Biology subjects

Waller, D. M.

Publications and source records attributed to Waller, D. M..

5 recordsLinked to original sources

bioRxiv2024

Twig Age 2.0: Adjusting twig age data for differences in palatability among taxa to track ungulate browsing over sites and time

O_LIUngulate browsing threatens forest tree regeneration and diversity across forests in North America and other temperate regions but is inadequately monitored. This reflects both inadequate commitment and the lack of efficient, reliable methods to accurately track these impacts across sites and over time. C_LIO_LIThe twig age method estimates time: how long twigs grow before being browsed, providing a direct measure of herbivory. The original method aged twigs on maple (Acer) seedlings, but it works well in other deciduous species. Given ungulate preferences for some species, it is important to adjust twig ages to correct for these. C_LIO_LIUsing multiple datasets from many species and sites across the upper Midwest, I confirm the power and sensitivity of the twig age method for assessing and comparing white-tailed deer impacts over time, among species, and across sites. Twig ages respond differently to seedling heights when deer are present, providing an additional indicator. I extend the original method to rank and adjust for differential browsing among species in two ways: using least square means from statistical models and using ratios to adjust values to an Acer saccharum standard. These adjustments match, supporting the use of either to accurately track shifts in browse pressure over time and across sites even when these differ in species composition. C_LIO_LIThe adjusted twig-age method is highly efficient, allowing a sole worker to score 100+ seedlings/saplings within an hour to accurately gauge real-time ungulate impacts at a site. The reliability, power, and versatility of adjusted twig age data set a standard for assessing browse pressure and provide an efficient vehicle to expand programs to monitor deer impacts across landscapes. C_LI

ecology↗

bioRxiv2023

Functional traits fail to predict long-term responses to climate change

AimEnvironmental conditions strongly affect the distribution and abundance of species via complex forces. Shifts in environmental conditions and differences in the speed and scale of these effects complicate our efforts to infer how species will respond to future environmental change. We test how 18 functional traits affect plant species responses to gradients in environmental conditions and 50-year shifts in climate. LocationWe analyzed 50-year shifts in the distribution and abundance of 153 plant species distributed across 284 sites in Wisconsin, USA. Time period1950s to 2000s. Major taxa studiedVascular plants (much of the flora of NE North America). MethodsWe used random forest and integrated hierarchical mixed models to test how plant abundances (and 50-year changes in abundance) track gradients in overstory, soil, and climatic conditions. ResultsWithin study periods, plant abundances reflect gradients in environmental conditions. Leaf traits affected local abundance (both directly and via trait-environment interactions) in the 1950s and 2000s. Strong soil and temperature effects in the 1950s have weakened while precipitation effects have strengthened. Although we expected these models to also predict how plants would respond to shifts in climate, they did not. Main conclusionsLags in species responses, increases in the stochastic forces affecting community assembly, and other forces limit the ability of models fitted to static data (e.g., space-for-time substitutions) to predict how plant species will respond to long-term shifts in environmental conditions. We must therefore be cautious about applying trait-based species distribution models to predict how climate change will affect species distributions and community structure.

ecology↗

bioRxiv2021

The role of pseudo-overdominance in maintaining inbreeding depression

Classical models that ignore linkage predict that deleterious recessive mutations should purge or fix within inbred populations, yet inbred populations often retain moderate to high segregating load. True overdominance could generate balancing selection strong enough to sustain inbreeding depression even within inbred populations, but this is considered rare. However, arrays of deleterious recessives linked in repulsion could generate appreciable pseudo-overdominance that would also sustain segregating load. We used simulations to explore how long pseudo-overdominant (POD) zones persist once created (e.g., by hybridization between populations fixed for alternative mildly deleterious mutations). Balanced haplotype loads, tight linkage, and moderate to strong cumulative selective effects all serve to maintain POD zones. Tight linkage is key, suggesting that such regions are most likely to arise and persist in low recombination regions (like inversions). Selection and drift unbalance the load, eventually eliminating POD zones, but this process is quite slow under strong pseudo-overdominance. Background selection accelerates the loss of weak POD zones but reinforces strong ones in inbred populations by disfavoring homozygotes. Models and empirical studies of POD dynamics within populations help us understand how POD zones may allow the load to persist, greatly affecting load dynamics and mating systems evolution.

evolutionary biology↗

bioRxiv2020

Accounting for underlying complexities identifies simple hierarchy of trait-environment relationships in Wisconsin forest understory communities

Plant species shift in abundance as environmental conditions change because traits adapt species to particular conditions. As a result, trait values shift along environmental gradients--the so-called trait-environment relationships. These relationships are often assessed by regressing community-weighted mean (CWM) traits on environmental gradients. Such regressions (CWMr) assume that local communities exhibit centered optimum trait-abundance relationships and that traits are not independent from one another. However, the shape of trait-abundance relationships can vary widely along environmental gradients--reflecting the interaction between traits and gradients--and traits are usually interrelated. Accounting for these complexities should improve our ability to accurately describe trait-environment relationships. We tested these ideas by analyzing how abundances of 185 herbaceous understory species distributed among 189 forested sites in Wisconsin, USA, varied in response to four functional traits (vegetative height-VH, leaf size-LS, leaf mass per area-LMA, and leaf carbon content) and six soil and climate variables. A generalized linear mixed model (GLMM) allowed us to assess how the shape of trait-abundance relationships changed along environmental gradients for the 24 trait-environment combinations simultaneously. We then compared the resulting trait-environment relationships to those estimated via CWMr. The GLMM identified five significant trait-environment relationships that together explained [~]40% of variation in species abundances across sites. Temperature played important roles with warmer and more seasonal sites favoring taller plants. Soil texture and temperature seasonality affected LS and LMA more modestly; these seasonality effects declined at more seasonal sites. Only some traits under certain conditions showed centered optimum trait- abundance relationships. Concomitantly, CWMr identified 17 significant trait-environment relationships including effects of temperature, precipitation, and soil on LMA as often reported in other studies. Despite this overidentification, CWMr failed to detect significant temperature-seasonality effects found in the GLMM. Modeling the complexity of how traits and environments interact to affect plant abundance allows us to identify and rank key trait- environment relationships. Although the GLMM model was more complex compared to single CWM regressions, it identified a simpler hierarchy of trait-environment relationships that accurately and reliably predicted responses of forest understory species to gradients in environmental conditions.

ecology↗

bioRxiv2020

Asymmetrical pegs in square holes? Functional and phylogenetic determinants of plant community assembly in temperate forest understories

Despite advances in community assembly theory, uncertainties remain regarding how ecological and evolutionary processes shape species distributions and communities. We analyzed patterns of occurrence for 139 herbaceous plant species across 257 forest stands in Wisconsin (USA) to test predictions from community assembly theory. Specifically, we applied Bayesian phylogenetic linear mixed effects models (PGLMMs) to examine how functional traits and phylogenetic relationships influence plant distributions along environmental gradients and how functional similarity and phylogenetic relatedness affect local species co-occurrence. Leaf height, specific leaf area, and seed mass mediate species distributions along edaphic, climatic, and light gradients. In contrast, functional trait similarity and phylogenetic relationships only weakly affect patterns of local co-occurrence. These results confirm that broad-scale plant distributions are largely shaped by ecological sorting along environmental gradients but suggest deterministic assembly rules based on niche differentiation and complementary resource use may not govern local species co-occurrence in homogeneous environments. Statement of authorshipJB conceived the idea for the study. DL, SJ, and DR collected the vegetation and functional trait data. JB analyzed the data with assistance from DL. KC, KS, TG, and DW secured funding for research and oversaw data collection. JB wrote the first draft of the manuscript, all authors contributed to manuscript revisions. Data accessibility statementUpon acceptance, data will be archived at Figshare (https://figshare.com/) and scripts used to analyze the data will be shared on Github (https://github.com/jaredjbeck/).

ecology↗