Carol C. Horvitz

Smithsonian Institution, Washington, Washington, D.C., United States

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Publications (35)134.37 Total impact

  • 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.
    Proceedings of the National Academy of Sciences 03/2014; · 9.74 Impact Factor
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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.
    Journal of Ecology 06/2013; · 5.43 Impact Factor
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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.
    International Journal of Complex Systems in Science. 12/2012; 2(1):1-5.
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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.
    Ecology and Evolution 07/2012; 2(7):1446-57. · 1.18 Impact Factor
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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.
    Experimental gerontology 06/2012; 47(10):773-81. · 3.34 Impact Factor
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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.
    Perspectives in Plant Ecology Evolution and Systematics 01/2012; 14:231-241. · 4.16 Impact Factor
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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.
    Journal of Evolutionary Biology 01/2012; 25(1):38-53. · 3.48 Impact Factor
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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.
    Ecological Applications 07/2011; 21(5):1604-16. · 3.82 Impact Factor
  • 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.
    Journal of Animal Ecology 04/2011; 80(5):976-89. · 4.84 Impact Factor
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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.
    Theoretical Population Biology 04/2011; 80(1):1-15. · 1.24 Impact Factor
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    John L. Maron, Carol C. Horvitz, Jennifer L. Williams
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    ABSTRACT: Summary1. Despite a large literature documenting the effects of mutualists and/or antagonists on plant performance, we still have limited insight into the strength of these interactions, as this involves quantifying how one species influences the population dynamics of another.2. Here, we use data from two example systems, Cynoglossum officinale and Calathea ovandensis, to illustrate how experiments, demographic data and stage-based population models can be combined to estimate interaction strength of insect herbivores on plants. Because many plant populations may not be at equilibrium, we conduct transient analyses and contrast these results to more traditional asymptotic results.3. We calculate three metrics of interaction strength, Δλasymptotic, the change in asymptotic annual per capita plant population growth rate resulting from herbivore exclusion, Δλ(t), the change in transient λ caused by herbivores at t = M (where M = the time of their maximum effect during the transient phase) and Δλtransient, a time-averaged effect of consumers on λ across the entire transient phase.4. Fairly strong impacts of insect consumers on plant fecundity do not translate similarly to Δλasymptotic. Results show that Δλ(t) can be larger (or smaller) than Δλasymptotic but in our examples Δλtransient was similar in magnitude to Δλasymptotic.5. The transient effects of consumers on λ were driven by changes in the elasticity of fecundity across the transient phase. These effects were dynamic even though consumer impacts on demography and vital rates were held constant. The importance of particular stages and transitions to annual population growth vary during the transient phase.6.Synthesis. We describe three metrics of interaction strength, Δλasymptotic, Δλ(t) and Δλtransient. These metrics have several advantages over more commonly used trait or performance measures that quantify the outcome of interactions. We illustrate how the transient impacts of consumers on λ are dynamic, with the changing stage distribution of a population and transient elasticities driving these effects. More generally, this study shows that the impacts of animals on plant performance do not translate equivalently to plant population growth, thereby underscoring the importance of using population models to extend the inference of individual-level experiments.
    Journal of Ecology 02/2010; 98(2):290 - 301. · 5.43 Impact Factor
  • Carol C. Horvitz, Johan Ehrlén, David Matlaga
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    ABSTRACT: Summary1. In the understorey herb Lathyrus vernus seed production is pollen limited, but increased reproduction results in a lower probability of remaining reproductive. Putting these two results together, previous research reported that population growth rate λ was negatively impacted by high pollination.2. Thus, costs and benefits have to be translated into the common currency of their respective effects on population dynamics to determine whether populations are truly pollen limited or whether they are already at an optimal level of pollination.3. Also, when pollinators and demography vary from year to year we require a framework that examines reproductive benefits and demographic costs in the context of a variable environment. Whether or not additional pollination will increase the stochastic population growth rate λS depends upon the balance of stochastic elasticities of the costs and benefits.4. In constant environment models, where seed survival, germination and seedling survival were increased, we found that the high cost of reproduction could be offset by improvements in seed survival and germination, but not by improvements of seedling survival.5. In variable environment models, where changes in the sequence and frequencies of high- and low-pollination years mixed with occasional high-germination years were modelled, we found that increasing the frequency of high-germination conditions could offset the cost of reproduction, and the offset was even greater if high-germination years occurred after a high-pollination year or if high pollination was accompanied by high-germination conditions in the same year.6. Both deterministic λ and stochastic λS were less sensitive to perturbation of reproduction than to perturbation of the probability for flowering plants to remain reproductive. In other words, a small change in the parameter which is related to the ‘cost’ of reproduction had a bigger effect than a small change in the parameter which is related to the ‘benefit’ of increased pollination for Lathyrus.7.Synthesis. Stochastic environment-specific elasticities for reproduction and stasis of flowering plants differ in their response to environmental context. The cost–benefit relationships, the ultimate fitness consequences of supplemental pollen, are influenced by the frequency and sequence of years differing in pollen availability and recruitment conditions.
    Journal of Ecology 01/2010; 98(2):268 - 278. · 5.43 Impact Factor
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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.
    International Journal of Plant Sciences 01/2010; 13(6):945-959. · 1.54 Impact Factor
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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.
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    ABSTRACT: In tropical rain forests, rates of forest turnover and tree species' life-history differences are shaped by the life expectancy of trees and the time taken by seedlings to reach the canopy. These measures are therefore of both theoretical and applied interest. However, the relationship between size, age, and life expectancy is poorly understood. In this paper, we show how to obtain, in a dynamic environment, age-related population parameters from data on size and light transitions and survival of individuals over single time steps. We accomplish this goal by combining two types of analysis (integral projection modeling and age-from-stage analysis for variable environments) in a new way. The method uses an index of crown illumination (CI) to capture the key tree life-history axis of movement through the light environment. We use this method to analyze data on nine tropical tree species, chosen to sample two main gradients, juvenile recruitment niche (gap/nongap) and adult crown position niche (subcanopy, canopy-emergent). We validate the method using independent estimates of age and size from growth rings and 14C from some of the same species at the same site and use our results to examine correlations among age-related population parameters. Finally, we discuss the implications of these new results for life histories of tropical trees.
    Ecology 10/2009; 90(10):2766-78. · 5.18 Impact Factor
  • Carlos García-Robledo, Carol C. Horvitz
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    ABSTRACT: Leaf volatile chemicals are known to reduce herbivory rates by repelling or intoxicating insect herbivores and by attracting the predators and parasitoids of herbivores. However, leaf volatiles may also be used by insect herbivores as cues to locate their host plants. Leaf volatiles are suggested to be important host search cues for herbivores in structurally complex and diverse habitats, such as tropical rain forests. A group of insect herbivores, the rolled-leaf beetles (Coleoptera: Chrysomelidae: Hispinae), have maintained a highly specialized interaction with Neotropical gingers (Zingiberales) for ca. 60 million years. In this study, we explored chemical attraction to host plants under controlled laboratory conditions, using four sympatric rolled-leaf beetle species, Cephaloleia dorsalis Baly, Cephaloleia erichsonii Baly, Cephaloleia fenestrata Weise, and Cephaloleia placida Baly. For each beetle species, we investigated (i) whether it was repelled or attracted by leaf scents produced by four host and four non-host plant species, including Neotropical gingers in the families Marantaceae, Costaceae, and Zingiberaceae; and (ii) its ability to use scents to detect its host plant. We found that rolled-leaf beetles can detect and are attracted by leaf volatiles from both host and non-host gingers. Additionally, when beetles were simultaneously exposed to leaf volatiles from host and non-host plants, three rolled-leaf beetle species were significantly more attracted by volatiles from their host plants than from non-hosts. Only one of the beetle species was not able to discriminate between host and non-host scents.
    Entomologia Experimentalis et Applicata 03/2009; 131(2):115 - 120. · 1.53 Impact Factor
  • David P Matlaga, Carol C Horvitz
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    ABSTRACT: Sexually and clonally produced offspring may respond to environmental heterogeneity by growing and surviving at different rates. In forest understories, the availability of light ranges from low in shaded, closed canopy to high in tree-fall gaps. We experimentally investigated the growth and survival of both types of offspring in three treatments (gap centers, gap edges, and shaded understory) over 16 months. We expected the demographic performance of both types of offspring to be highest in the centers of gaps and lowest in the shaded understory. However, we expected seedlings to be more sensitive to the gradient in light (larger difference in growth and survival between light levels) than vegetative offspring because of their small size and lack of connection to maternal resources. Both offspring types grew fastest and obtained their largest sizes in gap centers. Contrary to our expectations, offspring types differed in which light conditions favored highest survival. Seedlings survived best in gap centers, while vegetative offspring had their highest survival in the shaded understory. In agreement with our hypothesis, survival and growth of seedlings were more sensitive to light availability, showing a large difference in growth and survival between light levels, compared to vegetative offspring.
    American Journal of Botany 02/2009; 96(2):439-47. · 2.59 Impact Factor
  • Carol C Horvitz, Shripad Tuljapurkar
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    ABSTRACT: Mortality plateaus at advanced ages have been found in many species, but their biological causes remain unclear. Here, we exploit age-from-stage methods for organisms with stage-structured demography to study cohort dynamics, obtaining age patterns of mortality by weighting one-period stage-specific survivals by expected age-specific stage structure. Cohort dynamics behave as a killed Markov process. Using as examples two African grasses, one pine tree, a temperate forest perennial herb, and a subtropical shrub in a hurricane-driven forest, we illustrate diverse patterns that may emerge. Age-specific mortality always reaches a plateau at advanced ages, but the plateau may be reached rapidly or slowly, and the trajectory may follow positive or negative senescence along the way. In variable environments, birth state influences mortality at early but not late ages, although its effect on the level of survivorship persists. A new parameter micro omega summarizes the risk of mortality averaged over the entire lifetime in a variable environment. Recent aging models for humans that employ nonobservable abstract states of "vitality" are also known to produce diverse trajectories and similar asymptotic behavior. We discuss connections, contrasts, and implications of our results to these models for the study of aging.
    The American Naturalist 02/2008; 172(2):203-15. · 4.55 Impact Factor
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    ABSTRACT: Both means and year-to-year variances of climate variables such as temperature and precipitation are predicted to change. However, the potential impact of changing climatic variability on the fate of populations has been largely unexamined. We analyzed multiyear demographic data for 36 plant and animal species with a broad range of life histories and types of environment to ask how sensitive their long-term stochastic population growth rates are likely to be to changes in the means and standard deviations of vital rates (survival, reproduction, growth) in response to changing climate. We quantified responsiveness using elasticities of the long-term population growth rate predicted by stochastic projection matrix models. Short-lived species (insects and annual plants and algae) are predicted to be more strongly (and negatively) affected by increasing vital rate variability relative to longer-lived species (perennial plants, birds, ungulates). Taxonomic affiliation has little power to explain sensitivity to increasing variability once longevity has been taken into account. Our results highlight the potential vulnerability of short-lived species to an increasingly variable climate, but also suggest that problems associated with short-lived undesirable species (agricultural pests, disease vectors, invasive weedy plants) may be exacerbated in regions where climate variability decreases.
    Ecology 02/2008; 89(1):19-25. · 5.18 Impact Factor
  • Journal of Ecology 09/2007; 95(6):1370 - 1380. · 5.43 Impact Factor

Publication Stats

621 Citations
134.37 Total Impact Points


  • 2012
    • Smithsonian Institution
      Washington, Washington, D.C., United States
  • 2006–2012
    • Stanford University
      • Department of Biology
      Palo Alto, CA, United States
  • 1999–2012
    • University of Miami
      • Department of Biology
      Coral Gables, FL, United States
  • 2011
    • University of Oxford
      • Department of Statistics
      Oxford, ENG, United Kingdom