Leslie Ries

A PREDICTIVE MODEL OF EDGE EFFECTS

Edge effects are among the most extensively studied ecological phenomena, yet we lack a general, predictive framework to understand the patterns and variability observed. We present a conceptual model, based on resource distribution, that predicts whether organismal abundances near edges are expected to increase, decrease, or remain unchanged for any species at any edge type. Predictions are based on whether resources are found predominantly in one habitat (decreased abundance in preferred habitat, increase in non-preferred), divided between habitats (predicts an increase near both edges), spread equally among habitats (predicts a neutral edge response), or concentrated along the edge (increase). There are several implications of this model that can explain much of the variability reported in the edge literature. For instance, our model predicts that a species may show positive, negative, and neutral responses, depending on the edge type encountered, which explains some intraspecific variability observed ...

Habitat edges as a potential ecological trap for an insect predator

Abstract.  1. Ecological traps, where animals actively select poor habitat for reproduction over superior habitat, are generally associated with birds at forest edges. This study examines oviposition preference, predation, and parasitism rates in the mantid Stagmomantis limbata to determine the potential generality of this phenomenon.

Reproductive asynchrony in natural butterfly populations and its consequences for female matelessness.

1. Reproductive asynchrony, where individuals in a population are short-lived relative to the population-level reproductive period, has been identified recently as a theoretical mechanism of the Allee effect that could operate in diverse plant and insect species. The degree to which this effect impinges on the growth potential of natural populations is not yet well understood. 2. Building on previous models of reproductive timing, we develop a general framework that allows a detailed, quantitative examination of the reproductive potential lost to asynchrony in small natural populations. 3. Our framework includes a range of biologically plausible submodels that allow details of mating biology of different species to be incorporated into the basic reproductive timing model. 4. We tailor the parameter estimation methods of the full model (basic model plus mating biology submodels) to take full advantage of data from detailed field studies of two species of Parnassius butterflies whose mating status may be assessed easily in the field. 5. We demonstrate that for both species, a substantial portion of the female population (6.5-18.6%) is expected to die unmated. These analyses provide the first direct, quantitative evidence of female reproductive failure due to asynchrony in small natural populations, and suggest that reproductive asynchrony exerts a strong and largely unappreciated influence on the population dynamics of these butterflies and other species with similarly asynchronous reproductive phenology.

Tracking climate impacts on the migratory monarch butterfly

Understanding the impacts of climate on migratory species is complicated by the fact that these species travel through several climates that may be changing in diverse ways throughout their complete migratory cycle. Most studies are not designed to tease out the direct and indirect effects of climate at various stages along the migration route. We assess the impacts of spring and summer climate conditions on breeding monarch butterflies, a species that completes its annual migration cycle over several generations. No single, broad-scale climate metric can explain summer breeding phenology or the substantial year-to-year fluctuations observed in population abundances. As such, we built a Poisson regression model to help explain annual arrival times and abundances in the Midwestern United States. We incorporated the climate conditions experienced both during a spring migration/breeding phase in Texas as well as during subsequent arrival and breeding during the main recruitment period in Ohio. Using data from a state-wide butterfly monitoring network in Ohio, our results suggest that climate acts in conflicting ways during the spring and summer seasons. High spring precipitation in Texas is associated with the largest annual population growth in Ohio and the earliest arrival to the summer breeding ground, as are intermediate spring temperatures in Texas. On the other hand, the timing of monarch arrivals to the summer breeding grounds is not affected by climate conditions within Ohio. Once in Ohio for summer breeding, precipitation has minimal impacts on overall abundances, whereas warmer summer temperatures are generally associated with the highest expected abundances, yet this effect is mitigated by the average seasonal temperature of each location in that the warmest sites receive no benefit of above average summer temperatures. Our results highlight the complex relationship between climate and performance for a migrating species and suggest that attempts to understand how monarchs will be affected by future climate conditions will be challenging.

A rare model limits the distribution of its more common mimic: a twist on frequency-dependent Batesian mimicry.

Abstract Batesian mimics are predicted to lose their fitness advantage not only in the absence of an unpalatable model, but also when the mimic becomes relatively abundant. The phenotypic hybrid zone between mimetic and nonmimetic admiral butterflies, comprising the polytypic Limenitis arthemis species complex, offers an ideal opportunity to test these predictions because the position of the hybrid zone is hypothesized to be controlled by the geographic range of Battus philenor, the chemically defended model. We used 29 years of observational field data from a continental-scale butterfly monitoring program, the 4th of July Butterfly Counts, to show that (1) the advantage of mimicry does not extend beyond the range of the model, (2) in contrast to expectations, the mimicry complex is maintained even where the model is rare and (3) the sharp phenotypic transition between mimetic and nonmimetic admiral populations occurs over a very narrow spatial scale corresponding to the limit of the models range. These results suggest that, even at very low densities, there is selection for Batesian mimicry and it maintains the geographic position of this hybrid zone. Our findings highlight the value of large-scale, long-term citizen science monitoring programs for answering basic ecological and evolutionary questions.

Multitaxonomic Diversity Patterns along a Desert Riparian–Upland Gradient

Riparian areas are noted for their high biodiversity, but this has rarely been tested across a wide range of taxonomic groups. We set out to describe species richness, species abundance, and community similarity patterns for 11 taxonomic groups (forbs & grasses, shrubs, trees, solpugids, spiders, scarab beetles, butterflies, lizards, birds, rodents, and mammalian carnivores) individually and for all groups combined along a riparian–upland gradient in semiarid southeastern Arizona, USA. Additionally, we assessed whether biological characteristics could explain variation in diversity along the gradient using five traits (trophic level, body size, life span, thermoregulatory mechanism, and taxonomic affiliation). At the level of individual groups diversity patterns varied along the gradient, with some having greater richness and/or abundance in riparian zones whereas others were more diverse and/or abundant in upland zones. Across all taxa combined, riparian zones contained significantly more species than the uplands. Community similarity between riparian and upland zones was low, and beta diversity was significantly greater than expected for most taxonomic groups, though biological traits explained little variance in diversity along the gradient. These results indicate heterogeneity amongst taxa in how they respond to the factors that structure ecological communities in riparian landscapes. Nevertheless, across taxonomic groups the overall pattern is one of greater species richness and abundance in riparian zones, coupled with a distinct suite of species.

Do growing degree days predict phenology across butterfly species

Global climate change is causing shifts in phenology across multiple species. We use a geographically and temporally extensive data set of butterfly abundance across the state of Ohio to ask whether phenological change can be predicted from climatological data. Our focus is on growing degree days (GDD), a commonly used measure of thermal accumulation, as the mechanistic link between climate change and species phenology. We used simple calculations of median absolute error associated with GDD and an alternative predictor of phenology, ordinal date, for both first emergence and peak abundance of 13 butterfly species. We show that GDD acts as a better predictor than date for first emergence in nearly all species, and for peak abundance in more than half of all species, especially univoltine species. Species with less ecological flexibility, in particular those with greater dietary specialization, had greater predictability with GDD. The new method we develop for predicting phenology using GDD offers a simple...

The Disconnect Between Summer and Winter Monarch Trends for the Eastern Migratory Population: Possible Links to Differing Drivers

ABSTRACT The decline of the eastern population of the migratory monarch has become a topic of great concern, but has been based entirely on patterns observed in overwinter colony sizes. Less attention has been paid to population trends during other phases of the migratory cycle. Here, we present an analysis of trends using three monitoring programs, one focused on overwinter colony size and two focused on summer breeding grounds. We discovered an alarming steepening in the decline of winter colony size since 2008. However, population indices from two independent summer monitoring programs were characterized by high year-to-year variability and no statistically detectable trends over time. Despite the mismatch in summer and winter patterns, there is still an association between the yearly fluctuations between these key periods, suggesting a link in population dynamics throughout the year. Further, a suggestion of a downturn near the end of the summer time-series should be carefully tracked into the future. We discuss two possible reasons for this disconnect: 1) higher levels of variance or possibly biased sampling could weaken any statistical signal, and 2) losses during fall migration could potentially contribute to overwinter declines.

Butterfly Monitoring for Conservation

Monitoring butterfly populations is an essential component of their conservation. Some survey techniques measure occupancy, and simply determine the presence or absence of species, whereas other techniques measure butterfly abundance. Mark release recapture techniques involve marking the wings of a subset of a population, releasing and then recapturing them, and determining the proportion of marked individuals in the re-sampling. Distance sampling takes advantage of the decrease in probability of detection of individual butterflies as a function of increased distance from the observer. These techniques can both be used to estimate actual population size. Mark release recapture is the most rigorous, but also the most labor-intensive technique. It also carries risk of damage to individuals during the marking process. Distance sampling is statistically robust and doesn’t risk damaging butterflies by marking them. In some cases, the requirement for survey transects to be placed randomly within the population, and the assumption that the butterflies are distributed uniformly limit the application of the technique. For Pollard walks, surveyors walk a set route at a uniform pace. They count all butterflies within a prescribed distance (generally about 20 m). In addition to these systematic survey techniques, a variety of less formal monitoring protocols are also used. These include count circles, field trips, and wandering surveys. There are also a wide variety of online opportunities for interested individuals to submit butterfly observations. Researchers should consider the assumptions, advantages and disadvantages when selecting a technique.