Carol C. Horvitz

University of Miami, كورال غيبلز، فلوريدا, Florida, United States

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Publications (64)267.06 Total impact

  • Andrea C Westerband · Carol C Horvitz
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    ABSTRACT: PREMISE OF THE STUDY: For tropical forest understory plants, the ability to grow, survive, and reproduce is limited by the availability of light. The extent to which reproduction incurs a survival or growth cost may change with light availability, plant size, and adaptation to shade, and may vary among similar species. METHODS: We estimated size-specifi c rates of growth, survival, and reproduction (vital rates), for two neotropical understory herbs (order Zingiberales) in a premontane tropical rainforest in Costa Rica. During three annual censuses we monitored 1278 plants, measuring leaf area, number of inflorescences, and canopy openness. We fit regression models of all vital rates and evaluated them over a range of light levels. The best fitting models were selected using Akaike’s Information Criterion. KEY RESULTS: All vital rates were significantly influenced by size in both species, but not always by light. Increasing light resulted in higher growth and a higher probability of reproduction in both species, but lower survival in one species. Both species grew at small sizes but shrank at larger sizes. The size at which shrinkage began differed among species and light environments. Vital rates of large individuals were more sensitive to changes in light than small individuals. CONCLUSIONS: Increasing light does not always positively influence vital rates; the extent to which light affects vital rates depends on plant size. Differences among species in their abilities to thrive under different light conditions and thus occupy distinct niches may contribute to the maintenance of species diversity.
    No preview · Article · Aug 2015 · American Journal of Botany
  • Kelley D. Erickson · Anthony L. Koop · Carol C. Horvitz
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    ABSTRACT: Interest in spatial population dynamics includes applications to the spread of disease and invasive species. Recently, models for structured populations have been extended to incorporate temporal variation in both demography and dispersal. Here we propose a novel version of the model that incorporates structured dispersal to evaluate how changes in the relative proportion of mammalian, and short- and long-distance avian dispersers affect the rate of spread of an invasive shrub, Ardisia elliptica in Everglades National Park. We implemented 45 time-invariant models, including one in which a single dispersal kernel was estimated from field data by pooling all seedlings, and 44 that were disperser-structured in which dispersal kernels were estimated separately for gravity-, catbird-, robin- and raccoon-dispersed seed. Robins, the longest distance dispersers, are infrequent. Finally we implemented a timevarying model that included variability among years in the proportion of seeds that were taken by robins. The models estimated invasion speeds that ranged from 3.9 to 34.7 m yr-1. Infrequent long-distance dispersal by robins were important in determining invasion speed in the disperser-structured model. Comparing model projections with the (historically) known rate of spread, we show how a model that stratifies seeds by dispersal agents does better than one that ignores them, although all of our models underestimate it.
    No preview · Article · Aug 2015 · Discrete and Continuous Dynamical Systems - Series B
  • David P Matlaga · Carol C Horvitz
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    ABSTRACT: • Sexual reproduction is often associated with a cost in terms of reduced survival, growth, or future reproduction. It has been proposed that plant size and the environment (availability of key resources) can sometimes lower or even nullify the cost of reproduction.• We address this issue experimentally with the Neotropical herb Goeppertia marantifolia, by manipulating sexual reproductive effort and measuring the demographic performance of plants and of their clonal offspring, in the context of natural variation in light availability.• Plants in the high-reproductive-effort treatment grew less between seasons but did not differ in their probability of flowering the second season or in inflorescence size compared with plants in the low-effort treatment. Reproductive effort of parent plants influenced the leaf area of their clonal offspring. Plants that invested less in sexual reproduction produced clonal offspring that were initially larger than those produced by plants that invested more in reproduction. The magnitude of this effect was greater in parent plants that received two seasons of the manipulated reproductive effort than in those that received a single season. The trade-off between reproductive modes dampened with time, leading to smaller differences in clonal offspring leaf area between treatments over time.• We found evidence of a cost of reproduction and trade-offs between reproductive modes, although the magnitude of these costs was small. However, we found no evidence of lower costs of reproduction for larger plants or for plants in higher-light environments over our 2-yr study period. © 2015 Botanical Society of America, Inc.
    No preview · Article · Mar 2015 · American Journal of Botany
  • Robert M. McElderry · Mark H. Salvato · Carol C. Horvitz
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    ABSTRACT: Population viability analyses for butterflies typically use metapopulation models, but for endemic species with no redundancy among subpopulations, we need to understand local population dynamics. However, little is known about the sensitivity of butterfly population vital rates and viability to disturbances such as fire. We fit quadratic models to monthly butterfly count data (1999–2014) to estimate an annual population density index that represents density during peak abundance each year. Relative population growth rate was estimated using a time series of the population density index, and population dynamics parameters r 0 and K were estimated by fitting relative growth rates (RGRs) to density independent and dependent models that include the effects of fire. Population models were simulated 20 and 100 years into the future to evaluate the sensitivity of extinction probability to density dependent dynamics and fire. Although the density independent model had the highest relative likelihood, density dependent models produced population trajectories with behavior more congruent with data from the Anaea troglodyta floridalis population. The absence of fire increased sensitivity of RGR to density, and the occurrence of fire buffered this sensitivity by increasing carrying capacity. Extinction risk was most sensitive to the inclusion of density dependent dynamics. Density dependent models provided a more optimistic outlook relative to density independent models (8 vs. 66 % probability of extinction in 20 years). Our simulations suggest that improving carrying capacity would provide the best buffer to extinction for this endangered endemic butterfly.
    No preview · Article · Feb 2015 · Biodiversity and Conservation
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    ABSTRACT: Background/Question/Methods Natural populations employ different strategies for persisting in disturbed environments. Given prevalent disturbance in both natural and managed settings, it is important to understand life history adaptations that mediate population persistence and species coexistence in variable environments. How do we distinguish strategies for persisting under frequent fire disturbance? What can we learn about disturbance-adaptation from the responses of populations to frequent burning? We examine demographic data on five sympatric woody plant species growing in the Brazilian cerradoand analyze demographic responses to fire frequency as indicators of life-history adaptations to frequent fire disturbance. We apply Markov chain theory to investigate how fire frequency affects life expectancy and age schedules of development, and we use these responses to as demographic diagnostics to characterize species as either ‘demographically resistant’ or ‘demographically resilient’ with respect to fire disturbance. ------------------------- Results/Conclusions ‘Demographically resistant’ species are those that are strongly influenced by fire and must reach a threshold size to escape fire-induced mortality. ‘Demographically resilient’ species are those that are relatively insensitive to fire in terms of mortality and rebound after fire by taking advantage of the transient opportunities afforded by nutrient releases and reduced competition during early succession post-fire. The former succeed by retaining biomass and the latter succeed by renewing it. Species vary in how their longevity and developmental rates respond to increasing frequency of disturbance. Life expectancy of resistant species is strongly influenced by fire frequency; these species rely on vegetative reproduction or very high seed production for persistence. Life expectancy and developmental rates of resilient species are relatively indifferent to fire frequency and because they are under less pressure to escape fire-induced mortality, they may allocate more resources to reproduction during early-succession. Such inter-specific variation in life history is predictive of population structure, species persistence and community composition under distinct disturbance scenarios. We suggest that the distinction between demographically resistant and demographically resilient among Brazilian cerrado species may be generalizable as two distinct modes of persistence in the face of disturbance.
    No preview · Conference Paper · Aug 2014
  • Susan Kalisz · Rachel B Spigler · Carol C Horvitz
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    ABSTRACT: A major goal in ecology is to understand mechanisms that increase invasion success of exotic species. A recent hypothesis implicates altered species interactions resulting from ungulate herbivore overabundance as a key cause of exotic plant domination. To test this hypothesis, we maintained an experimental demography deer exclusion study for 6 y in a forest where the native ungulate Odocoileus virginianus (white-tailed deer) is overabundant and Alliaria petiolata (garlic mustard) is aggressively invading. Because population growth is multiplicative across time, we introduce metrics that correctly integrate experimental effects across treatment years, the cumulative population growth rate, λc, and its geometric mean, λper-year, the time-averaged annual population growth rate. We determined λc and λper-year of the invader and of a common native, Trillium erectum. Our results conclusively demonstrate that deer are required for the success of Alliaria; its projected population trajectory shifted from explosive growth in the presence of deer (λper-year = 1.33) to decline toward extinction where deer are excluded (λper-year = 0.88). In contrast, Trillium's λper-year was suppressed in the presence of deer relative to deer exclusion (λper-year = 1.04 vs. 1.20, respectively). Retrospective sensitivity analyses revealed that the largest negative effect of deer exclusion on Alliaria came from rosette transitions, whereas the largest positive effect on Trillium came from reproductive transitions. Deer exclusion lowered Alliaria density while increasing Trillium density. Our results provide definitive experimental support that interactions with overabundant ungulates enhance demographic success of invaders and depress natives' success, with broad implications for biodiversity and ecosystem function worldwide.
    No preview · Article · Mar 2014 · Proceedings of the National Academy of Sciences
  • Susan Kalisz · Rachel B. Spigler · Carol Horvitz
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    ABSTRACT: Background/Question/Methods In forest and rangeland ecosystems across the globe, the domination of native plant communities by exotic species and declines in biodiversity are becoming widespread crises. Strong interactions between resident native species and invading exotics are thought to reduce the spread and establishment of exotics (biotic resistance), with increasing recognition of the context-dependence of this outcome. One key context is the abundance of herbivores. A recent hypothesis implicates high ungulate herbivore numbers as a cause of disrupted species interactions, driving native plant declines and exotic plant domination. Tests of this hypothesis require empirical evidence of the quantitative effect of herbivores on the fitness of both natives and exotics, indicated by the ultimate metric, per capita population growth rate, but such studies are rare. We tested this hypothesis directly with a six-year replicated deer-exclusion experiment in a forest where Odocoileus virginianus (white-tailed deer) is overabundant and Alliaria petiolata (garlic mustard) is aggressively invading. We applied novel multi-year projection-matrix analyses to data on the common herbaceous native Trillium erectum and the invader Alliaria. Results/Conclusions With deer, Alliaria maintained explosive population growth rates (λper-year=1.33) and high densities, while Trillium reproduction and λper-year (1.04) were suppressed relative to plots where deer were excluded. Without deer, Alliaria’s population growth rate plummeted (λper-year =0.88) and densities became low, while Trillium reproduction and population growth rate (λper-year =1.20) increased dramatically. Other native herbaceous perennials showed similar responses to Trillium. Multi-year retrospective sensitivity analyses revealed that the difference in Trillium’s λper-year between deer-exclusion and deer-access treatments was largely due to positive contributions (cij) by the flowering stage. In contrast, all aspects of the Alliaria’s life cycle are stifled where deer are excluded; every matrix element made negative contributions to the difference in fitness between treatments. These findings support the hypothesis that overabundant ungulates disrupt competition between native and exotic plants. Where deer are excluded, native plants recover, restoring their ability to compete with Alliaria and driving Alliaria’s decline. Since Alliaria cannot thrive without the facilitative effects of deer, our results suggest that previous explanations for this exotic’s success (e.g. novel weapons) may be context dependent. If these results apply generally, then reducing ungulate numbers where they are overabundant will be key for curbing invasion success in forests and rangelands worldwide.
    No preview · Conference Paper · Aug 2013
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    ABSTRACT: 1. Selectively harvesting whole individuals in managed populations (e.g. fisheries, hunting) has substantial effects on life expectancy and age at maturity. Although demographic rates of trees are impacted by recurrent harvest of plant organs (e.g. fruit, leaf, bark) known as non-timber forest products, the effect of such harvesting on life history traits is less explored. 2. Here, we investigate how different strategies of foliage and bark harvest by local people affect life expectancy and age at maturity of Khaya senegalensis across two climatic regions in West Africa. We compare elasticities of life expectancy to perturbation of vital rates to the elasticities of population growth rate, emphasizing how the two kinds of elasticity address distinct biological issues and management goals. 3. Life expectancy was shorter and reproduction delayed in the dry than in the moist region, indicating a cost of drought to life history traits. Harvesting at constant rates only affects (increased) life expectancy in the moist region and (reduced) age at first reproduction in the dry region. 4. Models in which harvest intensity varies stochastically over time show results similar to those with constant harvesting rate. However, there is an interactive effect of harvest on life history traits between regions. Increasing harvesting pressure accelerates maturity and reduces life expectancy in the dry region but delays reproduction and increases life expectancy in the moist region. This indicates that stochasticity magnifies the effect of harvesting on life history traits. 5. With the notable exception of heavily harvested populations in the moist region, life expectancy is more elastic to survival of early rather than late life stages. This pattern contrasts with the elasticity of population growth rate; the latter is more elastic to survival of late rather than early life stages. 6. Synthesis. Our results suggest that plant harvesting can affect life history traits but in different ways across an environmental gradient. Failure to account for stochasticity in harvesting rate can mask some of these effects. Our results also indicate that processes driving plant life expectancy, at least for long-lived species, may differ from those driving population dynamics.
    Full-text · Article · Jun 2013 · Journal of Ecology
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    Carmen Coll · Carol C. Horvitz · Robert McElderry
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    ABSTRACT: The Florida leafwing is an endemic butterfly which is distributed in South Florida and the lower Keys. Stage-structured population models are a useful tool for the management and conservation of Florida leafwing. In this work we use a discrete-time periodic control system for describing a leafwing population. One of the main differences between this model and classical stage-structured models is that in the current model we can alter the number of adults contributing to eggs production. This allows us to control the population. The solution of the problem is obtained using invariant formulations of positive periodic systems.
    Full-text · Article · Dec 2012
  • Orou G. Gaoue · Carol Horvitz
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    ABSTRACT: Background/Question/Methods Two decades of studies on harvest of non-timber forest products (NTFP) from wild populations, a widespread activity worldwide, reveal that harvest of products that are detachable from individuals can impact annual demographic rates and population dynamics. Expected lifespan of individuals and time to reproduction could be important parameters in wild populations that are being managed. While the effect on such traits of selective harvest of whole individuals from populations has been explored recently (e.g. in fisheries, hunting), the effect of harvesting parts from standing individuals on life history traits has been ignored. Here, we examine how the level of foliage and bark harvest by local people affects expected lifespan and age of first reproduction for a tropical tree, Khaya senegalensis across two climatic regions (moist and dry) of Benin, West Africa. We also compare the sensitivity of life expectancy to transitions across the life-cycle under different harvest and climate regimes, employing recently introduced concepts and methods. Results/Conclusions The effect of harvest on life history traits differed between regions. Individual trees are expected to reproduce earlier but live longer in the moist than in the dry region. In the moist region, age at first reproduction is not affected very much by harvest, while life expectancy is affected considerably with a positive association between level of harvest and length of life. In the dry region, harvest affects age at first reproduction but not life expectancy and high levels of harvest are associated with early reproduction. Life expectancy is more sensitive to survival than to growth or retrogression. With the notable exception of populations in the moist region that are heavily harvested, life expectancy is more sensitive to survival of early rather than late life stages. This pattern contrasts with our previous results; we found that population growth rate, a parameter that is distinct from expected life span, was more sensitive to survival of late rather than early life stages. Models in which harvest level varies stochastically over time show an interaction effect between the initial harvest level and the frequency of harvest during the lifetime of the cohort. The nature of the interaction differed by region as well as between life history traits. Our findings suggest that the processes driving plant life expectancy, at least for long-lived species, may differ from those driving population dynamics. Our results also underscore that climatic differences may override the effects of NTFP harvest on life history traits.
    No preview · Conference Paper · Aug 2012
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    Carlos García-Robledo · Carol C Horvitz
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    ABSTRACT: SPECIALIZATION OF INSECT HERBIVORES TO ONE OR A FEW HOST PLANTS STIMULATED THE DEVELOPMENT OF TWO HYPOTHESES ON HOW NATURAL SELECTION SHOULD SHAPE OVIPOSITION PREFERENCES: The "mother knows best" principle suggests that females prefer to oviposit on hosts that increase offspring survival. The "optimal bad motherhood" principle predicts that females prefer to oviposit on hosts that increase their own longevity. In insects colonizing novel host plants, current theory predicts that initial preferences of insect herbivores should be maladaptive, leading to ecological traps. Ecological trap theory does not take into account the fact that insect lineages frequently switch hosts at both ecological and evolutionary time scales. Therefore, the behavior of insect herbivores facing novel hosts is also shaped by natural selection. Using a study system in which four Cephaloleia beetles are currently expanding their diets from native to exotic plants in the order Zingiberales, we determined if initial oviposition preferences are conservative, maladaptive, or follow the patterns predicted by the "mother knows best" or the "optimal bad motherhood" principles. Interactions with novel hosts generated parent-offspring conflicts. Larval survival was higher on native hosts. However, adult generally lived longer on novel hosts. In Cephaloleia beetles, oviposition preferences are usually associated with hosts that increase larval survival, female fecundity, and population growth. In most cases, Cephaloleia oviposition preferences follow the expectations of the "mothers knows best" principle.
    Preview · Article · Jul 2012 · Ecology and Evolution
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    ABSTRACT: Interest in stage-and age structured models has recently increased because they can describe quantitative traits such as size that are left out of age-only demography. Available methods for the analysis of effects of vital rates on lifespan in stage-structured models have not been widely applied because they are hard to use and interpret, and tools for age and stage structured populations are missing. We present easily interpretable expressions for the sensitivities and elasticities of life expectancy to vital rates in age-stage models, and illustrate their application with two biological examples. Much of our approach relies on trading of time and mortality risk in one stage for time and risk in others. Our approach contributes to the new framework of the study of age- and stage-structured biodemography.
    Full-text · Article · Jun 2012 · Experimental gerontology
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    ABSTRACT: The intermediate disturbance hypothesis (IDH) predicts a hump-shaped pattern between community diversity and disturbance, and is central to understanding patterns of species diversity. Here, we examine IDH in the context of alien plant invasions. IDH can offer insight into the role of disturbance in facilitating plant invasions and the effect of these invasions on floristic diversity. Early stages of succession are most susceptible to invasion because resources and colonisation opportunities are elevated after disturbance. This trend is accentuated by human-mediated dispersal, a bias towards early successional species in the alien species pool, the tendency for fast-growing species to profit most from enemy release, and increased disturbance levels in human-modified habitats. Human disturbance, coupled with plant introductions, extends the diversity–disturbance curve and shifts peak diversity towards higher disturbance levels. However, invasive aliens can reduce native diversity at the community scale, especially in mid succession where competitive interactions structure communities. Certain invasive plants may have higher impacts because they overcome some life history tradeoffs as a result of their association with humans or novel evolutionary histories, e.g. enemy release. This may directly or indirectly (e.g. through plastic reallocation of resources from defence into growth) enable invasive plants to colonise earlier or persist into later stages of succession. By modifying disturbance regimes, invaders that transform the environment may also interfere with succession and precipitate low diversity communities. Low introduction rates of late successional species may currently limit impacts of aliens under infrequent disturbance. IDH is a useful framework for understanding ecological communities. However, because of the novel evolutionary histories of alien species and the anthropogenic context in which they invade, disturbance levels that maximise total diversity in invaded communities can differ from those that maximise native diversity. Joint consideration of IDH and alien invasion patterns suggests a range of strategies can be used to manage diversity.
    Full-text · Article · Jun 2012 · Perspectives in Plant Ecology Evolution and Systematics
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    Carlos García-Robledo · C C Horvitz
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    ABSTRACT: One explanation for the widespread host specialization of insect herbivores is the 'Jack of all trades-master of none' principle, which states that genotypes with high performance on one host will perform poorly on other hosts. This principle predicts that cross-host correlation in performance of genotypes will be negative. In this study, we experimentally explored cross-host correlations and performance among families in four species (two generalist and two specialist) of leaf beetles (Cephaloleia spp.) that are currently expanding their diets from native to exotic plants. All four species displayed similar responses in body size, developmental rates and mortality rates to experimentally controlled diets. When raised on novel hosts, body size of larvae, pupae and adults were reduced. Development times were longer, and larval mortality was higher on novel hosts. Genotype × host-plant interactions were not detected for most traits. All significant cross-host correlations were positive. These results indicate very different ecological and evolutionary dynamics than those predicted by the 'Jack of all trades-master of none' principle.
    Preview · Article · Jan 2012 · Journal of Evolutionary Biology
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    Orou G Gaoue · Carol C Horvitz · Tamara Ticktin
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    ABSTRACT: With increasing reports of overexploitation of wild plants for timber and non-timber forest products, there has been an increase in the number of studies investigating the effect of harvest on the dynamics of harvested populations. However, most studies have failed to account for temporal and spatial variability in the ecological conditions in which these species occur, as well as variability in the patterns of harvest intensity. In reality, local harvesters harvest at variable rather than fixed intensity over time. Here we used Markov chains to investigate how different patterns of harvesting intensity (summarized as return time to high harvest) affected the stochastic population growth rate (lambda(s)) and its elasticity to perturbation of means and variances of vital rates. We studied the effect of bark and foliage harvest from African mahogany Khaya senegalensis in two contrasting ecological regions in Benin. Khaya populations declined regardless of time between harvests of high intensity. Moreover, lambda(s) increased with decreasing harvesting pressure in the dry region but, surprisingly, declined in the moist region toward lambda(s) = 0.956. The stochastic elasticity was dominated by the stasis of juveniles and adults. The declining growth rate with decreasing harvest pressure in the moist region was mainly driven by the declining mean survival rates of juveniles and adults. Our results suggest that modeling the temporal variability of harvest intensity as a Markov chain better mimics local practices and provides insights that are missed when temporal variability in harvest intensity is modeled as independent over time and drawn from a fixed distribution.
    Full-text · Article · Jul 2011 · Ecological Applications
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    Carlos García-Robledo · Carol C Horvitz
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    ABSTRACT: 1. Colonization success of species when confronted with novel environments is of interest in ecological, evolutionary and conservation contexts. Such events may represent the first step for ecological diversification. They also play an important role in adaptive divergence and speciation. 2. A species that is able to do well across a range of environments has a higher plasticity than one whose success is restricted to a single or few environments. The breadth of environments in which a species can succeed is ultimately determined by the full pattern of its vital rates in each environment. 3. Examples of organisms colonizing novel environments are insect herbivores expanding their diets to novel host plants. One expectation for insect herbivores is that species with specialized diets may display less plasticity when faced with novel hosts than generalist species. 4. We examine this hypothesis for two generalist and two specialist neotropical beetles (genus Cephaloleia: Chrysomelidae) currently expanding their diets from native to novel plants of the order Zingiberales. Using an experimental approach, we estimated changes in vital rates, life-history traits and lifetime fitness for each beetle species when feeding on native or novel host plants. 5. We did not find evidence supporting more plasticity for generalists than for specialists. Instead, we found similar patterns of survival and fecundity for all herbivores. Larvae survived worse on novel hosts; adults survived at least as well or better, but reproduced less on the novel host than on natives. 6. Some of the novel host plants represent challenging environments where population growth was negative. However, in four novel plant-herbivore interactions, instantaneous population growth rates were positive. 7. Positive instantaneous population growth rates during initial colonization of novel host plants suggest that both generalist and specialist Cephaloleia beetles may be pre-adapted to feed on some novel hosts. This plasticity in host use is a key factor for successful colonization of novel hosts. Future success or failure in the colonization of these novel hosts will depend on the demographic rates described in this research, natural selection and the evolutionary responses of life-history traits in novel environments.
    Preview · Article · Apr 2011 · Journal of Animal Ecology
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    ABSTRACT: We consider stochastic matrix models for population driven by random environments which form a Markov chain. The top Lyapunov exponent a, which describes the long-term growth rate, depends smoothly on the demographic parameters (represented as matrix entries) and on the parameters that define the stochastic matrix of the driving Markov chain. The derivatives of a-the "stochastic elasticities"-with respect to changes in the demographic parameters were derived by Tuljapurkar (1990). These results are here extended to a formula for the derivatives with respect to changes in the Markov chain driving the environments. We supplement these formulas with rigorous bounds on computational estimation errors, and with rigorous derivations of both the new and old formulas.
    Full-text · Article · Apr 2011 · Theoretical Population Biology
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    ABSTRACT: When both selection and demography vary over time, how can the long-run expected strength of selection on quantitative traits be measured? There are two basic steps in the proposed new analysis: one relates trait values to fitness components, and the other relates fitness components to total fitness. We used one population projection matrix for each state of the environment together with a model of environmental dynamics, defining total fitness as the stochastic growth rate. We multiplied environment-specific, stage-specific mean-standardized selection gradients by environment-specific, stage-specific elasticities of the stochastic growth rate, summing over all relevant life-history and environmental paths. Our two example traits were floral tube length in a rainforest herb and the timing of birth in red deer. For each species, we constructed two models of environmental dynamics, including one based on historical climate records. We found that total integrated selection, as well as the relative contributions of life-history pathways and environments, varied with environmental dynamics. Temporal patterning in the environment has selective consequences. Linking models of environmental change to relevant short-term data on demography and selection may permit estimation of the force of selection over the long term in variable environments.
    Full-text · Article · Nov 2010 · International Journal of Plant Sciences
  • Carlos Garcia-Robledo · Carol C. Horvitz · Charles L. Staines
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    ABSTRACT: The Neotropical genus Cephaloleia Chevrolat, 1837 is comprised of 209 described species. Adults usually feed and mate within the scrolls formed by the young rolled leaves of plants of Neotropical Zingiberales. This paper reports for populations of Cephaloleia belti Baly, C. dilaticollis Baly, C. dorsalis Baly and C. placida Baly at La Selva Biological Station (Costa Rica, Central America) detailed descriptions of: 1. larval and adult diets and diet breadth; 2. egg, larval and pupal morphology; 3. larval development times; 4. dimorphic sexual characteristics; 5. adult longevity; and 6. differences in lifespan between genders. Cephaloleia belti displays the broader diet breadth, feeding on 14 species of three families of Zingiberales. Cephaloleia dilaticollis feeds on nine species of three families of Zingiberales. Cephaloleia dorsalis and C. placida feed on four species of Costaceae and two species of Zingiberaceae, respectively. Time to pupation ranges among species from 32.8 to 59.1 days. In the four Cephaloleia species, adult females are larger than males. Genders display marked sexual dimorphism in the shape of their last abdominal sternite and the pygidium. Longevity of adults ranged from ca. 300 to 390 days. Life expectancy estimates for adult beetles reared in the laboratory ranged from 111.5 to 187.2 days. Male and female adults of C. belti and C. dilaticollis have equivalent life expectancies. However, life expectancy is longer for male C. dorsalis and C. placida.
    No preview · Article · Sep 2010 · Zootaxa
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    Lucero Sevillano · Carol C. Horvitz · Paul D. Pratt
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    ABSTRACT: Multiple insects are commonly introduced as biological control agents to reduce the performance of invasive plants. Little is known about the species-specific contributions of co-existing agents, and about the effects of insect density on the control of invasive plants. Several agents are expected to strengthen the control. The effects of insect type, density, and soil type on seedling survival and growth of the invasive tree Melaleuca quinquenervia were investigated in Florida. The biological control agents are Oxyops vitiosa (weevil) and Boreioglycaspis melaleucae (psyllid). A three-way factorial shade-house experiment was conducted, manipulating weevil density (zero/low/high), psyllid density (zero/low/high), and soil type (organic/sandy). Only high densities of one or both insects combined consistently reduced plant survival or growth; low densities did not. Overall, psyllids had stronger effects than weevils and for some performance parameters, the effects of one insect depended not only on its density but also on the density of the other insect. Interaction effects between insects were sometimes positive (i.e. seedling survival was lowest when both insects were in high densities). In other cases, high densities of only one agent were enough to reduce plant growth. Plants perform better on organic soils than on sandy soils. Weevils were more effective in reducing biomass on organic soils, while psyllids were more effective in reducing survival on sandy soils. Seedlings compensated for damage by producing more leaves, with the highest standing leaf crop at intermediate insect densities. These results show that the effectiveness of biological control on M. quinquenervia seedlings varies with insect species and depends upon insect density and soil type.
    Full-text · Article · May 2010 · Biological Control

Publication Stats

3k Citations
267.06 Total Impact Points

Institutions

  • 1990-2015
    • University of Miami
      • Department of Biology
      كورال غيبلز، فلوريدا, Florida, United States
  • 2012
    • Smithsonian Institution
      Washington, Washington, D.C., United States
  • 1992
    • Universidad Nacional Autónoma de México
      Ciudad de México, Mexico City, Mexico
  • 1984-1988
    • University of Chicago
      • Department of Ecology & Evolution
      Chicago, Illinois, United States
  • 1981
    • Northwestern University
      • Program in Biological Sciences
      Evanston, Illinois, United States