Freshwater crabs are macroconsumers that are commonly found in Neotropical headwater streams that may play a key role in energy flow and nutrient cycling in detrital food webs. Although studies have examined the feeding habits of trichodactylid crabs, little is known of this behavior in pseudothelphusid species, and specifically whether they actually consume leaf material. We conducted three nine-day laboratory trials with pseudothelphusid crabs (Ptychophallus tumimanus (Rathbun, 1898)) and leaves (Koanophyllon pittieri) to investigate whether crabs shred leaves. We hypothesized that leaf mass loss would be faster with crabs present relative to control tanks with only leaves. Leaf mass loss was significantly higher (p < 0.001) in tanks with crabs (0.49 ± 0.07 g, mean ± 1 SD) compared to control tanks (0.31 ± 0.05 g). We observed crabs manipulating, shredding, and consuming leaves, with leaf fragments and egesta present in tanks with crabs but not in control tanks. Their consumption and egestion activity may affect nutrient availability and transformation by stimulating microbial activity during leaf breakdown and converting coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM). Therefore, freshwater crabs need to be considered when studying energy flow and nutrient cycling in detrital food webs of Neotropical headwater streams.
Wild animals commonly experience trade-offs in their investment among different physiological processes, including reproduction, nutrition, and immune function. In particular, given its importance for pathogen defense, many studies have sought to measure when and why animals modulate their investment in immunity. However, since animals encounter a range of conditions in natural environments, the observation of these physiological trade-offs are likely shaped by a variety of intrinsic and extrinsic factors.
Through her masters thesis research, Ashley explored such context-dependence in immune dynamics. In her first chapter, she examined variation in relationships between testosterone and immunity in free-ranging American alligators, finding that the effects of testosterone on microbial killing depended on levels of co-circulating hormones, the microbe of interest, and temperature. In her second chapter, Ashley further explored relationships between immune performance and temperature across vertebrate species, finding that the effects of temperature on immune performance depended on host thermoregulation strategy. For example, ectotherms experienced trade-offs between immune performance at the host’s optimal temperature and the consistency of immune performance across temperatures, but these trade-offs were absent in endotherms. Together, Ashley’s work emphasizes the importance of considering both intrinsic and extrinsic variation when assessing the immune performance of wild vertebrates. Importantly, accounting for this context-dependence will be crucial in understanding the relevance of physiological trade-offs across animal systems.
Kate Sabey, a PhD Candidate in the Ezenwa Lab and an IDEAS Trainee, was selected as a P.E.O. Scholar. Kate’s research focuses on the relationship between the gut microbiome and infection status of wild African ungulates, using disease ecology and genomic approaches. After completing her dissertation work through the Department of Infectious Diseases, Kate will proceed with veterinary medicine training as part of her dual DVM-PhD degree. Well done, Kate!
During the week of June 1st, EcoReach participated in the inaugural #BlackBirdersWeek on social media, which Kaylee Arnold co-organized. This movement was started by @BlackAFinSTEM on Twitter in response to the video of a white woman who called the police on birdwatcher (or “birder”) Christian Cooper after he requested that she follow regulations and leash her dog in Central Park. As America continues to grapple with systemic racism and violence following the deaths of Ahmaud Arbery, Breonna Taylor, George Floyd, Tony McDade, Nina Pop, and so many others, it has also been highlighted that Black people face unique challenges and discrimination in the field of Ecology or when out in nature, even while doing something as simple as bird watching or going outside for a jog.
Inspired by these events, EcoReach and other OSE members teamed up with Lilly Branch Audubon Society to support the Oconee Rivers Audubon Society’s “Binoculars for Young Black Birders,” a binoculars drive to support young, Black birders in Athens-Clarke County. In just under a few weeks, we raised nearly $20,000 from GoFundMe donations and direct donations to Oconee Rivers Audubon Society (ORAS). With this money, EcoReach is currently working with Clarke County School District (CCSD) to provide individual binoculars and local bird guides to every K-12 Black student in CCSD that would like a pair as well as provide additional binoculars and guides to each CCSD science teacher to use in their classrooms. Lack of access to equipment, such as binoculars, results in substantial inequitable access to outdoor activities and outdoor education. By providing students with their own binoculars and field guides, we can help remove one of the many barriers Black students may face in regards to participating in outdoor activities that so many of us enjoy and take for granted.
The majority of terrestrial net primary production decomposes, fueling detrital food webs and converting dead plant carbon to atmospheric CO 2. There is considerable interest in determining the sensitivity of this process to climate warming. A common approach has been to use spatial gradients in temperature (i.e., latitude or elevation) to estimate temperature sensitivity. However, these studies typically relate decomposition rates to average temperatures at each site along such gradients, ignoring within‐site temperature variation. To evaluate the potential effects of temperature variation on estimates of temperature sensitivity, we simulated plant litter decomposition using both randomly generated and real time series of temperature. This simulation approach illustrated how temperature variation leads to higher decomposition rates at a given mean temperature than is predicted from simulations in which temperature is held constant. Increases in decomposition rate were most evident at cooler sites, where temporal variation in temperature tends to be greater than at warmer sites. This unbalanced effect of temperature variation shifted the slope of the relationships between average temperature and decomposition rate, resulting in lower estimated temperature sensitivities than were used to simulate decomposition. For example, estimates of activation energy (E a) were as much as 0.15 eV lower than the true E a when decomposition was simulated with the true E a set to the canonical respiration value of 0.65 eV . We found that the estimated E a was lower than the true E a for surface, soil, and air temperatures, but not for stream temperatures, for which there was only a weak relationship between temperature variation and mean temperature. Our results suggest that commonly used methods may underestimate the temperature dependence of litter decomposition, particularly in terrestrial environments. We encourage publication of temperature data that include variation estimates and suggest an alternative method for calculating temperature sensitivity that accounts for variation in temperature.
Tomczyk NJ, Rosemond AD, Bumpers PM, Cummins CS, Wenger SJ, Benstead JP. Ignoring temperature variation leads to underestimation of the temperature sensitivity of plant litter decomposition. Ecosphere. 2020 Feb;11(2):e03050. doi: 10.1002/ecs2.3050.
Emily Bertucci is the inaugural recipient of the new Dr. Rebecca Reyburn Sharitz and Carl Byrne Hatfield Fellowship. Emily, advised by Dr. Ben Parrott, is researching the proximate mechanisms that produce variation in biological aging – specifically, epigenetic changes that occur with age and how normal age-related changes are impacted by exposures to stressful environments. This year, she is investigating how exposures to stress during sensitive life stages alters the epigenome and produces variation in aging and life history traits at the individual and population levels.
Spatial synchrony—correlated abundance fluctuations among distinct populations—is associated with increased extinction risk but is not a component of widely-used extinction risk assessments (e.g., IUCN Red List, U.S. Fish and Wildlife Service’s Species Status Assessment). Alongside traditional viability metrics (i.e., the number of populations, their spatial extent, the status of each population), consideration of spatial synchrony in these assessments may provide additional insight into extinction risk as well as the relative importance of intrinsic and extrinsic factors on population dynamics. We demonstrate a method for estimating abundance trends in populations of the endangered freshwater fish, the amber darter (Percina antesella), while simultaneously assessing empirical support for existence of spatial synchrony among its two populations in the Conasauga and Etowah rivers in Georgia, U.S.A. Our analysis was performed using multivariate autoregressive state-space (MARSS) models with annual sampling data from 1996 to 2018 at 16 sites distributed between the two rivers. Our results indicate that amber darter populations have declined substantially, with 9% annual losses in both the Conasauga and Etowah rivers, suggesting rangewide imperilment. Furthermore, model selection indicated little support for models with fully independent dynamics between rivers, which may compound overall extinction risk. This analysis demonstrates the utility of tools such as MARSS models for assessing spatial synchrony and long-term population trajectories of imperiled species, resulting in improved vulnerability assessments that do not assume independence among separate populations.
Stowe, E.S., Wenger, S.J., Freeman, M.C. and Freeman, B.J., 2020. Incorporating spatial synchrony in the status assessment of a threatened species with multivariate analysis. Biological Conservation, 248, p.108612. doi: 10.1016/j.biocon.2020.108612
Species displaying temperature-dependent sex determination (TSD) are especially vulnerable to the effects of a rapidly changing global climate due to their profound sensitivity to thermal cues during development. Predicting the consequences of climate change for these species, including skewed offspring sex ratios, depends on understanding how climatic factors interface with features of maternal nesting behaviour to shape the developmental environment. Here, we measure thermal profiles in 86 nests at two geographically distinct sites in the northern and southern regions of the American alligator’s (Alligator mississippiensis) geographical range, and examine the influence of both climatic factors and maternally driven nest characteristics on nest temperature variation. Changes in daily maximum air temperatures drive annual trends in nest temperatures, while variation in individual nest temperatures is also related to local habitat factors and microclimate characteristics. Without any compensatory nesting behaviours, nest temperatures are projected to increase by 1.6–3.7°C by the year 2100, and these changes are predicted to have dramatic consequences for offspring sex ratios. Exact sex ratio outcomes vary widely depending on site and emission scenario as a function of the unique temperature-by-sex reaction norm exhibited by all crocodilians. By revealing the ecological drivers of nest temperature variation in the American alligator, this study provides important insights into the potential consequences of climate change for crocodilian species, many of which are already threatened by extinction.
Bock SL, Lowers RH, Rainwater TR, Stolen E, Drake JM, Wilkinson PM, Weiss S, Back B, Guillette Jr L, Parrott BB. Spatial and temporal variation in nest temperatures forecasts sex ratio skews in a crocodilian with environmental sex determination. Proceedings of the Royal Society B. 2020 May 13;287(1926): 20200210.
Understanding the drivers of biodiversity is important for forecasting changes in the distribution of life on earth. However, most studies of biodiversity are limited by uneven sampling effort, with some regions or taxa better sampled than others. Numerous methods have been developed to account for differences in sampling effort, but most methods were developed for systematic surveys in which all study units are sampled using the same design and assemblages are sampled randomly. Databases compiled from multiple sources, such as from the literature, often violate these assumptions because they are composed of studies that vary widely in their goals and methods. Here, we compared the performance of several popular methods for estimating parasite diversity based on a large and widely used parasite database, the Global Mammal Parasite Database (GMPD). We created artificial datasets of host–parasite interactions based on the structure of the GMPD, then used these datasets to evaluate which methods best control for differential sampling effort. We evaluated the precision and bias of seven methods, including species accumulation and nonparametric diversity estimators, compared to analyzing the raw data without controlling for sampling variation. We find that nonparametric estimators, and particularly the Chao2 and second‐order jackknife estimators, perform better than other methods. However, these estimators still perform poorly relative to systematic sampling, and effect sizes should be interpreted with caution because they tend to be lower than actual effect sizes. Overall, these estimators are more effective in comparative studies than for producing true estimates of diversity. We make recommendations for future sampling strategies and statistical methods that would improve estimates of global parasite diversity.
Also highlighted on UGA’s Center for the Ecology of Infectious Disease website.
Teitelbaum, C.S., Amoroso, C.R., Huang, S., Davies, T.J., Rushmore, J., Drake, J.M., Stephens, P.R., Byers, J.E., Majewska, A.A. and Nunn, C.L. (2020), A comparison of diversity estimators applied to a database of host–parasite associations. Ecography. doi:10.1111/ecog.05143