Oswald Schmitz - Profile on Academia.edu (original) (raw)

Papers by Oswald Schmitz

Animal carcass decomposition is an often-overlooked component of nutrient cycles. The importance ... more Animal carcass decomposition is an often-overlooked component of nutrient cycles. The importance of carcass decomposition for increasing nutrient availability has been demonstrated in several ecosystems, but impacts in arid lands are poorly understood. In a protected high desert landscape in Argentina, puma predation of vicuñas is a main driver of carcass distribution. Here, we sampled puma kill sites across three habitats (plains, canyons, and meadows) to evaluate the impacts of vicuña carcass and stomach decomposition on soil and plant nutrients up to 5 years after carcass deposition. Soil beneath both carcasses and stomachs had significantly higher soil nutrient content than adjacent reference sites in arid, nutrient-poor plains and canyons, but not in moist, nutrient-rich meadows; stomachs had greater effects on soil nutrients than carcasses. These patterns did not translate into higher plant N concentrations at kill sites, though such responses could have occurred immediately following carcass deposition, which our study did not capture. The biogeochemical effects of puma kills persisted for several years and increased over time, indicating that kills do not create ephemeral nutrient pulses, but can have lasting effects on the distribution of soil nutrients. Comparison to broader spatial patterns of predation risk reveals that puma predation of vicuñas is more likely in nutrient-rich sites, but carcasses have the greatest effects on soil nutrients in nutrient-poor environments, such that carcasses increase localized heterogeneity by generating nutrient hotspots in less productive environments. Predation and carcass decomposition may thus be important overlooked factors influencing ecosystem functioning in arid environments.

Oikos, Nov 1, 2004

This article compares indirect trait-mediated interactions in simple resource Á/ consumer Á/preda... more This article compares indirect trait-mediated interactions in simple resource Á/ consumer Á/predator food webs with those that are density-mediated. It focuses on two well documented responses of consumers to predation risk: decrease in consumer activity and habitat switch. These behavioral effects are transmitted to resources and they cause similar indirect effects as those which are mediated by density changes in consumers. Two indirect interactions are studied in this article: trophic cascades, and apparent competition. Results for density only, trait only and combined density and trait mediated interactions are compared and discussed with respect to manipulation with predator density (top-down manipulation) and resource environmental capacity (bottom-up manipulation). The article shows that trait-mediated, effects on species equilibrial densities are similar to those of density-mediated, but they are often highly non-linear. Thus, they may have potential for even stronger impact on food webs than those which are density mediated.

Frontiers in Behavioral Neuroscience, Apr 17, 2023

Consumer-resource population models drive progress in predicting and understanding predation. How... more Consumer-resource population models drive progress in predicting and understanding predation. However, they are often built by averaging the foraging outcomes of individuals to estimate per capita functional responses (functions that describe predation rate). Reliance on per-capita functional responses rests on the assumption that that individuals forage independently without affecting each other. Undermining this assumption, extensive behavioral neuroscience research has made clear that facilitative and antagonistic interactions among conspecifics frequently alter foraging through interference competition and persistent neurophysiological changes. For example, repeated social defeats dysregulates rodent hypothalamic signaling, modulating appetite. In behavioral ecology, similar mechanisms are studied under the concept of dominance hierarchies. Neurological and behavioral changes in response to conspecifics undoubtedly play some sort of role in the foraging of populations, but modern predator-prey theory does not explicitly include them. Here we describe how some modern approaches to population modeling might account for this. Further, we propose that spatial predator-prey models can be modified to describe plastic changes in foraging behavior driven by intraspecific interaction, namely individuals switching between patches or plastic strategies to avoid competition. Extensive neurological and behavioral ecology research suggests that interactions among conspecifics help shape populations' functional responses. Modeling interdependent functional responses woven together by behavioral and neurological mechanisms may thus be indispensable in predicting the outcome of consumer-resource interactions across systems.

Evolutionary Ecology, Mar 22, 2016

The ability of species to tolerate a warming climate has important implications for ecological fu... more The ability of species to tolerate a warming climate has important implications for ecological functioning. Theory and empirical synthesis suggest species adapted to more thermally variable climates are more capable of acclimating to rising temperatures, and are therefore characterized by greater phenotypic plasticity, than species adapted to less thermally variable environments. But this pattern has not been extensively evaluated for populations within a species that may inhabit different parts of a thermal gradient. In addition, it remains unclear whether different populations with different thermal sensitivities will maintain the same functional ecological roles as thermal regimes shift. To address this question, we conducted a reciprocal transplant experiment using Melanoplus femurrubrum grasshopper populations from Connecticut and Vermont, USA. During summer, the Vermont site was 3 °C cooler on average with 1.5-fold greater temperature variation than the Connecticut site. We measured thermal sensitivity (metabolic rate Q 10 ) of individuals from each population reared in home field and transplanted sites and the nature and strength of trophic interactions with grasses and goldenrod (Solidago). Both grasshopper populations exhibited plasticity, but Q 10 of both populations at Vermont was 1.5-fold broader than populations at the Connecticut site. All grasshoppers had similar survivorship but not similar effects on plants, exhibiting stronger effects on grasses in their home fields relative to their transplanted sites. Only Vermont grasshoppers transplanted to Connecticut significantly impacted Solidago. The study shows populations may physiologically acclimate quickly under new thermal conditions, suggesting stronger tolerance to change than often presumed. But, thermal acclimatization may not translate into the maintenance of a species' functional role. The work underscores the need to link analyses of physiological performance with ecological function to obtain a complete picture of climate change effects on communities.

Multivariate Climate Change Can Favor Large Herbivore Body Size in Food Webs

The American Naturalist, Mar 1, 2018

Climate change is expected to favor smaller-bodied organisms through effects of temperature on ph... more Climate change is expected to favor smaller-bodied organisms through effects of temperature on physiological performance and food-web interactions, so much so that smaller body size has been touted as a universal response to global warming alongside range shifts and changing phenology. However, climate change involves more than warming. It is multivariate, and the interplay between climate variables may result in less straightforward predictions. We present a model that considers the simultaneous effect of multiple variables (temperature, CO2, and moisture) on herbivore body sizes within a tritrophic food web comprised of vegetation, herbivores, and a shared predator. The model accounts for climate effects on animal behavior, plant and animal metabolism, and plant quality to explore emergent effects on herbivore body size. Our analysis reveals that some common multivariate climate change scenarios may favor larger-bodied herbivores, challenging previous findings of shifts toward small-bodied herbivores in the face of rising temperatures.

Scientific Reports, Apr 13, 2023

An important challenge in the study of ecosystem function is resolving how plant antiherbivore ch... more An important challenge in the study of ecosystem function is resolving how plant antiherbivore chemical defence expression may influence plant-associated microbes, and nutrient release. We report on a factorial experiment that explores a mechanism underlying this interplay using individuals of the perennial plant Tansy that vary genotypically in the chemical content of their antiherbivore defenses (chemotypes). We assessed to what extent soil and its associated microbial community versus chemotype-specific litter determined the composition of the soil microbial community. Microbial diversity profiles revealed sporadic effects of chemotype litter and soil combinations. Soil source and litter type both explained the microbial communities decomposing the litter with soil source having a more important effect. Some microbial taxa are related to particular chemotypes, and thus intraspecific chemical variation of a single plant chemotype can shape the litter microbial community. But we found that ultimately the effect of fresh litter inputs from a chemotype appeared to act secondary as a filter on the composition of the microbial community, with the primary factor being the existing microbial community in the soil.

Forest Ecology and Management, Sep 1, 2018

Maintaining white spruce (Picea glauca (Moench) Voss) in mixture with trembling aspen (Populus tr... more Maintaining white spruce (Picea glauca (Moench) Voss) in mixture with trembling aspen (Populus tremuloides Michx.) and other broadleaf competitors following timber harvest in boreal and sub-boreal mixed-wood stands is challenging. Under-planting spruce within harvest gaps is one potential strategy, but it's unclear which gap environments favor spruce in relation to aspen. Here we test the effect of gap position and woody release treatment on leaf area development and growth physiology of spruce and aspen. Five positions were measured from the southern understory through the gap center to the northern understory in replicated strip cuts. The woody release treatment cut all stems around spruce including aspen in subplots within each experimental gap; other subplots were left un-cut for comparison. We measured leaf area per wet weight, leaf photosynthesis, stomatal conductance, and transpiration in low-and full-light conditions. We also assessed photosynthetic plasticity in relation to light. Overall, aspen maintained higher leaf area per unit wet weight than spruce, but spruce leaf area was more sensitive to changes in gap position. Aspen also maintained higher photosynthesis and transpiration rates than spruce under both light conditions, and woody release treatment. The magnitude of difference in gas exchange rates between the two species, however, depended significantly on woody release treatment and gap position for photosynthesis, and on gap position for transpiration. Photosynthetic plasticity was not significantly different across species, gap position, or woody release treatment. Our results indicate that in order to ensure the competitive advantage of spruce in mixed-wood boreal stands, forest managers should concentrate spruce planting and competition control efforts in the centers of canopy openings.

Evolutionary Ecology Research, 1999

This article examines the effect of risk of mortality on the optimal diet of an animal foraging f... more This article examines the effect of risk of mortality on the optimal diet of an animal foraging for two food types. The foods are characterized by different nutritional or energetic values per unit volume, and the forager has constraints on both the amount of time it has available for foraging and on the volume of food that can be processed per unit time. Such a situation characterizes the diet choice problem faced by many herbivores. The two food types may occur in the same habitat, or they may occur in different habitat patches; in the latter case, they cannot be encountered simultaneously. Unlike earlier analyses of these diet problems, here we consider the risk of mortality when foraging and allow risk to differ between habitats. Optimal time allocation strategies and the resultant functional responses are calculated for both one-and two-habitat situations. Mortality risk can substantially change the forager's time allocations and, consequently, its functional responses. Increasing mortality risk in both habitats proportionally can increase use of the habitat that has the greater risk. Time allocation often responds in a non-monotonic fashion to changes in the density of a particular food. As a result, functional responses may decrease with increasing food abundance over one or more ranges of abundance. Experimental findings on the response of grasshopper foraging to the risk of spider predation are compared with the theory. Finally, the possible indirect interactions between the food species in this simple food web are discussed.

F1000Research, Sep 27, 2017

In order to make these reviews as Faculty comprehensive and accessible as possible, peer review t... more In order to make these reviews as Faculty comprehensive and accessible as possible, peer review takes place before publication; the referees are listed below, but their reports are not formally published.

Scavengers

Elsevier eBooks, 2008

Frontiers in Ecology and Evolution, Jul 14, 2017

Prey at risk of predation may experience stress and respond physiologically by altering their met... more Prey at risk of predation may experience stress and respond physiologically by altering their metabolic rates. Theory predicts that such physiological changes should alter prey nutrient demands from N-rich to C-rich macronutrients and shift the balance between maintenance and growth/reproduction. Theory further suggests that for ectotherms temperature stands to exacerbate this stress. But the behavior of many prey species facing perceived predation risk is the opposite of these predictions, consuming more N-rich resources. Here we revisit the original Threshold Elemental Ratio (TER) theoretical framework that inspired the idea of shifts in elemental (C:N) stoichiometry in response to chronic predation stress to reconcile the different prey responses. We examine the interactive effects of predation stress and temperature stress by exploring mathematically how the component physiological variables that determine TER vary individually with temperature. These functional relationships are then embedded into the equation for TER to predict how C and N intake should vary with and without predation stress across temperature gradients. This new theory reconciles the different prey responses and explains why and when species ought to consume more N vs. more C when stressed by perceived predation, depending on the nature of their thermal performance with rising temperature. The theory also points to new ways to conduct experimental evaluations testing the temperature sensitivity of prey to predation stress.

There is a cross-sectoral push amongst conservation practitioners to simultaneously mitigate biod... more There is a cross-sectoral push amongst conservation practitioners to simultaneously mitigate biodiversity loss and climate change, especially as the latter increasingly threatens the former. Growing evidence demonstrates that animals can have substantial impacts on carbon cycling and as such, there are increasing calls to use animal conservation and trophic rewilding to help dually overcome biodiversity loss and climate change. Trophic rewilding is a complex conservation approach to mitigating climate change because it requires accurate baseline estimates of carbon cycling and species impacts on a system, social support for the project, and the actual reintroduction of a species. We join the growing excitement around this potential but caution that rewilding cannot always be justified on carbon benefits alone: a species’ net impact on ecosystem carbon dynamics is context dependent. The need for caution intensifies whenever biodiversity conservation (including rewilding), climate cha...

Spatial subsidies of nutrients within and among ecosystems have profound effects on ecosystem str... more Spatial subsidies of nutrients within and among ecosystems have profound effects on ecosystem structure and functioning. Large animals can be important drivers of nutrient transport as they ingest resources in some habitats and release them in others, even moving nutrients against elevational gradients. In high Andean deserts, vicuñas (Vicugna vicugna) navigate a landscape of fear by migrating daily between productive wet meadows, where there is abundant water and forage but high risk of predation by pumas (Puma concolor), and open plains, where soils are nutrient-poor and forage is less abundant but the risk of predation is low. As they move, vicuñas also defecate and urinate in communal latrines to maintain the cohesion of their family groups. We investigated whether these latrines impacted soil and plant nutrient concentrations across three habitats in the Andean ecosystem (meadows, plains, and high-risk rugged canyons), and used stable isotope analysis to determine the source of...

Plant and Soil, 2019

Aims We tested whether chemical content of individual Tansy plants influences aboveground arthrop... more Aims We tested whether chemical content of individual Tansy plants influences aboveground arthropod and belowground soil microbial community composition. Methods We use Tansy chemical defence composition as focus for our analysis, given that changes in chemical defence are a dominant mechanism expected to modify aboveground and belowground community composition and nutrient cycling. Detailed assessment of arthropod food webs were made on tansy chemotypes. Next generation soil DNA analyses were used to assess soil bacterial community. Results Tansy plants defended by Camphor and Borneol had higher total soil bacterial diversity than control plants (soils under non-Tansy plants) and Tansy chemotypes containing high concentrations of Thujon. Furthermore, the frequency of bacterial genera with a significant role in litter mineralization processes decreased with time in soil associated with Camphor and Borneol chemotypes, indicative of complete microbial decomposition and mineralization of plant material. No such changes occurred in soils associated with Thujon chemotypes. Thujon plants had fewer aphids, ladybirds, spiders, and Orius sp. than other chemotypes. Conclusions Our experiments revealed that Thujon chemotypes had different associated aboveground arthropod and belowground soil microbial communities than Camphor or Borneol chemotypes. The common qualitative response between aboveground and belowground communities to Tansy plant defense is consistent with our hypothesis and extensive literature on plant defense and aboveground and belowground feedbacks.

Journal of Ecology, 2018

Running head: Interaction of nutrients and herbivores on litter decomposition 1. Herbivores often... more Running head: Interaction of nutrients and herbivores on litter decomposition 1. Herbivores often induce changes in plant defensive chemistry or nutrient content that may respectively inhibit or promote microbial decomposition of senesced litter. Often the directional impact of herbivores on decomposition is considered to be a property of a species or ecosystem. While rarely explored, plasticity in the induction of defensive strategies across environmental gradients may also result in divergent impacts of herbivores on decomposition (deceleration vs. acceleration). 2. Here, we examined how soil nutrient conditions determine legacy effects of herbivory, using nine goldenrod genotypes grown across four levels of nutrient supply and with or without grasshopper herbivory. In this species, herbivory induces defensive traits in genotypes grown in high nutrient conditions but induces tolerance (compensatory growth) in low nutrient conditions. We combined senesced litter from each treatment with a common soil inoculum in microcosms and measured soil respiration and litter mass loss over 100 days as estimates of decomposition. 3. Plant genotype, nutrient environment, and herbivory each altered decomposition. The legacy effect of herbivory overwhelmed the positive effect of high soil nutrient supply on

Trends in Ecology & Evolution, 2019

Arguments for the need to conserve aquatic predator (AP) populations often focus on the ecologica... more Arguments for the need to conserve aquatic predator (AP) populations often focus on the ecological and socioeconomic roles they play. Here, we summarize the diverse ecosystem functions and services connected to APs, including regulating food webs, cycling nutrients, engineering habitats, transmitting diseases/parasites, mediating ecological invasions, affecting climate, supporting fisheries, generating tourism, and providing bioinspiration. In some cases, human-driven declines and increases in AP populations have altered these ecosystem functions and services. We present a social ecological framework for supporting adaptive management decisions involving APs in response to social and environmental change. We also identify outstanding questions to guide future research on the ecological functions and ecosystem services of APs in a changing world. Upper-trophic-level predators are ecologically, economically, and culturally important [1-3]. However, many marine and freshwater predators have declined across their range . This has sparked efforts to conserve and manage aquatic species, which have resulted in some population rebounds . Accordingly, we sought to understand the ecological, evolutionary, and socioeconomic roles played by APs and the consequences of their population declines and increases on social and ecological systems. Most reviews describing the ecological roles (see Glossary) of APs have focused on food web dynamics involving marine megafauna . Yet even smaller APs, particularly in freshwater environments, can affect food webs. Growing evidence further suggests that APs are directly and indirectly connected to several other ecosystem functions, including nutrient and carbon cycling , habitat modification , disease transmission , and invasion by exotic species . Moreover, APs are linked to socioecological systems (SESs) that encompass relationships between humans and the environment . Indeed, APs provide diverse ecosystem services, including tourism (e.g., whale watching, shark diving; [20]) and food security [21], as well as the jobs that depend on them. Less obvious is that APs can help mitigate climate change and lead to bioinspired materials and products that benefit human wellbeing . In the sections that follow, we review the ecological roles that APs provide for ecosystem functioning and the attendant ecosystem services they afford to humans (Figure ). We provide examples of ecosystem consequences arising from human-driven declines and increases in AP populations (Table and). We also describe how SESs can be used as a resource APs contribute to various ecosystem functions and services. AP population declines and increases can lead to alterations in these processes. Research priorities remain, including effects of climate change. Application of a social ecological framework can support adaptive management of APs.

Ecology, 2017

Ecological analyses of climate warming explore how rising mean temperature will affect the specie... more Ecological analyses of climate warming explore how rising mean temperature will affect the species composition of communities and their associated functioning. Experimentation usually presumes that warming arises from simultaneous increase in daily maximum (daytime) and minimum (nighttime) temperatures. Yet evidence shows that mean warming arises largely from increasing nighttime temperatures. We report on a 3‐yr experiment that compared the effects of daytime and nighttime warming on a community comprising herbaceous plants, grasshopper herbivores and predatory spiders. We warmed experimental mesocosms 3–4°C above ambient control treatments during the daytime (06:00–18:00 h) or nighttime (18:00–06:00 h). Daytime warming caused spiders to seek a thermal refuge low in the plant canopy and away from grasshopper prey, which allowed grasshoppers to spend more time feeding on a competitively dominant plant species. Nighttime had the opposite effect, where spider activity increased causin...

Ecosphere, 2016

It is predicted that predator‐induced trophic cascades could have important impacts on ecosystem ... more It is predicted that predator‐induced trophic cascades could have important impacts on ecosystem carbon cycling. Yet the magnitude and direction of predator impacts on carbon cycling have not been widely quantified for terrestrial ecosystems. Here, we report on analyses of the potential for gray wolves to have cascading impacts on ecosystem carbon cycling. Our goal is to provide reasonable first approximations of their potential role in this fundamental ecosystem process. We find that gray wolves could lead to an increase in net ecosystem productivity (NEP) of 24.0–52.0 g C·m−2·yr−1 in Isle Royale's boreal forest, and a decrease in NEP of 30.03–102.88 g C·m−2·yr−1 in Yellowstone's grasslands. If such gray wolf impacts scale up to the broader North American boreal and grassland gray wolf range, these estimates suggest a potential for the indirect effects of wolves on yearly carbon fluxes to be on the same order of magnitude as the fossil fuel emissions of 6–20 million passeng...

PloS one, 2016

Human-carnivore conflict is challenging to quantify because it is shaped by both the realities an... more Human-carnivore conflict is challenging to quantify because it is shaped by both the realities and people's perceptions of carnivore threats. Whether perceptions align with realities can have implications for conflict mitigation: misalignments can lead to heightened and indiscriminant persecution of carnivores whereas alignments can offer deeper insights into human-carnivore interactions. We applied a landscape-scale spatial analysis of livestock killed by tigers and leopards in India to model and map observed attack risk, and surveyed owners of livestock killed by tigers and leopards for their rankings of threats across habitats to map perceived attack risk. Observed tiger risk to livestock was greatest near dense forests and at moderate distances from human activity while leopard risk was greatest near open vegetation. People accurately perceived spatial differences between tiger and leopard hunting patterns, expected greater threat in areas with high values of observed risk f...

F1000 - Post-publication peer review of the biomedical literature, 2006

Ecologists have greatly advanced our understanding of the processes that regulate trophic structu... more Ecologists have greatly advanced our understanding of the processes that regulate trophic structure and dynamics in ecosystems. However, the causes of systematic variation among ecosystems remain controversial and poorly elucidated. Contrasts between aquatic and terrestrial ecosystems in particular have inspired much speculation, but only recent empirical quantification. Here, we review evidence for systematic differences in energy flow and biomass partitioning between producers and herbivores, detritus and decomposers, and higher trophic levels. The magnitudes of different trophic pathways vary considerably, with less herbivory, more decomposers and more detrital accumulation on land. Aquaticterrestrial differences are consistent across the global range of primary productivity, indicating that structural contrasts between the two systems are preserved despite large variation in energy input. We argue that variable selective forces drive differences in plant allocation patterns in aquatic and terrestrial environments that propagate upward to shape food webs. The small size and lack of structural tissues in phytoplankton mean that aquatic primary producers achieve faster growth rates and are more nutritious to heterotrophs than their terrestrial counterparts. Plankton food webs are also strongly size-structured, while size and trophic position are less strongly correlated in most terrestrial (and many benthic) habitats. The available data indicate that contrasts between aquatic and terrestrial food webs are driven primarily by the growth rate, size and nutritional quality of autotrophs. Differences in food-web architecture (food chain length, the prevalence of omnivory, specialization or anti-predator defences) may arise as a consequence of systematic variation in the character of the producer community.