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Parameter estimates and confidence limits for classic and size-dependent Type II functional response model fits for water bug and dragonfly predators foraging on red-eyed tree- frog tadpoles
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The functional response is a critical link between consumer and resource dynamics, describing how a consumer's feeding rate varies with prey density. Functional response models often assume homogenous prey size and size-independent feeding rates. However, variation in prey size due to ontogeny and competition is ubiquitous, and predation rates are...
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Assessment risk and limited behavioral plasticity in tadpoles of Rhinella ornata (Anura, Bufonidae). Anuran tadpoles are important elements of trophic networks in aquatic environments, being food resource for many types of predators. Thus, the tadpoles exhibit a great variety of defense mechanisms that may be morphological, behavioral and/or physio...
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... Second, simultaneous fitting generates more accurate and precise parameter estimates than fitting conditions independently (Uszko et al., 2020). Response surfaces have successfully been used to investigate the effect of prey body size (McCoy et al., 2011;McCoy & Bolker, 2008) and temperature (Gilioli et al., 2005;Uszko et al., 2020) on predator's functional response. Our study is the first to use this design to investigate TIMs and highlights the potential of response surfaces to understand species interactions and predict community dynamics. ...
Trophic interaction modifications (TIM) are widespread in natural systems and occur when a third species indirectly alters the strength of a trophic interaction. Past studies have focused on documenting the existence and magnitude of TIMs; however, the underlying processes and long‐term consequences remain elusive. To address this gap, we experimentally quantified the density‐dependent effect of a third species on a predator's functional response. We conducted short‐term experiments with ciliate communities composed of a predator, prey and non‐consumable ‘modifier’ species. In both communities, increasing modifier density weakened the trophic interaction strength, due to a negative effect on the predator's space clearance rate. Simulated long‐term dynamics indicate quantitative differences between models that account for TIMs or include only pairwise interactions. Our study demonstrates that TIMs are important to understand and predict community dynamics and highlights the need to move beyond focal species pairs to understand the consequences of species interactions in communities.
... , and salinity (Allen et al., 2017;Haramura, 2016) can trigger early hatching. Embryos that can initiate hatching in response to environmental cues may face tradeoffs; while early hatching allows embryos to escape predation, hatchlings may be smaller or less developed (Delia et al., 2019;Poo et al., 2023), which can be associated with greater larval predation risk and lower larval survival (Delia et al., 2019;Gomez-Mestra et al., 2008;McCoy et al., 2011; but see Vonesh & Bolker, 2005). ...
Hatching plasticity allows animals to initiate hatching in response to environmental
cues including predation, flooding, and hypoxia. In species with terrestrial eggs but
aquatic larvae, hatching plasticity often manifests as extended development of em-
bryos when water is not available. Although these effects are taxonomically wide-
spread, little attention has focused on differences in plasticity across closely related
species with terrestrial and aquatic embryos. We propose that the terrestrial embry-
onic environment favors slower and prolonged development and, consequently, that
we should see differences in development between closely related species that differ
in where they lay their eggs. We test this hypothesis by comparing embryonic devel-
opment between two mole salamanders, Ambystoma opacum and A. annulatum. Most
Ambystoma lay eggs submerged in ponds but A. opacum lays its eggs on land, where
hatching is triggered when eggs are submerged by rising pond levels. Embryos of both
species were reared under common laboratory conditions simulating both aquatic
and terrestrial nest sites. Consistent with our hypothesis, we found that A. opacum
embryos exhibited slower development and took longer to hatch than A. annulatum
embryos in both rearing environments. Furthermore, we observed in A. opacum a
plasticity in hatching stage that was absent in A. annulatum. Our results indicate that
the terrestrial- laying A. opacum has evolved slower and prolonged development rela-
tive to its aquatic-laying congener and suggest that embryonic survival in the unpre-
dictable terrestrial environment may be facilitated by developmental plasticity.
... We measured the temperature-dependent functional response of Pantala spp. on Ae. atropalpus using five constant temperature treatments (20, 24, 28, 32, and 36°C) and five starting prey density treatments (20, 40, 60, 80, and 120 larvae). A response surface design was employed to reduce the number of treatment combinations required to estimate the functional response (Appendix S1: Figure S1; McCoy et al. 2011;Davidson et al. 2021a). This resulted in 13 treatment combinations with between 6-8 ...
Warming has broad and often nonlinear impacts on organismal physiology and traits, allowing it to impact species interactions like predation through a variety of pathways that may be difficult to predict. Predictions are commonly based on short‐term experiments and models, and these studies often yield conflicting results depending on the environmental context, spatiotemporal scale, and the predator and prey species considered. Thus, the accuracy of predicted changes in interaction strength, and their importance to the broader ecosystems they take place in, remain unclear. Here, we attempted to link one such set of predictions generated using theory, modeling, and controlled experiments to patterns in the natural abundance of prey across a broad thermal gradient. To do so, we first predicted how warming would impact a stage‐structured predator–prey interaction in riverine rock pools between Pantala spp. dragonfly nymph predators and Aedes atropalpus mosquito larval prey. We then described temperature variation across a set of hundreds of riverine rock pools (n = 775) and leveraged this natural gradient to look for evidence for or against our model's predictions. Our model's predictions suggested that warming should weaken predator control of mosquito larval prey by accelerating their development and shrinking the window of time during which aquatic dragonfly nymphs could consume them. This was consistent with data collected in rock pool ecosystems, where the negative effects of dragonfly nymph predators on mosquito larval abundance were weaker in warmer pools. Our findings provide additional evidence to substantiate our model‐derived predictions while emphasizing the importance of assessing similar predictions using natural gradients of temperature whenever possible.
... Here, we explore when prey are stage structured with a juvenile stage vulnerable to predation and an adult stage that is invulnerable to predation. Many species experience ontogenetic shifts over their lifetime, and their vulnerabilities to certain predators shift in tandem (Werner and Gilliam 1984;Davidson et al. 2021;McCoy et al. 2011). Commonly, prey may start as small and vulnerable to predation and then grow and shift to large and invulnerable, in what has been referred to as a "size refuge" (Werner and Gilliam 1984). ...
Climate warming directly influences the developmental and feeding rates of organisms. Changes in these rates are likely to have consequences for species interactions, particularly for organisms affected by stage- or size-dependent predation. However, because of differences in species-specific responses to warming, predicting the impact of warming on predator and prey densities can be difficult. We present a general model of stage-dependent predation with temperature-dependent vital rates to explore the effects of warming when predator and prey have different thermal optima. We found that warming generally favored the interactor with the higher thermal optimum. Part of this effect occurred due to the stage-dependent nature of the interaction and part due to thermal asymmetries. Interestingly, below the predator and prey thermal optima, warming caused prey densities to decline, even as increasing temperature improved prey performance. We also parameterize our model using values from a well-studied system, Arctia virginalis and Formica lasioides, in which the predator has a warmer optimum. Overall, our results provide a general framework for understanding stage- and temperature-dependent predator–prey interactions and illustrate that the thermal niche of both predator and prey is important to consider when predicting the effects of climate warming.
... The functional response describes instantaneous mortality rates (Holling 1959a(Holling , b, 1965Soluk 1993;Vonesh and Bolker 2005;McCoy et al. 2011), but when paired with other processes, short-term mortality can be linked to longer-term consumer and resource population dynamics Oaten and Murdoch 1975;Hassell 1978;Murdoch et al. 2003). In basic Lotka-Volterra consumer-resource models (Lotka 1910;Volterra 1926;Berryman 1992), the functional response, consumer background mortality, consumer conversion efficiency (i.e., via the numerical response, the change in consumer abundance as a function of change in resource abundance), and the resource rate of increase and carrying capacity provide the framework for predicting changes in consumer and resource abundance through time. ...
The Comparative Functional Response Approach (CFRA) was developed to provide a practical methodology by which short-term experiments can be used to forecast the longer-term impacts of a potential invading consumer. The CFRA makes inferences about potential invader impact based on comparisons of the functional responses of invader and native consumers on native resources in a common experimental venue. Application of the CFRA and derivative approaches have proliferated since it was introduced in 2014. Here we examine the conceptual foundations of the CFRA within the context of basic Lotka–Volterra consumer-resource theory. Our goals are to assess whether core predictions of the CFRA hold within this framework, to consider the relative importance of background mortality and consumer assimilation efficiency in determining predator impact, and to leverage this conceptual framework to expand the discussion regarding stability and long term consumer and resource dynamics. The CFRA assertion that consumers with a higher functional response will have larger impacts on resources only holds as long as all other parameters are equal, but basic theory indicates that predator impacts on prey abundance and stability will depend more on variation in conversion efficiency and background mortality. While examination of the CFRA within this framework highlights limitations about its current application, it also points to potential strengths that are only revealed when a theoretical context is identified, in this case the implications for stability and conceptual links to competition theory.
... Many species, including insects, undergo ontogenetic shifts, either in the form of habitats or life cycles with distinct developmental stages [20]. This is critical, since the consumption of some prey species is dependent on the prey body size or its developmental stage [26]. Predator and prey traits may sometimes have asymmetric thermal responses; for instance, the optimal temperatures for foraging and development are different, or predator and prey traits respond differentially across a thermal gradient [20]. ...
The tea green leaf hopper, Empoasca onukii Matsuda, is a severe pest of tea plants. Volatile emissions from tea shoots infested by the tea green leafhopper may directly repel insect feeding or attract natural enemies. Many studies have been conducted on various aspects of the tritrophic relationship involving tea plants, tea green leafhoppers and natural enemies. However, mathematic models which could explain the dynamic mechanisms of this tritrophic interaction are still lacking. In the current work, we constructed a realistic and stochastic model with temperature-dependent features to characterize the tritrophic interactions in the tea agroecosystem. Model outputs showed that two leafhopper outbreaks occur in a year, with their features being consistent with field observations. Simulations showed that daily average effective accumulated temperature (EAT) might be an important metric for outbreak prediction. We also showed that application of slow-releasing semiochemicals, as either repellents or attractants, may be highly efficacious for pest biocontrol and can significantly increase tea yields. Furthermore, the start date of applying semiochemicals can be optimized to effectively increase tea yields. The current model qualitatively characterizes key features of the tritrophic interactions and provides critical insight into pest control in tea ecosystems.
... Functional responses often are estimated without regard to body size or other traits (Jalali et al., 2010;. However, variation in prey size owing to ontogeny and individual variation is ubiquitous, and predation rates typically depend on the size of the predator, the prey, or both (Cogni et al., 2002;Mccoy et al., 2011). This variation stems from the effect of predator and prey body size on the functional response parameters (i.e., handling time and space clearance rate) (DeLong, 2014;Uiterwaal and DeLong, 2020;Buba et al., 2021). ...
Functional responses are central to predator–prey dynamics and describe how predation varies with prey abundance. Functional responses often are measured without regard to prey size (i.e., body mass) or the temperature dependence of feeding rates. However, variation in prey size within populations is ubiquitous, and predation rates are often both size and temperature-dependent. Here, we assessed functional responses of larvae and adult Harmonia axyridis on the 1st, 2nd, and 3rd instars of the prey Spodoptera litura across a range of temperatures (i.e., 15, 20, 25, 30, and 35°C). The type and parameters of the functional responses were determined using logistic regression and fitted to the Roger's random predator equation. The magnitude of predation varied with the predator and prey stage, but prey predation increased with warming and predator age. Predation by the female and 4th instar of H. axyridis on the 1st instar of prey was greater, followed by the 2nd and 3rd instar of prey S. litura. No predation occurred on the larger prey for the 1st, 2nd, and 3rd instars of H. axyridis. The larvae and adult H. axyridis produced a type II (hyperbolic) functional response curve across all temperatures and the three prey types they consumed. Space clearance rates, handling time, and maximum predation rates of H. axyridis changed with temperature and prey size, increasing with temperature and decreasing with prey size, suggesting more predation will occur on younger prey. This study indicates an interactive role of temperature and prey/predator size in shaping functional responses, which might complicate the planning of effective biocontrol strategies against this serious pest.
... The function innovatively takes into consideration the efficacy and speed of behaviour change. It models the infection growth in the presence of behaviour change and the model fits better to EVD data from the two countries considered; see also [36]. The effective transmission rate of EVD is represented by the parameter β and the efficacy of behaviour change is represented by a parameter p ðp ∈ ½0, 1Þ such that p = 0 corresponds to an uncontrolled behaviour that fuels EVD spread and p = 1 corresponds to a perfectly controlled behaviour that stops EVD spread. ...
The role of human behaviour in the dynamics of infectious diseases cannot be underestimated. A clear understanding of how human behaviour influences the spread of infectious diseases is critical in establishing and designing control measures. To study the role that human behaviour plays in Ebola disease dynamics, in this paper, we design an Ebola virus disease model with disease transmission dynamics based on a new exponential nonlinear incidence function. This new incidence function that captures the reduction in disease transmission due to human behaviour innovatively considers the efficacy and the speed of behaviour change. The model’s steady states are determined and suitable Lyapunov functions are built. The proofs of the global stability of equilibrium points are presented. To demonstrate the utility of the model, we fit the model to Ebola virus disease data from Liberia and Sierra Leone. The results which are comparable to existing findings from the outbreak of 2014 − 2016 show a better fit when the efficacy and the speed of behaviour change are higher. A rapid and efficacious behaviour change as a control measure to rapidly control an Ebola virus disease epidemic is advocated. Consequently, this model has implications for the management and control of future Ebola virus disease outbreaks.
... The attack coefficient has been suggested to exhibit a humpshaped relationship with predator-prey body mass ratio McCoy et al., 2011;Rall et al., 2011), underpinned by increasing attack coefficients for larger predators and weaker or no effects of prey size (Rall et al., 2012;Uiterwaal and DeLong, 2020). In contrast, handling time has a U-shaped relationship with predator-prey body mass ratio (Rall et al., 2012), underpinned by decreasing handling time for larger predators and smaller prey Kalinkat et al., 2011). ...
... Our findings also provide strong support for a hump-shaped relationship between attack coefficient and predator-prey body mass ratio, which has been widely reported in the literature McCoy et al., 2011;Rall et al., 2011). This indicates that C. boltonii has an optimum prey size that can be successfully attacked, and they may not perceive prey that are > 1,000 times smaller, or struggle to subdue prey that are < 10 times smaller than themselves (Supplementary Figures 3A-C). ...
Environmental temperature and body size are two prominent drivers of predation. Despite the ample evidence of their independent effects, the combined impact of temperature and predator-prey body size ratio on the strength and stability of trophic interactions is not fully understood. We experimentally tested how water temperature alters the functional response and population stability of dragonfly nymphs (Cordulegaster boltonii) feeding on freshwater amphipods (Gammarus pulex) across a gradient of their body size ratios. Attack coefficients were highest for small predators feeding on small prey at low temperatures, but shifted toward the largest predators feeding on larger prey in warmer environments. Handling time appeared to decrease with increasing predator and prey body size in the cold environment, but increase at higher temperatures. These findings indicate interactive effects of temperature and body size on functional responses. There was also a negative effect of warming on the stability of predator and prey populations, but this was counteracted by a larger predator-prey body size ratio at higher temperatures. Here, a greater Hill exponent reduced feeding at low prey densities when predators were much larger than their prey, enhancing the persistence of both predator and prey populations in the warmer environment. These experimental findings provide new mechanistic insights into the destabilizing effect of warming on trophic interactions and the key role of predator-prey body size ratios in mitigating these effects.
... We examined how the body masses of predators and prey constrain their interaction strengths. Corroborating prior functional-response studies (Wahlstr€ om et al. 2000;Aljetlawi et al. 2004;Vonesh & Bolker 2005;Vucic-Pestic et al. 2010b;McCoy et al. 2011;, we found power-law relationships between handling time and predator as well as prey mass and hump-shaped relationships between capture rates and predator-prey body-mass ratios. In addition, our study demonstrates for the first time a systematic bodymass dependency of the capture exponent, converting hyperbolic (type-II) into sigmoid (type-III) functional responses with increasing predator body mass and decreasing prey body mass. ...
... A prior model improvement included an allometric scaling relationship of carrying capacities and more realistic scaling relationships of capture rates (Weitz & Levin 2006). In recent years, hump-shaped scaling of capture rates with predator-prey body-mass ratios became widely accepted (Wahlstr€ om et al. 2000;Aljetlawi et al. 2004;Vonesh & Bolker 2005;Vucic-Pestic et al. 2010b;McCoy et al. 2011;. Altogether, these efforts helped to eliminate biologically unrealistic trait combinations (Brose 2010) and implementations of these improved allometric constraints into the bioenergetic model were successfully employed to predict population dynamics in complex multi-predator communities Schneider et al. 2012). ...
In this thesis, a collection of studies is presented that advance research on complex food webs in several directions. Food webs, as the networks of predator-prey interactions in ecosystems, are responsible for distributing the resources every organism needs to stay alive. They are thus central to our understanding of the mechanisms that support biodiversity, which in the face of increasing severity of anthropogenic global change and accelerated species loss is of highest importance, not least for our own well-being. The studies in the first part of the thesis are concerned with general mechanisms that determine the structure and stability of food webs. It is shown how the allometric scaling of metabolic rates with the species' body masses supports their persistence in size-structured food webs (where predators are larger than their prey), and how this interacts with the adaptive adjustment of foraging efforts by consumer species to create stable food webs with a large number of coexisting species. The importance of the master trait body mass for structuring communities is further exemplified by demonstrating that the specific way the body masses of species engaging in empirically documented predator-prey interactions affect the predator's feeding rate dampens population oscillations, thereby helping both species to survive. In the first part of the thesis it is also shown that in order to understand certain phenomena of population dynamics, it may be necessary to not only take the interactions of a focal species with other species into account, but to also consider the internal structure of the population. This can refer for example to different abundances of age cohorts or developmental stages, or the way individuals of different age or stage interact with other species. Building on these general insights, the second part of the thesis is devoted to exploring the consequences of anthropogenic global change on the persistence of species. It is first shown that warming decreases diversity in size-structured food webs. This is due to starvation of large predators on higher trophic levels, which suffer from a mismatch between their respiration and ingestion rates when temperature increases. In host-parasitoid networks, which are not size-structured, warming does not have these negative effects, but eutrophication destabilises the systems by inducing detrimental population oscillations. In further studies, the effect of habitat change is addressed. On the level of individual patches, increasing isolation of habitat patches has a similar effect as warming, as it leads to decreasing diversity due to the extinction of predators on higher trophic levels. In this case it is caused by dispersal mortality of smaller and therefore less mobile species on lower trophic levels, meaning that an increasing fraction of their biomass production is lost to the inhospitable matrix surrounding the habitat patches as they become more isolated. It is further shown that increasing habitat isolation desynchronises population oscillations between the patches, which in itself helps species to persist by dampening fluctuations on the landscape level. However, this is counteracted by an increasing strength of local population oscillations fuelled by an indirect effect of dispersal mortality on the feeding interactions. Last, a study is presented that introduces a novel mechanism for supporting diversity in metacommunities. It builds on the self-organised formation of spatial biomass patterns in the landscape, which leads to the emergence of spatio-temporally varying selection pressures that keep local communities permanently out of equilibrium and force them to continuously adapt. Because this mechanism relies on the spatial extension of the metacommunity, it is also sensitive to habitat change. In the third part of the thesis, the consequences of biodiversity for the functioning of ecosystems are explored. The studies focus on standing stock biomass, biomass production, and trophic transfer efficiency as ecosystem functions. It is first shown that increasing the diversity of animal communities increases the total rate of intra-guild predation. However, the total biomass stock of the animal communities increases nevertheless, which also increases their exploitative pressure on the underlying plant communities. Despite this, the plant communities can maintain their standing stock biomass due to a shift of the body size spectra of both animal and plant communities towards larger species with a lower specific respiration rate. In another study it is further demonstrated that the generally positive relationship between diversity and the above mentioned ecosystem functions becomes steeper when not only the feeding interactions but also the numerous non-trophic interactions (like predator interference or competition for space) between the species of an ecosystem are taken into account. Finally, two studies are presented that demonstrate the power of functional diversity as explanatory variable. It is interpreted as the range spanned by functional traits of the species that determine their interactions. This approach allows to mechanistically understand how the ecosystem functioning of food webs with multiple trophic levels is affected by all parts of the food web and why a high functional diversity is required for efficient transportation of energy from primary producers to the top predators. The general discussion draws some synthesising conclusions, e.g. on the predictive power of ecosystem functioning to explain diversity, and provides an outlook on future research directions.