Charles F. Williams

Premise: Root hemiparasites form haustoria in belowground roots of hosts to extract nutrients and water from the surrounding hosts. Through parasitic symbiosis, these plants disproportionately affect plant communities relative to their abundance by reducing host size, altering nutrient flow, and eventually increasing local biodiversity. Their prevalence and potential as keystone species position hemiparasites as important drivers of community structure. Methods: In a 2‐year study at the Rocky Mountain Biological Laboratory, we selected paired presence and absence plots for three species of hemiparasitic Castilleja across seven study sites to explore the association of Castilleja with differences in the structure of montane plant communities. Our objectives were to (1) observe the relationship between three hemiparasitic Castilleja species and plant community diversity and composition and (2) assess the host range and preference for each species in situ using direct and indirect sampling. Percentage cover of all species was recorded to assess the effect of Castilleja presence on plant community diversity and composition. To assess host range and preference and to support nearest‐neighbor and indicator‐species analyses, we excavated Castilleja individuals to observe haustorial connections. Results: Across sites, species, and years, the presence of Castilleja was consistently correlated with increased plant biodiversity and site‐specific differences in community composition. Excavations suggested that Castilleja species are generalist hemiparasites with some preference for common, dominant hosts. Conclusions: Our results identify a positive relationship between Castilleja presence and local plant community diversity and support the interpretation that these species act as generalist hemiparasites.

Phylogenetic diversity is an important axis of biodiversity associated with ecosystem stability and productivity. However, climate change will threaten phylogenetic diversity when extinctions are phylogenetically clustered. Despite the importance of phylogenetic diversity for current and future ecosystems, and the potential unique insights it offers into communities, few studies have quantified its long-term changes. Here, we leverage a dataset spanning approximately 65 years and 1500 m of elevation in the Colorado Rocky Mountains to test for changes in phylogenetic diversity in angiosperm communities. We included four community types (sagebrush, spruce-fir, upland-herb, alpine), which vary in the direction and magnitude of changes in species richness over this period. We tested whether individual species’ responses to climate change could be predicted by phylogeny, including changes to abundance, constancy (% of sites occupied), and elevational range. We did not find phylogenetic signal in abundance change in any community, but we did find phylogenetic signal in both constancy shifts in alpine and elevational shifts in sagebrush communities. We then tested for changes in phylogenetic diversity across time for each community type. We found that phylogenetic diversity changed in the same direction as species richness in the sagebrush community, where both declined, and in the upland-herb, where both increased, with important roles for both species gains and losses in community phylogenetic composition. The alpine community did not change in phylogenetic diversity, although richness declined, while the spruce-fir community increased in phylogenetic diversity but did not change in richness, emphasizing the potential for changes in different aspects of diversity to be decoupled. Our work highlights that the impacts of climate change vary across communities, and that phylogeny is shaping changes in certain systems. Given the importance of phylogenetic diversity to ecosystem function, long term studies are essential for understanding how climate change impacts phylogenetic diversity in distinct community types with unique responses to climate change.

In recent years, the availability of airborne imaging spectroscopy (hyperspectral) data has expanded dramatically. The high spatial and spectral resolution of these data uniquely enable spatially explicit ecological studies including species mapping, assessment of drought mortality and foliar trait distributions. However, we have barely begun to unlock the potential of these data to use direct mapping of vegetation characteristics to infer subsurface properties of the critical zone. To assess their utility for Earth systems research, imaging spectroscopy data acquisitions require integration with large, coincident ground‐based datasets collected by experts in ecology and environmental and Earth science. Without coordinated, well‐planned field campaigns, potential knowledge leveraged from advanced airborne data collections could be lost. Despite the growing importance of this field, documented methods to couple such a wide variety of disciplines remain sparse. We coordinated the first National Ecological Observatory Network Airborne Observation Platform (AOP) survey performed outside of their core sites, which took place in the Upper East River watershed, Colorado. Extensive planning for sample tracking and organization allowed field and flight teams to update the ground‐based sampling strategy daily. This enabled collection of an extensive set of physical samples to support a wide range of ecological, microbiological, biogeochemical and hydrological studies. We present a framework for integrating airborne and field campaigns to obtain high‐quality data for foliar trait prediction and document an archive of coincident physical samples collected to support a systems approach to ecological research in the critical zone. This detailed methodological account provides an example of how a multi‐disciplinary and multi‐institutional team can coordinate to maximize knowledge gained from an airborne survey, an approach that could be extended to other studies. The coordination of imaging spectroscopy surveys with appropriately timed and extensive field surveys, along with high‐quality processing of these data, presents a unique opportunity to reveal new insights into the structure and dynamics of the critical zone. To our knowledge, this level of co‐aligned sampling has never been undertaken in tandem with AOP surveys and subsequent studies utilizing this archive will shed considerable light on the breadth of applications for which imaging spectroscopy data can be leveraged.

Floral colour is a fundamental signal that shapes plant–pollinator interactions. Despite theoretical reasons why floral colours might shift in representation along biotic and abiotic gradients, few studies have examined community‐level shifts in colour, and even fewer significant patterns have been detected. We examined floral colour on six replicated transects spanning 1,300 m in the Rocky Mountains of Colorado,USA. Along these transects, there is a hypothesized shift from bee‐dominated to fly‐dominated pollination with increasing elevation. The reflectance of flowers of 110 forb and shrub species was measured using a spectrophotometer, and was used to estimate three components of colour (hue, saturation and brightness) in relevant pollinator visual spaces. Percent cover data were collected from 67 sites and used to obtain community‐weighted mean (cwm) estimates of floral colour. We found strong patterns of elevational change in floral colour. Reflectance_cwmof shorter wavelengths (UVBthrough human blue, 300–500 nm) generally decreased linearly with elevation, while reflectance_cwmof longer wavelengths (human green through red, 500–700 nm) showed hump‐shaped patterns with highest reflectance at intermediate elevations. With respect to pollinators, saturation_cwmincreased significantly with elevation in both bee and fly visual spaces, while brightness contrast_cwmshowed a hump‐shaped pattern in bee space and a decline with elevation in fly visual space. For hue, cover of species perceived as bee‐blue declined with elevation, while cover of bee‐UV‐green species showed a hump‐shaped pattern. In comparison, we detected no elevational shifts in floral hues as perceived by flies. Synthesis. Hue patterns are consistent with the hypothesis that bee pollinators have shaped the geography of floral colour. The roles of fly pollinators and of abiotic drivers are more difficult to infer, although the drop in floral brightness at high elevations is consistent with predictions that low temperatures and more intense ultraviolet radiation should favour increased pigment concentrations there. Our results indicate that floral colour can be dynamic yet predictable across the landscape, a pattern that provides opportunities to tease apart the ecological and evolutionary drivers of this important plant trait.

Documenting and predicting patterns of vegetation change over time are challenging due to a lack of sufficiently detailed historical data for comparison. Montane plant communities are expected to respond to anthropogenic disturbance, including climate change, in complex ways dependent on component species' responses to changing abiotic and biotic conditions. To investigate the patterns and possible causes of temporal changes in montane plant communities, we resampled 121 transects surveyed by Jean Langenheim from 1948 to 1952 in the East River Basin near Crested Butte, Colorado, U.S.A. Langenheim quantified the composition of the four predominant community types (sagebrush, spruce-fir, upland-herbaceous, and alpine) at sites ranging from 2600 to 4100 m in elevation. Our resurvey of the same sites 65 years later revealed that all four communities currently have much higher levels of heterogeneity among sites and have experienced significant changes in species composition and dominance. Composition...

Quantitative trait locus (QTL) mapping is a first step toward understanding the genetic basis of adaptive evolution and may also reveal reproductive incompatibilities unique to hybrids. In plants, the shift from outcrossing to self-pollination is common, providing the opportunity for comparisons of QTL architecture among parallel evolutionary transitions. We used QTL mapping in hybrids between the bee-pollinated monkeyflower Mimulus lewisii and the closely related selfer Mimulusparishii to determine the genetic basis of divergence in floral traits and flowering time associated with mating-system evolution, and to characterize hybrid anther sterility. We found a moderately polygenic and highly directional basis for floral size evolution, suggesting adaptation from standing variation or in pursuit of a moving optimum, whereas only a few major loci accounted for substantial flowering-time divergence. Cytonuclear incompatibilities caused hybrid anther sterility, confounding estimation of reproductive organ QTLs. The genetic architecture of floral traits associated with selfing in M.parishii was primarily polygenic, as in other QTL studies of this transition, but in contrast to the previously characterized oligogenic basis of a pollinator shift in close relatives. Hybrid anther sterility appeared parallel at the molecular level to previously characterized incompatibilities, but also raised new questions about cytonuclear co-evolution in plants.

Floral display size represents a tradeoff between the benefits of increased pollinator visitation and the quantity of pollen received vs. the costs of increased self‐pollination and reduced pollination quality. Plants with large floral displays often are more attractive to pollinators, but pollinators visit more flowers per plant. Intraplant foraging movements should increase self‐pollination through geitonogamy, lowering outcrossing rates in large plants. Local genetic structure should also increase inbreeding and decrease outcrossing estimates, if pollinators move between neighboring, related plants. These predictions were tested in a population of larkspurs (Delphinium barbeyi) in Colorado. Allozymes were used to estimate outcrossing rates of plants varying in display size. Floral displays varied widely (2–1400 flowers; 1–26 inflorescences per plant), and outcrossing rate decreased significantly with increasing display size. Large, multistalked plants self over twice as frequently as single‐stalked plants (46 vs. 21%). Local population structure is significant, and biparental inbreeding depresses outcrossing in plants surrounded by genetically similar neighbors. Protandry, coupled with stereotypical bottom‐up pollinator foraging, reduces self‐fertilization by autogamy or geitonogamy within inflorescences. Selfing is predominantly (>60%) by geitonogamy between inflorescences in large plants. Geitonogamy may be a significant cost to plants with large floral displays if inbreeding depression and/or pollen and ovule discounting results. If so, floral display size, particularly inflorescence number, may be under contrasting selection for pollination quantity vs. quality.

Clone size of plants of Andropogon gerardii from Konza Prairie Biological Station, Manhattan, Kansas was estimated from spatial patterns of genetic variation, using proteins detected by starch gel electrophoresis and DNA content (ploidy) measured by flow cytometry. Unique multi-locus protein banding patterns and differences in ploidy were used to exclude plants as members of the same clone. Individual clones averaged about 2 m in diameter and areas of prairie of 100 m2 were calculated to contain an average of 31.8 genetic individuals.

Contemplate the descent of a piece of DNA (or RNA in organisms using this as their genetic material). The DNA is copied, and copies are passed to descendants. If the copies were error-free we could rightly think of them as perfect clones that pass down indefinitely through the eons. This logic led Richard Dawkins to speak of immortal coils in his book on selfish genes; here, it instead brings up issues of the common ancestry of genes and of individuals, and of the definition and consequences of inbreeding and outbreeding, the subjects of this chapter. When two individuals share one or more ancestor, they are relatives, both in common parlance and by technical definition in biology. The consequence of their mating is inbreeding, that is, the production of offspring receiving copies of a given gene through both mother and father that can be traced to the common ancestor(s). These gene copies are identical by descent (IBD; not to be confused with an acronym for inbreeding depression, see below), a shorthand for “identical by the fact of descending as copies of the same original piece of DNA”. The probability that two gene copies are IBD in a diploid individual, or its inbreeding coefficient, symbolized by f, is a simple function of the genetic relatedness of its parents and the segregation of genes during meiosis and gametogenesis. Because the probability is one-half that two gametes from the same individual carry identical gene copies, fertilization by self produces f of one-half, a brother-sister mating or parent-offspring mating produces f of one-quarter, a first-cousin mating produces f of one-sixteenth, and so on (see “Measurement of Inbreeding and Outbreeding,” below). In these examples, we assume that neither common ancestor(s) nor parents themselves are inbred; such inbreeding reflects additional common ancestry and so inflates f. From all of this, a definition of outbreeding as “mating of nonrelatives” follows automatically. As just defined, inbreeding and outbreeding rely on an absolute measure of relatedness. An alternative definition that may be of more value in real, finite populations (as opposed to ideal, infinite ones) is that inbreeding is mating with relatives more often than expected by chance, and outbreeding the opposite.