Biology subjects

Crone, E. E.

Publications and source records attributed to Crone, E. E..

8 recordsLinked to original sources

bioRxiv2026

Spatiotemporal patterns of breeding challenge the successive broods model in a migratory butterfly

Migration is widely recognized as a strategy for animals to track seasonally shifting resources. Yet, seasonal and spatial dynamics of migration are challenging to study, particularly for difficult-to-track insects. Among insects, monarch butterflies (Danaus plexippus) have a well-documented fall migration, but spring breeding recolonization remains poorly understood, particularly for the western population. We conducted multi-year surveys across six regions in the western United States to characterize monarch breeding phenology and evaluate three related hypotheses: (i) the successive broods model, with discrete generations shifting activity across the breeding range, (ii) a diffusion-like expansion model with overlapping breeding periods, and (iii) a mid-summer lull model with temporary summer declines in breeding for areas near the overwintering habitat. Monarch immature presence served as an indicator of local breeding activity. Our results do not support the successive broods or mid-summer lull hypotheses. Breeding onset occurred earlier near overwintering areas and gradually expanded north-and eastward, with sustained activity in many regions throughout the season. Termination of breeding also occurred earlier at more distant sites, resulting in longer breeding activity nearer to overwintering habitat. Immature monarch density declined with distance from overwintering areas at onset and termination, suggesting delayed colonization of peripheral regions. Together, these results support a diffusion-like expansion of breeding rather than sequential generational replacement. Western monarchs also do not initiate or terminate breeding in close synchrony with host plant availability, contrary to predictions from resource-tracking theory. These findings highlight fundamental differences between western monarch breeding dynamics and paradigms for eastern monarchs, demonstrating that a single species can employ fundamentally different spatial strategies for recolonizing its breeding range in different regions. More generally, these results distinguish insect migration from systems with direct movements between wintering and breeding habitats, and underscore the value of long-term, landscape-scale monitoring for resolving habitat use across heterogeneous environments.

ecology↗

bioRxiv2023

Estimating butterfly population trends from sparse monitoring data using Generalized Additive Models

Concerns of declines in insects and population level responses to climate change have highlighted the importance of estimating trends in abundance and phenology from existing monitoring data. As the taxa with the most systematic monitoring data, butterflies are a frequent focus for understanding trends in insects. Even so, ecologists often have only sparse monitoring data for at-risk butterfly populations. As existing statistical techniques are typically poorly suited to such data, these at-risk populations are frequently excluded from analyses of butterfly trends. Here we present guidelines for estimating population trends from sparse butterfly monitoring data using generalized additive models (GAMs), based on extensive simulations and our experiences fitting hundreds of butterfly species. These recommendations include pre-processing steps, model structure choices, and post-hoc analysis decisions that reduce bias and prevent or mitigate biologically implausible model fits. We also present the ButterflyGamSim package for the programming language R, available at https://github.com/cbedwards/butterflyGamSims. This open source software provides tools for ecologists and applied statisticians to simulate realistic butterfly monitoring data and test the efficacy of different GAM model choices or monitoring schemes.

ecology↗

bioRxiv2020

Contrasting effects of land cover on nesting habitat use and reproductive output for bumble bees

O_LIUnderstanding habitat quality is central to understanding the distributions of species on the landscape, as well as to conserving and restoring at-risk species. Although it is well-known that many species require different resources throughout their life cycles, pollinator conservation efforts focus almost exclusively on forage resources. C_LIO_LIHere, we evaluate nesting habitat for bumble bees by locating nests directly on the landscape. We compared colony density and colony reproductive output for Bombus impatiens, the common eastern bumble bee, across three different land cover types (hay fields, meadows, and forests). We also recorded nest site characteristics, e.g., the position of each nest site, for all Bombus nests located during surveys to tease apart species-specific patterns of habitat use. C_LIO_LIWe found that B. impatiens nests exclusively underground in two natural land cover types, forests and meadows, but not in hay fields. B. impatiens nested at similar densities in both in meadows and forests, but colonies in forests had much higher reproductive output. C_LIO_LIIn contrast to B. impatiens, B. griseocollis frequently nested on the surface of the ground and was almost always found in meadows. B. bimaculatis nests were primarily below ground in meadows. B. perplexis nested below ground in all three habitat types, including hay fields. C_LIO_LIFor some bumble bee species in this system, e.g., B. griseocollis and B. bimaculatis, meadows, the habitat type with abundant forage resources, may be sufficient to maintain them throughout their life cycles. However, B. impatiens might benefit from heterogeneous landscapes with forests and meadows. Further research would be needed to evaluate whether hay fields are high-quality nesting sites for the one species that used them, B. perplexis. C_LIO_LISynthesis and applications. In the past, Bombus nesting studies have been perceived as prohibitively labor-intensive. This example shows that it is possible to directly measure nesting habitat use and quality for bumble bee species. Applying these methods to more areas, especially areas where at-risk Bombus spp. are abundant, is an important next step for identifying bumble bee habitat needs throughout their life cycles. C_LI

ecology↗

bioRxiv2020

Fitting phenological curves with GLMMs

Estimating population abundance is central to population ecology. With increasing concern over declining insect populations, estimating trends in abundance has become even more urgent. At the same time, there is an emerging in interest in quantifying phenological patterns, in part because phenological shifts are one of the most conspicuous signs of climate change. Existing techniques to fit activity curves (and thus both abundance and phenology) to repeated transect counts of insects (a common form of data for these taxa) frequently fail for sparse data, and often require advanced knowledge of statistical computing. These limitations prevent us from understanding both population trends and phenological shifts, especially in the at-risk species for which this understanding is most vital. Here we present a method to fit repeated transect count data with Gaussian curves using linear models, and show how robust abundance and phenological metrics can be obtained using standard regression tools. We then apply this method to eight years of Baltimore checkerspot data using generalized linear models (GLMs). This case study illustrates the ability of our method to fit even years with only a few non-zero survey counts, and identifies a significant negative relationship between population size and annual variation in thermal environment (in growing degree days). We believe our new method provides a key tool to unlock previously-unusable sparse data sets, and may provide a useful middle ground between ad hoc metrics of abundance and phenology and custom-coded mechanistic models.

ecology↗

bioRxiv2020

Bumblebee worker body size affects new worker production in different resource environments

O_LIBehavior and organization of social groups is thought to be vital to the functioning of societies, yet the contributions of various roles within social groups have been difficult to quantify. A common approach to quantifying these role-based contributions is evaluating the performance of individuals at conducting certain roles, these studies ignore how these performances might scale up to effects at the population-level. Manipulative experiments are another common approach to determine population-level effects, but they often ignore potential feedbacks associated with these various roles. C_LIO_LIHere, we evaluate the effects of worker size distribution in bumblebee colonies on worker production, using functional linear models. Functional linear models are a recent correlative technique that has been used to assess lag effects of environmental drivers on plant performance. We demonstrate potential applications of this technique to explore contributions of social animals to ecological phenomenon. C_LIO_LIWe found that the worker size distribution differentially affected new worker production across three resource environments. Specifically, more larger workers had mostly positive effects and more smaller workers had negative effects on worker production. Most of these effects were only detected under low or fluctuating resource environments suggesting that the advantage of colonies with larger-bodied workers becomes more apparent under stressful conditions. C_LIO_LIWe demonstrate the wider ecological application of functional linear models. We highlight the advantages and limitations when considering these models, and how they are a valuable complement to many of these performance-based and manipulative experiments. C_LI

ecology↗

bioRxiv2019

Accounting for imperfect detection in species with sessile life cycle stages: a case study of bumble bee colonies

O_LIFor bumble bees, colonies (not individual workers) are the functional unit of the population. Estimates of colony density are thus critical for understanding population distribution and trends of this important pollinator group. Yet, surveys of bumble bee colonies and other taxa with sessile life cycle states rarely account for imperfect detection.\nC_LIO_LIHere we demonstrate the use of mark-recapture methods to estimate the density of bumble bee colonies across the landscape using standardized survey protocols.\nC_LIO_LIWe found that the probability of detecting colonies in standardized surveys varied considerably across space, through time, and among colonies.\nC_LIO_LIUsing simulations, we also show that imperfect detection can obscure true variation in density among plots, or generate spurious variation in counts even when all plots have the same density. In both cases, we show that mark-recapture can be used to generate unbiased estimates of density, with relatively low search effort compared to conventional survey methods for bumble bee colonies.\nC_LIO_LIOur study illustrates the advantages of mark-recapture for optimizing survey protocols for species with cryptic and sessile life cycle stages, which will be a valuable tool in ongoing studies of pollinator nesting ecology.\nC_LI

ecology↗

bioRxiv2017

Predators or mutualists? Lack of dispersal distance benefits and small caching profits makes scatterhoarding rodents antagonists of oaks

Numerous interactions between plants and animals vary in their outcome between antagonism and mutualism, but it has proven to be difficult to quantify their final outcome. Interactions between plants and scatterhoarding animals provide a prime example of this phenomenon. Scatterhoarders consume large quantities of seeds (potentially reducing plant establishment), yet also disperse seeds and bury them in shallow caches (potentially improving recruitment). However, it has been rarely determined which role prevails for particular plant species. We demonstrate how plant-scatterhoarder interactions can be placed at the antagonism-mutualism continuum, with interactions between rodents and two oaks species (sessile oak Quercus petraea, and red oak Q. rubra) as an empirical example. Our approach consists of quantifying the net outcome of the interaction through assembling different vital rates (e.g. probability of seedling recruitment with and without rodents; near and far from conspecific trees; with and without seed pilferage) piecewise with a simple mathematical model. Our results indicate that during the period of the study, interactions between scatterhoarding rodents and both focal oaks were antagonistic. Even though acorn burial increased the likelihood of seedling establishment, this effect was not strong enough to compensate for the costs of seed predation. Furthermore, we found no evidence that the short-distance transportation that is usually provided by small mammals benefited early oak recruitment. Our study demonstrates how readily accessible field data can be used to gauge the outcomes in conditional mutualisms.

ecology↗

bioRxiv2017

Correlated seed failure as an environmental veto to synchronize reproduction of masting plants

Highly variable, synchronized seed production, called masting, is a widespread reproductive strategy in plants. Resource dynamics, pollination success, and, as described here, environmental veto, are possible proximate mechanisms of masting. We extended the resource budget model of masting with correlated and uncorrelated reproductive failure, and ran this model across its parameters space. Next, we parametrized the model based on a 16-year seed production data for red (Quercus rubra) and white (Q. alba) oaks. Simulations showed that resource dynamics and reproduction failure produce masting even in the absence of pollen coupling. In concordance, in both species, among-year variation in resource gain and correlated reproductive failure were necessary and sufficient to produce masting. Environmental variation is a form of reproduction failure caused by environmental veto that may drive large-scale synchronization without density-dependent pollen limitation. Reproductive-inhibiting weather events are prevalent in ecosystems, suggesting that these described mechanisms likely operate in many masting systems.

ecology↗