Historical and Geographic Context for the Evolution of Climate Niche Breadth in Temperate Plants

In order to predict how species will respond to global climate change, scientists must understand the relationships between traits, fitness, environments and distributions. Niche theory provides a useful framework. Niche breadth describes the range of environmental conditions necessary for population growth. Among these conditions, climate is especially important. Climate niche breadth in turn may reflect a confluence of different forces. This dissertation presents a series of projects that assess the relative roles of historical, geographic and population processes that contribute to climate niche breadth in temperate plants. The first project evaluates the predictive power of a classical hypothesis. If gene flow slows divergent adaptation, then range fragmentation should promote niche breadth. By quantifying the relationships between environmental difference, geographic distance and genetic isolation among European plants, I show that the effect of allopatry on niche breadth depends on the role of the geographic distance among populations. The remaining projects focus in increasingly finer detail on the evolution of niche breadth in a taxonomically complex group. Dodecatheon sect. Dodecatheon grow in diverse habitats across North America. They have confounded taxonomists with polyploidy, hybridization and convergent adaptation. Currently recognized species are either widespread or rare microclimate specialists. First, with multilocus phylogenetics, I show that the difference in niche breadth among rare and widespread species is not simply due to differences in environmental tolerance. In eastern North America, geographic heterogeneity and paleoclimate history strongly contribute to taxonomic rarity. The next project focuses on this group. Both rare eastern species are considered glacial relicts. I test this hypothesis by combining ecophysiological and population genetic data in a new phylogeographic framework. The analysis shows that the match between traits and habitats is largely due to local gene flow and selection rather than migration and habitat sorting. Finally, through morphometrics, cytology, population genetics and greenhouse experiments, I show that dynamic polyploidy permits local movement of alleles between rare and widespread taxa. Overall, these results suggest that anthropogenic climate change may threaten biodiversity not by forcing impossible migrations, but by promoting hybridization and complicating taxonomy just as it has in the past

Ontogenetic trait variation influences tree community assembly across environmental gradients

Intraspecific trait variation is hypothesized to influence the relative importance of community assembly mechanisms. However, few studies have explicitly considered how intraspecific trait variation among ontogenetic stages influences community assembly across environmental gradients. Because the relative importance of abiotic and biotic assembly mechanisms can differ among ontogenetic stages within and across environments, ontogenetic trait variation may have an important influence on patterns of functional diversity and inferred assembly mechanisms. We tested the hypothesis that variation in functional diversity across a topo-edaphic gradient differs among ontogenetic stages and that these patterns reflect a shift in the relative importance of different assembly mechanisms. In a temperate forest in the Missouri Ozarks, USA, we compared functional diversity of leaf size and specific leaf area (SLA) of 34 woody plant species at two ontogenetic stages (adults and saplings) to test predictions about how the relative importance of abiotic and biotic filtering changes among adult and sapling communities. Local communities of adults had lower mean SLA and lower functional dispersion of SLA than expected by chance, particularly at the resource-limited end of the topo-edaphic gradient, suggesting an important role for abiotic filtering among co-occurring adults. In contrast, local communities of saplings often had higher functional dispersion of leaf size and SLA than expected by chance regardless of their location along the topo-edaphic gradient, suggesting an important role for biotic filtering among co-occurring saplings. Moreover, the overall strength of trait-environment relationships varied between saplings and adults for both leaf traits, generally resulting in stronger environmental shifts in mean trait values and trait dispersion for adults relative to saplings. Our results illustrate how community assembly mechanisms may shift in their relative importance during ontogeny, leading to variable patterns of functional diversity across environmental gradients. Moreover, our results highlight the importance of integrating ontogeny, an important axis of intraspecific trait variability, into approaches that use plant functional traits to understand community assembly and species coexistence

Accurate forest projections require long-term wood decay experiments because plant trait effects change through time.

Whether global change will drive changing forests from net carbon (C) sinks to sources relates to how quickly deadwood decomposes. Because complete wood mineralization takes years, most experiments focus on how traits, environments and decomposer communities interact as wood decay begins. Few experiments last long enough to test whether drivers change with decay rates through time, with unknown consequences for scaling short-term results up to long-term forest ecosystem projections. Using a 7 year experiment that captured complete mineralization among 21 temperate tree species, we demonstrate that trait effects fade with advancing decay. However, wood density and vessel diameter, which may influence permeability, control how decay rates change through time. Denser wood loses mass more slowly at first but more quickly with advancing decay, which resolves ambiguity about the after-life consequences of this key plant functional trait by demonstrating that its effect on decay depends on experiment duration and sampling frequency. Only long-term data and a time-varying model yielded accurate predictions of both mass loss in a concurrent experiment and naturally recruited deadwood structure in a 32-year-old forest plot. Given the importance of forests in the carbon cycle, and the pivotal role for wood decay, accurate ecosystem projections are critical and they require experiments that go beyond enumerating potential mechanisms by identifying the temporal scale for their effects

Ecological correlates of risk and incidence of West Nile virus in the United States

West Nile virus, which was recently introduced to North America, is a mosquito-borne pathogen that infects a wide range of vertebrate hosts, including humans. Several species of birds appear to be the primary reservoir hosts, whereas other bird species, as well as other vertebrate species, can be infected but are less competent reservoirs. One hypothesis regarding the transmission dynamics of West Nile virus suggests that high bird diversity reduces West Nile virus transmission because mosquito blood-meals are distributed across a wide range of bird species, many of which have low reservoir competence. One mechanism by which this hypothesis can operate is that high-diversity bird communities might have lower community-competence, defined as the sum of the product of each species’ abundance and its reservoir competence index value. Additional hypotheses posit that West Nile virus transmission will be reduced when either: (1) abundance of mosquito vectors is low; or (2) human population density is low. We assessed these hypotheses at two spatial scales: a regional scale near Saint Louis, MO, and a national scale (continental USA). We found that prevalence of West Nile virus infection in mosquito vectors and in humans increased with decreasing bird diversity and with increasing reservoir competence of the bird community. Our results suggest that conservation of avian diversity might help ameliorate the current West Nile virus epidemic in the USA

Data and Code for "Accurate forest ecosystem projections from wood decay experiments depend on temporal scale"

(Publications) This data is associated with the forthcoming publication in PNaS, titled "Accurate forest ecosystem projections from wood decay experiments depend on temporal scale."(Publication Status) Published in PNaS: https://www-pnas-org.ezproxy.lib.usf.edu/content/early/2020/05/12/190916611

Heterogeneity of Lycopodium clavatum patches and the distribution and herbivory strategy of Notodontid moth larvae and their Ichneumonid parasites

In this study, a novel system in which a notodontid moth larva (Family Notodontidae) uses Lycopodium clavatum (Family Lycopodiaceae), a cosmopotlitainly distributed clubmoss, as a hostplant. The larva and itself is host to no fewer than three parasitoid wasp species, including two ectoparasites, one of which is from the Ichneumonid genus Netelia. Distribution of larvae and damage to reproductive structures by larvae within the L. clavatum population are explained in terms of potential resource preference by the larvae. Larvae do not exhibit any measurable preference for reproductive structures with a given number of stobili, a character known to be associated with different cytotypes of this highly variable plant species. The findings indicate that distribution of larvae and their patterns of herbivory must be explained either using other characters of the host plant, or are due to other factors such as oviposition behavior of parent moths and parasitoids. En este papel se describe un sistema nuevo donde la larva de una polilla de la familia Notodontidae no identificada utiliza Lycopodium clavatum, (Familia Lycopodiaceae), un licopodio que se encuentra por todo el mundo, como planta-anfitrion. La larva propia es anfitrión para tres especies de avispas parasíticas, incluyendo una del género Netelia (Familia Ichneumonidae). La distribución de las larvas y su daño a las estructuras reproductoras de L. clavatum se explica cómo preferencia de las larvas para recursos. Las larvas no prefieren las estructuras reproductoras con numéros de estróbilos diferentes, un carácter que se relaciona con variedades diferentes de esta planta variablisima. Los datos presentados indican que la distribución de las larvas y su herbívoro necesitan otra explicación, como otros caracteres de la planta o el comportamiento de las polillas adultas y los parásitos.https://digitalcommons.usf.edu/tropical_ecology/1485/thumbnail.jp

Heterogeneity of Lycopodium clavatum patches and the distribution and herbivory strategy of Notodontid moth larvae and their Ichneumonid parasites

In this study, a novel system in which a notodontid moth larva (Family Notodontidae) uses Lycopodium clavatum (Family Lycopodiaceae), a cosmopotlitainly distributed clubmoss, as a hostplant. The larva and itself is host to no fewer than three parasitoid wasp species, including two ectoparasites, one of which is from the Ichneumonid genus Netelia. Distribution of larvae and damage to reproductive structures by larvae within the L. clavatum population are explained in terms of potential resource preference by the larvae. Larvae do not exhibit any measurable preference for reproductive structures with a given number of stobili, a character known to be associated with different cytotypes of this highly variable plant species. The findings indicate that distribution of larvae and their patterns of herbivory must be explained either using other characters of the host plant, or are due to other factors such as oviposition behavior of parent moths and parasitoids. En este papel se describe un sistema nuevo donde la larva de una polilla de la familia Notodontidae no identificada utiliza Lycopodium clavatum, (Familia Lycopodiaceae), un licopodio que se encuentra por todo el mundo, como planta-anfitrion. La larva propia es anfitrión para tres especies de avispas parasíticas, incluyendo una del género Netelia (Familia Ichneumonidae). La distribución de las larvas y su daño a las estructuras reproductoras de L. clavatum se explica cómo preferencia de las larvas para recursos. Las larvas no prefieren las estructuras reproductoras con numéros de estróbilos diferentes, un carácter que se relaciona con variedades diferentes de esta planta variablisima. Los datos presentados indican que la distribución de las larvas y su herbívoro necesitan otra explicación, como otros caracteres de la planta o el comportamiento de las polillas adultas y los parásitos.https://digitalcommons.usf.edu/tropical_ecology/1485/thumbnail.jp

When a tree falls: Controls on wood decay predict standing dead tree fall and new risks in changing forests.

When standing dead trees (snags) fall, they have major impacts on forest ecosystems. Snag fall can redistribute wildlife habitat and impact public safety, while governing important carbon (C) cycle consequences of tree mortality because ground contact accelerates C emissions during deadwood decay. Managing the consequences of altered snag dynamics in changing forests requires predicting when snags fall as wood decay erodes mechanical resistance to breaking forces. Previous studies have pointed to common predictors, such as stem size, degree of decay and species identity, but few have assessed the relative strength of underlying mechanisms driving snag fall across biomes. Here, we analyze nearly 100,000 repeated snag observations from boreal to subtropical forests across the eastern United States to show that wood decay controls snag fall in ways that could generate previously unrecognized forest-climate feedback. Warmer locations where wood decays quickly had much faster rates of snag fall. The effect of temperature on snag fall was so strong that in a simple forest C model, anticipated warming by mid-century reduced snag C by 22%. Furthermore, species-level differences in wood decay resistance (durability) accurately predicted the timing of snag fall. Differences in half-life for standing dead trees were similar to expected differences in the service lifetimes of wooden structures built from their timber. Strong effects of temperature and wood durability imply future forests where dying trees fall and decay faster than at present, reducing terrestrial C storage and snag-dependent wildlife habitat. These results can improve the representation of forest C cycling and assist forest managers by helping predict when a dead tree may fall

Ontogenetic trait variation influences tree community assembly across environmental gradients

Intraspecific trait variation is hypothesized to influence the relative importance of community assembly mechanisms. However, few studies have explicitly considered how intraspecific trait variation among ontogenetic stages influences community assembly across environmental gradients. Because the relative importance of abiotic and biotic assembly mechanisms can differ among ontogenetic stages within and across environments, ontogenetic trait variation may have an important influence on patterns of functional diversity and inferred assembly mechanisms. We tested the hypothesis that variation in functional diversity across a topo-edaphic gradient differs among ontogenetic stages and that these patterns reflect a shift in the relative importance of different assembly mechanisms. In a temperate forest in the Missouri Ozarks, USA, we compared functional diversity of leaf size and specific leaf area (SLA) of 34 woody plant species at two ontogenetic stages (adults and saplings) to test predictions about how the relative importance of abiotic and biotic filtering changes among adult and sapling communities. Local communities of adults had lower mean SLA and lower functional dispersion of SLA than expected by chance, particularly at the resource-limited end of the topo-edaphic gradient, suggesting an important role for abiotic filtering among co-occurring adults. In contrast, local communities of saplings often had higher functional dispersion of leaf size and SLA than expected by chance regardless of their location along the topo-edaphic gradient, suggesting an important role for biotic filtering among co-occurring saplings. Moreover, the overall strength of trait-environment relationships varied between saplings and adults for both leaf traits, generally resulting in stronger environmental shifts in mean trait values and trait dispersion for adults relative to saplings. Our results illustrate how community assembly mechanisms may shift in their relative importance during ontogeny, leading to variable patterns of functional diversity across environmental gradients. Moreover, our results highlight the importance of integrating ontogeny, an important axis of intraspecific trait variability, into approaches that use plant functional traits to understand community assembly and species coexistence

ZanneTysonPlantTraits

These are leaf and wood plant traits data for 21 species from Tyson Research Center, MO, USA