The Huck Institutes of the Life Sciences

Ecology Colloquium schedule

Upcoming talks in Ecology 590, the Graduate Colloquium
Schedule and Talk Summaries for Fall 2017 Ecology Graduate Colloquium (ECLGY 590)
Wednesday 12:20 – 1:10 PM, 104 Forest Resources Building





 Aug 30

 No Colloquium


 Sep 6

 No Colloquium



 No Colloquium


 Sep 20

 Erynn Maynard

Novel leaf phenology of invasive shrubs across eastern U.S. forests

 Sep 27

 No Colloquium


 Oct 4

 Lake Graboski

Oak and red maple regeneration in central Pennsylvania

 Oct 11

 Vishnupriya  Sankararaman

Producing diversity: agroforests sustain avian richness and abundance in India's Western Ghats

 Oct 18

 Braulio De Almeida Assis

Relationships between ornamentation on female lizards and offspring survival, growth rate and immune function.

 Oct 25

 Carli Dinsmore

Modeling growth variability in the ectotherm Thamnophis elegans

 Nov 1

 Courtney Davis

Refining parameter estimation and computational efficiency in studies of population and community ecology

 Nov 8

 Ellen Brandell

Understanding the consequences of disease in a social carnivore

 Nov 15

 Sarah Isbell

Interseeded cover crops: Evaluating nitrogen retention services provided by plant- microbe relationships in agroecosystems

 Nov 22

 Thanksgiving Break

 Nov 29

 Andie Chan

Differential responses of a facultatively symbiotic coral (Astrangia poculata) and its algal symbiont (Symbiodinium psygmophilum) to thermal stress

 Dec 6

 Dustin Owen

Effects of maternal stress on lizard heart rate



Fall 2017 Ecology Colloquium Summaries


Sept. 20.  Erynn Maynard. Novel leaf phenology of invasive shrubs across eastern U.S. forests 

Invasive shrubs are a major concern in eastern U.S. forests where their success is at the cost of native species diversity and tree regeneration. One of the reasons for this success may be an extended period with leaves for invasive shrubs compared to native woody species. An earlier leaf emergence in the spring and a later leaf drop in the fall allows invasive shrubs to take advantage of greater light infiltration when many canopy trees don’t have leaves. Furthermore, extended leaf phenology (ELP) of invasive shrubs creates novel shade when native understory species are adapted for seasonally brighter conditions. Despite widespread anecdotal observations, there are surprisingly few studies quantifying ELP of invasive shrubs and the environmental cues that drive the novel phenology. I have a series of ongoing research projects in central Pennsylvania showing ELP in the spring and fall for numerous invasive shrub species. The limited spatial extent of these data make it difficult to identify cues like temperature that drive leaf phenology and that vary from region to region. So, we don’t know if the differences and impacts we observe in central PA are equivalent to the differences in other parts of the invaded range. Consequently, I initiated a citizen science campaign with the National Phenology Network called Shady Invaders. Participants collect data on leaf phenology from across the eastern U.S. I will present some preliminary models developed from this regional dataset. Beyond a better understanding of the cues that drive differences in leaf phenology, we could use such models to predict where ELP may be lesser or greater, providing insight into invasion dynamics and facilitating targeted invasive management.


Oct 4.  Lake Graboski.  Oak and red maple regeneration in central Pennsylvania

My thesis proposal takes a new look at regeneration ecology of oak species and red maple with the newest data from the Oak Regeneration Study in Pennsylvania, a long term observational study on forest regeneration in oak-dominant forests. My goal is to improve upon existing knowledge through model-based inference.


Oct 11. Vishnupriya Sankararaman.  Producing diversity: agroforests sustain avian richness and abundance in India's Western Ghats

Globally, protected areas have long been the corner stone of biodiversity conservation efforts. In India’s Western Ghats, small and isolated protected areas are embedded in a matrix of multiple land-uses, most of which include agroforests. These agroforests are being increasingly recognized for their supplementary role in conserving wildlife. To test the efficacy of this, we examined bird species richness and densities across areca, coffee and rubber agroforests in the Western Ghats. We carried out point-count surveys in 187 agroforests across a 29,634 km2 area of the Ghats. Results demonstrated that coffee supported higher species richness, and densities in all four habitat guilds and three of four feeding guilds compared to areca and rubber. Species richness was modelled as a function of important biogeographic and environmental covariates. The most influential factors were tree cover, tree density and rainfall in all agroforests, and the relative strength of these effects varied. Overall we found that all three agroforests do play a role in providing subsidiary habitats for birds in the Ghats.


Oct 18.  Braulio De Almeida Assis.  Relationships between ornamentation on female lizards and offspring survival, growth rate and immune function.

Female fence lizards vary in the color intensity of sexual badges found on their necks and abdomen. Offspring of females with more saturated badges were less likely to survive to maturity, and the ones who did survive exhibited reduced mass gain and increased immune response. The mechanisms behind these relationships remain to be explored, but androgen levels of offspring and their mothers constitute an important avenue for future investigation.


Oct. 25.  Carli Dinsmore.  Modeling growth variability in the ectotherm Thamnophis elegans

Individual variability in growth rate has important implications for adaptive plasticity and the evolution of growth trajectories. Optimization models show that overall fitness is positively correlated with body size, through life-history traits including longevity, age and size at maturity and life-time reproductive output. Growth rate constitutes a link between resource acquisition and partitioning with asymptotic body size. The purpose of my study is to assess environmental components and reproductive trade-offs which lead to variation in growth rate between the sexes, across time and among and between populations and cohorts. Measuring growth in wild populations of vertebrates presents a significant challenge, since observations depend on if and when animals can be recaptured to measure growth.

Using Bayesian methods I will fit capture-mark-recapture data from a long-term study of Western terrestrial garter snakes, Thamnophis elegans. The data come from a > 40-year study of garter snake populations in the Lassen National Forest. My goal is to determine whether populations that vary greatly in stability of food resource availability respond differently to annual climatic variation. Using both length-at-first capture and age-at-first capture parameterizations, I will fit individual-specific curves of the von Bertalanffy growth model. I will use this approach to determine how annual and cohort differences in rainfall (a determinant of food availability) affect growth rate and asymptotic size in low and high resource variable populations.


Nov. 1.  Courtney Davis.   Refining parameter estimation and computational efficiency in studies of population and community ecology

With recent efforts to coordinate, consolidate and integrate ecological data from various ecosystems across large temporal and spatial scales, there is a huge demand for efficient yet effective statistical tools. I propose three methods – variational approximations, structural equation models, and integrated population models – to improve parameter estimation and computational efficiency in studies of population- and community-level responses to environmental change.  Each of these methods can be used to link large-scale ecosystem drivers to local community dynamics while accounting observational uncertainty. In brief, variational approximations are an efficient alternative to other estimation methods, such as MCMC (Markov Chain Monte Carlo), that allow for inference on statistically complex models. The development and application of accessible variational methods could allow for efficient parameter estimation when it is otherwise unwieldy or even impossible. Furthermore, our current understanding of species and community responses to environmental change is limited by our ability to adequately quantify: 1) interspecific interactions, 2) interactions between communities and the physical environment in which they occur, and 3) interactions between the physical environment and macro-ecosystem drivers, such as climate. Structural equation modeling can improve our understanding by providing a mechanistic representation of how species interact with their environment and with other species. This flexible framework allows hypotheses regarding cause-effect relationships to be tested, providing a method by which direct and indirect effects – and the strength of those effects – on the response variable(s) of interest can be quantified. Integrated population models can also improve our understanding of these interactions by combining independent data sources (e.g., capture-recapture data and survey data) to more accurately estimate demographic processes at large temporal and spatial scales. In doing so, integrated models improve our ability to predict system responses to large-scale disturbances, such as environmental change. Nevertheless, these three methods have been limited in their application to ecological studies for a variety of reasons.  My proposed research will further develop the utility and accessibility of these methods, such that other ecologists can use these tools to better understand population- and community-level responses to variable environments and changing conditions.


Nov. 8.  Ellen Brandell. Understanding the consequences of disease in a social carnivore.

Trophic interactions and disease in social species have become an increasingly popular research topics in the past few decades, yet there is a lack of integration between the two. Disease is ubiquitous in wild animal communities and can have devastating impacts on populations at all trophic levels. Thus, the need to understand how disease fits into the food web is crucial for deciphering and predicting how the food web will respond to perturbations. Here, I will be proposing my Doctoral research, aimed at uncovering how disease in both a social, apex predator and its main prey species affects predator-prey interactions.


Nov. 15.  Sarah Isbell.  Interseeded cover crops: Evaluating nitrogen retention services provided by plant- microbe relationships in agroecosystems

Can we use ecological concepts to understand, predict, and improve how organic agricultural systems perform? Organic cropping systems that incorporate cover crops exhibit considerable ecological complexity, resulting in potential agronomic benefits and challenges. Nitrogen (N) management is a critical challenge, as nitrate leaching is not only a source of pollution affecting waterways, air quality, and biodiversity, but also represents an economic loss for farmers. Two ongoing experiments in Pennsylvania are evaluating the strategy of interseeding a cover crop into a standing corn crop. This approach increases the ecological complexity of the system by using nutrient and light competition and partitioning to reduce weeds and leaching losses. However, it is not yet clear how this strategy will impact soil, plant, and microbial N pools. This presentation will use data collected from 2015-2017 to explore tradeoffs in N management between an interseeded cover cropping system and other standard practice organic corn cropping systems.


Nov 29.  Andie Chan.  Differential responses of a facultatively symbiotic coral (Astrangia poculata) and its algal symbiont (Symbiodinium psygmophilum) to thermal stress

The potential for sessile species to survive climate change depends in part on their ability to acclimatize to warming. While tropical corals exist within a narrow temperature profile, the scleractinian northern star coral, Astrangia poculata, extends over 11 degrees of latitude. Colonies of A. poculata are facultatively symbiotic, which provides a unique system for studying the coral host with and without the dinoflagellate Symbiodinium psygmophilum. Eight colonies of A. poculata were collected from Naragansett Bay, Rhode Island, and fragmented into four pieces. Genetically identical symbiotic and aposymbiotic fragments were exposed to increased temperatures for three weeks. Maximum photochemical efficiency (Fv/Fm) was measured daily throughout the ramping period from 18 to 30°C, and during the hold at 30°C. Respiration, photosynthesis, and reflectance were measured every three days. Finally, RNA was extracted from all fragments and submitted for RNAseq analysis. While some host and symbiont genotype combinations maintained a steady metabolic rate despite extreme temperatures, others elevated their respiration rates. No colony death was observed, thus indicating that A. poculata colonies from the northern edge of this species’ range are able to acclimatize to temperatures consistent with the southern edge. There was an overall decrease in photochemistry (Fv/Fm) and in the maximum photosynthetic rates (Pmax) in the symbiotic colonies that were exposed to extreme high temperatures, showing a stress response in the algae. These results demonstrate that the thermal tolerance of the coral host and symbiont differ, and that considering both is important when predicting how climate change will affect this species.


Dec 6.   Dustin A.S. Owen.  Effects of Maternal Stress on Lizard Heart Rate

Recently in vertebrates, maternally-derived stress hormones, glucocorticoids, have been shown as a significant inducer of transgenerational phenotypic plasticity. Offspring phenotypic responses are often interpreted as unavoidable negative side effects of maternal stress. Growing evidence supports the adaptive hypothesis for maternal stress whereby phenotypic responses in offspring may be adaptively matched to the local environment. While many studies have examined how maternal stress has influenced the post-natal trails of offspring, few studies have addressed the effects of maternal stress on the pre-natal life stage. We tested the hypothesis that stressed female eastern fence lizards (Sceloporus undulatus) and their offspring have higher metabolic rates (i.e. heart rates). This could result in faster growth, and increased respiratory capacity to facility survival in a stressful environment.