Turning up the heat: Temperature influences the relative importance of top‐down and bottom‐up effects

Hoekman, David

doi:10.1890/10-0260.1

Cited by 118 publications

(107 citation statements)

References 30 publications

(36 reference statements)

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“…From field experiments performed in Michigan (non-naive, native range, with a similar temperature range as our experiment), Hoekman (2007Hoekman ( , 2010 found that, although protozoan biovolume greatly decreased in the presence of the mosquito top predator, bacterial density was unaffected. Further, Hoekman (2007) found that the species richness of non-naive prey communities was affected, but only when 20 mosquito larvae were added to the system, which corresponds to high mosquito density in a natural setting (Nastase et al 1995).…”

Section: Discussionsupporting

confidence: 63%

“…When dealing with colonies of protists, the size of a single cell was measured and the species were grouped into one of the three size classes accordingly. Note that we concentrated on species composition because it is already known that W. smithii has a strong effect on the abundance of protists (Addicott 1974;Hoekman 2007Hoekman , 2010Gray et al 2014). Our choice was further motivated by the current interest in the impact of invaders on the diversity and species composition of resident communities (e.g., Hector et al 2002;Fargione and Tilman 2005).…”

Section: Methodsmentioning

confidence: 99%

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Top predators affect the composition of naive protist communities, but only in their early-successional stage

et al. 2015

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from two non-naive and two naive sites, which are climatically similar. We then conducted a common-garden experiment, with and without the presence of the top predator, in which we recorded changes in community composition, body size spectra, bacterial density, and respiration. We found that the top predator had no statistical effect on global measures of community structure and functioning. However, it significantly altered protist composition, but only in naive, early-succession communities, highlighting that the state of community development is important for understanding the impact of invasion.

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Section: Discussionsupporting

confidence: 63%

Section: Methodsmentioning

confidence: 99%

Top predators affect the composition of naive protist communities, but only in their early-successional stage

et al. 2015

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“…For example, in grassland systems Barton and Schmitz (2009) demonstrated that top-down predator effects interact with warming to decrease grasshopper abundance. Additionally, a study on the relative effects of mosquito larvae in a pitcher plant community shows a similar positive relationship between temperature and top-down processes (Hoekman 2010). While this was not quantified in our study, it is possible that warming led to an increase in the top-down predator effects on insect herbivores resulting in lower rates of herbivory in the warmest chambers.…”

Section: Discussionsupporting

confidence: 61%

Interactions in a warmer world: effects of experimental warming, conspecific density, and herbivory on seedling dynamics

et al. 2014

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Abstract. Many effects of a changing climate for organisms, populations, and ecosystems are already apparent. Less studied are the effects of increases in temperature on species interactions. While warming may potentially alter interactions among species, species interactions may also mediate individual species responses to ongoing climatic change. In this experiment we manipulated temperature in field-based, open-top chambers for three years to examine the relationship between biotic interactions and climatic warming on the population dynamics of seedlings of Quercus alba. We investigated the effect of warming on rates of insect herbivory on Q. alba seedlings. Additionally, we assessed the relative effects of increasing temperature, insect herbivory, and conspecific density on seedling survival. We found two unexpected results. First, we observed a negative relationship between temperature and levels of insect herbivory during each year of the experiment. Second, higher levels of herbivory were associated with higher rates of survival to the second year of the study. Although we never detected a direct effect of conspecific density on seedling survival, herbivory and conspecific seedling density did interact to influence Q. alba seedling survival early in the experiment. Taken together, our results indicate species responses to climatic warming may be contingent on intra-and interspecific interactions, sometimes in complicated and counter-intuitive ways.

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“…Our results confirm the well-documented sensitivity of top predators to landscape alteration (Purvis et al 2000;Martinson and Fagan 2014) but suggest that for grassland insect communities, the decline of top predators does not necessarily lead to predator-mediated effects on herbivore communities. However, recent studies have shown that the regulatory effect of top predators on insects can be context dependent as a function of seasonality (Gratton and Denno 2003), wind speed (Barton 2014), and especially temperature (Hoekman 2010;Shurin et al 2012;Barton and Ives 2014). In the current context of global change, caution is therefore required when predicting the relative importance of predatormediated processes versus plant-mediated processes, as it is likely to change as a function of the focal stressors.…”

Section: Discussionmentioning

confidence: 99%

Spatially Heterogeneous Perturbations Homogenize the Regulation of Insect Herbivores

Harvey

MacDougall

2015

The American Naturalist

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Anthropogenic influences on resources and consumers can affect food web regulation, with impacts on trophic structure and ecosystem processes. Identifying how these impacts unfold is challenging because alterations to one or both resources and consumers can similarly transform community structure, especially for intermediate consumers. To date, empirical testing of perturbations on trophic regulation has been limited by the difficulty in separating the direct effect of perturbations on species composition and diversity versus those unfolding indirectly via altered feeding pathways. Moreover, disentangling the independent and interactive impacts of co-varying stressors that characterize human-altered systems has been an ongoing analytical challenge. We used a large-scale meta-community experiment in grasslands to test how resource inputs, stand perturbation, and spatial factors affect regulation of insect herbivores in tri-trophic grassland food webs. Using path-model comparisons, we observed significant simplification of food web regulation on insect herbivores, shifting from mixed predator-resource regulation in unaltered mainland areas, to strictly resource-based regulation with landscape perturbation and fragmentation. Most changes were attributed to homogenization of plant community caused by landscape fragmentation and the deterministic influence of eutrophication that reduced among-patch beta-diversity. This led to a simplified food web dominated by fewer, but more abundant herbivore taxa. Our work implies that anthropogenic perturbation relating to resources and spatial isolation can transform the regulation of food web diversity, structure and function. abstract: Anthropogenic influences on resources and consumers can affect food web regulation, with impacts on trophic structure and ecosystem processes. Identifying how these impacts unfold is challenging because alterations to one or both resources and consumers can similarly transform community structure, especially for intermediate consumers. To date, empirical testing of perturbations on trophic regulation has been limited by the difficulty in separating the direct effect of perturbations on species composition and diversity from those unfolding indirectly via altered feeding pathways. Moreover, disentangling the independent and interactive impacts of covarying stressors that characterize human-altered systems has been an ongoing analytical challenge. We used a large-scale metacommunity experiment in grasslands to test how resource inputs, stand perturbation, and spatial factors affect regulation of insect herbivores in tritrophic grassland food webs. Using path-model comparisons, we observed significant simplification of food web regulation on insect herbivores, shifting from mixed predator-resource regulation in unaltered mainland areas to strictly resource-based regulation with landscape perturbation and fragmentation. Most changes were attributed to homogenization of plant community caused by landscape fragmentation and the deterministic...

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Turning up the heat: Temperature influences the relative importance of top‐down and bottom‐up effects

Cited by 118 publications

References 30 publications

Top predators affect the composition of naive protist communities, but only in their early-successional stage

Top predators affect the composition of naive protist communities, but only in their early-successional stage

Interactions in a warmer world: effects of experimental warming, conspecific density, and herbivory on seedling dynamics

Spatially Heterogeneous Perturbations Homogenize the Regulation of Insect Herbivores

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