Herbivore damage is generally detrimental to plant fitness, and the evolutionary response of plant populations to damage can involve either increased resistance or increased tolerance. While characters that contribute to resistance, such as secondary chemicals and trichomes, are relatively well understood, characters that contribute to a plant's ability to tolerate damage have received much less attention. Using Helianthus annuus (wild sunflower) and simulated damage of Haplorhynchites aeneus (head-clipping weevil) as a model system, we examined morphological characters and developmental processes that contribute to compensatory ability. We performed a factorial experiment that included three levels of damage (none, the first two, or the first four inflorescences were clipped with scissors) and eight sires each mated to four dams. We found that plants compensated fully for simulated head-clipper damage and that there was no variation among plant families in compensatory ability: seed production and mean seed mass did not vary among treatments, and sire ϫ treatment interactions were not significant. Plants used four mechanisms to compensate for damage: (1) Clipped plants produced significantly more inflorescences than unclipped plants. Plants produced these additional inflorescences on higher order branches at the end of the flowering season. (2) Clipped plants filled significantly more seeds in their remaining heads than did unclipped plants.(3) Clipped plants, because they effectively flowered later than unclipped plants, were less susceptible to damage by seedfeeding herbivores other than Haplorhynchites. (4) In later heads, seed size was greater on clipped plants, which allowed mean seed size to be maintained in clipped plants. Although there was genetic variation among the families used in this experiment for most of the characters associated with compensation for damage (seed number, mean seed size, mean flowering date, length of the flowering period, and branching morphology), in analyses of these characters, no sire ϫ treatment interactions were significant indicating that all of the families relied on similar mechanisms to compensate for damage.

Abstract. Herbivore damage is generally detrimental to plant fitness, and the evolutionary response of plant populations to damage can involve either increased resistance or increased tolerance. While characters that contribute to resistance, such as secondary chemicals and trichomes, are relatively well understood, characters that contribute to a plant's ability to tolerate damage have received much less attention. Using Helianthus annuus (wild sunflower) and simulated damage of Haplorhynchites aeneus (head-clipping weevil) as a model system, we examined morphological characters and developmental processes that contribute to compensatory ability. We performed a factorial experiment that included three levels of damage (none, the first two, or the first four inflorescences were clipped with scissors) and eight sires each mated to four dams. We found that plants compensated fully for simulated head-clipper damage and that there was no variation among plant families in compensatory ability: seed production and mean seed mass did not vary among treatments, and sire ϫ treatment interactions were not significant. Plants used four mechanisms to compensate for damage: (1) Clipped plants produced significantly more inflorescences than unclipped plants. Plants produced these additional inflorescences on higher order branches at the end of the flowering season. (2) Clipped plants filled significantly more seeds in their remaining heads than did unclipped plants. (3) Clipped plants, because they effectively flowered later than unclipped plants, were less susceptible to damage by seedfeeding herbivores other than Haplorhynchites. (4) In later heads, seed size was greater on clipped plants, which allowed mean seed size to be maintained in clipped plants. Although there was genetic variation among the families used in this experiment for most of the characters associated with compensation for damage (seed number, mean seed size, mean flowering date, length of the flowering period, and branching morphology), in analyses of these characters, no sire ϫ treatment interactions were significant indicating that all of the families relied on similar mechanisms to compensate for damage.

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At Arapaho Prairie, in the sandhills of western Nebraska, the dioecious annual Croton texensis (Euphorbiaceae) exhibits biased sex ratios. Moreover, the direction of bias changes from year to year: in 1994 the study population was significantly female biased, in 1995 and 1996 it was significantly male biased, and in 1997 and 1998 the sex ratio did not differ from 1 : 1. Such variation in the observed sex ratio in plants is frequently attributed to environmental sex determination (ESD), which is favored by natural selection if the rate of fitness gain across an environmental gradient is greater for one sex than the other. We performed experiments to determine: (1) whether variation in the sex ratio is correlated with environmental conditions, as would be expected if ESD is operating, and (2) whether ESD, if present, would be favored by natural selection. In a common garden experiment in which water and fertilizer were manipulated the sex ratio was marginally male biased in treatments in which water was added, but not different from 1 : 1 in other treatments. In field plots into which seeds were planted none of several soil characteristics, nor overall plot quality for C. texensis (measured as average plant biomass) were correlated with plot sex ratio. However, plots in which a large number of planted seeds emerged tended to be female biased. These results provide very weak evidence for sex ratio bias across an environmental gradient, and thus provide little evidence for ESD. Moreover, sex-by-environment interactions for fitness, which are required for the evolution of ESD, were absent for all measured variables. Thus, ESD does not appear to be favored by natural selection in this population. Instead, these biases may have been caused by differences between the sexes in germination and/or early mortality.

Landscape disturbance models consistently explain variation in ecological integrity across large landscapes. Ecosphere 8(4):e01775. 10. 1002/ecs2.1775 Abstract. The generally negative effect of anthropogenic disturbance on the quality of habitats for species viability makes it a common focus of conservation assessment and prioritization efforts. Although many available spatial models and metrics (e.g., distance to or density of disturbance) characterize impact patterns of anthropogenic disturbance on the landscape, a general evaluation of model performance against empirical measurements of ecological integrity is lacking. We tested both distancebased and disturbance-density models in relation to ecological indicators. The models included roads, residential and commercial development, agricultural land use, mining, energy development infrastructure, and transmission structures as disturbance sources. Model parameters were based on expert input and results from the published literature. The disturbance models were tested against two disparate and independent measures of habitat quality: a floristic quality index and measures of greater sagegrouse population integrity. Floristic quality scores were significantly lower in vegetation plots closer to disturbances in a general distance-based disturbance model across Colorado. Although the proportion of variation in floristic quality explained by anthropogenic disturbance was relatively low (8.5-11.8%), it appeared to represent a ubiquitous baseline negative effect of proximity to anthropogenic disturbance on the quality of vegetation communities. For both distance-and density-based greater sage-grouse models, modeled disturbance indices were significantly lower (10-12 times) near active than historic leks, and numbers of males counted at leks increased significantly (3.2-3.4 times) as modeled disturbance decreased. Our findings indicate that as a general class, geospatial models can depict effects of anthropogenic disturbance on both plant communities and individual animal species. Empirical validation of disturbance models focused on other species or regions is recommended to further evaluate the utility and reliability of these methods.

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Climate change vulnerability assessment is a key first step for land managers attempting to address the potential impacts of future climatic conditions on important vegetation types. We compared outcomes of three vulnerability assessments focused on major vegetation types in Colorado. Assessments differed in methods and scale, but overlapped in both qualitative and quantitative techniques, and in vegetation types assessed. Agreement on vegetation type vulnerability was 47-50% between the regional scale southwestern Colorado assessment and either of two statewide assessments. Disagreements were due to regional sampling bias, qualitative vs. quantitative climate exposure analysis, or lack of information about the vegetation type in question. The two statewidescale assessments were in agreement on 75% of vegetation types assessed in both studies; differences were due to choice and interpretation of climate projection data. Sources of variation are categorized in relation to a taxonomy of uncertainty. We compare our iterative experience of climate change vulnerability assessment using methods adapted to the needs and means of various land management agencies to the technique of triangulation used to gradually home in on the location of an object. We clarify ways in which participant choices shape the end result and mitigate the common perception that climate science is too difficult for the lay person to use or understand.