how they are linked to climate change. We compared phenological shifts among pairwise species interactions (e.g., predator–prey) using published long-term time-series data of phenological events from aquatic and terrestrial ecosystems across four continents since 1951 to determine whether recent climate change has led to overall shifts in synchrony. We show that the relative timing of key life cycle events of interacting species has changed significantly over the past 35 years. Further, by comparing the period before major climate change (pre-1980s) and after, we show that estimated changes in phenology and synchrony are greater in recent decades. However, there has been no consistent trend in the direction of these changes. Our findings show that there have been shifts in the timing of interacting species in recent decades; the next challenges are to improve our ability to predict the direction of change and understand the full consequences for communities and ecosystems.

Meredith Cenzer receives 2018 American Naturalist Student Paper Award

Meredith Cenzer received the 2018 American Naturalist Student Paper Award for her impressive paper “Maladaptive Plasticity Masks the Effects of Natural Selection in the Red-Shouldered Soapberry Bug” (Am Nat 190:521-533). The award committee said, “In this work, Dr. Cenzer leveraged a unique opportunity to quantify maladaptive plasticity and explore its consequences; she designed and executed difficult experiments and capitalized on an unexpected result to draw big and convincing conclusions. We particularly appreciated how her study incorporates measures of selection, population effects (presumably genetic), and common-garden rearing to quantify plasticity. We found her paper to be an elegant combination of ecology, evolution, behavior, and natural history. While it focuses on a single system, maladaptive plasticity is so rarely investigated that we became convinced that hers will come to be considered a landmark study. It is particularly sophisticated work for a single-authored graduate student publication. (Read her summary here:”