Jennifer Adams Krumins

Population and community resilience in multitrophic communities.

Diversity-stability relationships have long been a topic of controversy in ecology, but one whose importance has been re-highlighted by increasing large-scale threats to global biodiversity. The ability of a community to recover from a perturbation (or resilience) is a common measure of stability that has received a large amount of theoretical attention. Yet, general expectations regarding diversity-resilience relations remain elusive. Moreover, the effects of productivity and its interaction with diversity on resilience are equally unclear. We examined the effects of species diversity, species composition, and productivity on population-and community-level resilience in experimental aquatic food webs composed of bacteria, algae, heterotrophic protozoa, and rotifers. Productivity manipulations were crossed with manipulations of the number of species and species compositions within trophic groups. Resilience was measured by perturbing communities with a nonselective, density-independent, mortality event and comparing responses over time between perturbed communities and controls. We found evidence that species diversity can enhance resilience at the community level (i.e., total community biomass), though this effect was more strongly expressed in low-productivity treatments. Diversity effects on resilience were driven by a sampling/selection effect, with resilient communities showing rapid response and dominance by a minority of species (primarily unicellular algae). In contrast, diversity had no effect on mean population-level resilience. Instead, the ability of a communitys populations to recover from perturbations was dependent on species composition. We found no evidence of an effect of productivity, either positive or negative, on community- or population-level resilience. Our results indicate that the role of diversity as an insurer of stability may depend on the level of biological organization at which stability is measured, with effects emerging only when focusing on aggregate community properties.

Plant–soil feedbacks of exotic plant species across life forms: a meta-analysis

Invasive exotic plant species effects on soil biota and processes in their new range can promote or counteract invasions via changed plant–soil feedback interactions to themselves or to native plant species. Recent meta-analyses reveale that soil influenced by native and exotic plant species is affecting growth and performance of natives more strongly than exotics. However, the question is how uniform these responses are across contrasting life forms. Here, we test the hypothesis that life form matters for effects on soil and plant–soil feedback. In a meta-analysis we show that exotics enhanced C cycling, numbers of meso-invertebrates and nematodes, while having variable effects on other soil biota and processes. Plant effects on soil biota and processes were not dependent on life form, but patterns in feedback effects of natives and exotics were dependent on life form. Native grasses and forbs caused changes in soil that subsequently negatively affected their biomass, whereas native trees caused changes in soil that subsequently positively affected their biomass. Most exotics had neutral feedback effects, although exotic forbs had positive feedback effects. Effects of exotics on natives differed among plant life forms. Native trees were inhibited in soils conditioned by exotics, whereas native grasses were positively influenced in soil conditioned by exotics. We conclude that plant life form matters when comparing plant–soil feedback effects both within and between natives and exotics. We propose that impact analyses of exotic plant species on the performance of native plant species can be improved by comparing responses within plant life form.

Soil and Freshwater and Marine Sediment Food Webs: Their Structure and Function

The food webs of terrestrial soils and of freshwater and marine sediments depend on adjacent aboveground or pelagic ecosystems for organic matter input that provides nutrients and energy. There are important similarities in the flow of organic matter through these food webs and how this flow feeds back to primary production. In both soils and sediments, trophic interactions occur in a cycle in which consumers stimulate nutrient cycling such that mineralized resources are made available to the primary producers. However, aquatic sediments and terrestrial soils differ greatly in the connectivity between the production and the consumption of organic matter. Terrestrial soils and shallow aquatic sediments can receive organic matter within hours of photosynthesis when roots leak carbon, whereas deep oceanic sediments receive organic matter possibly months after carbon assimilation by phytoplankton. This comparison has implications for the capacity of soils and sediments to affect the global carbon balance.

Interactions in soil: promoting plant growth.

Over the past decade, there has been a rapidly expanding scientific literature focused on linking concepts of population, community and community ecology, and this is fast becoming one of the most active branches of ecology. Understanding these linkages also has considerable relevance to understanding conservation biology, causes and consequences of biodiversity, and the delivery of ecosystem services. This series aims to publish novel syntheses offering new insights into linkages among these topics. The scope is deliberately broad, and examples of topics that are of interest include (but are in no way restricted to): Biotic interactions; Ecosystem dynamics, Stability and resilience; Aboveground-belowground interactions; Relationships between biodiversity and ecosystem processes; Ecology of global environmental change; Biological invasions; Ecological restoration. All ecosystem types (including terrestrial and aquatic) and groups of organisms are of interest, as are syntheses on both fundamental and applied science.

Herbivory and Stoichiometric Feedbacks to Primary Production

Established theory addresses the idea that herbivory can have positive feedbacks on nutrient flow to plants. Positive feedbacks likely emerge from a greater availability of organic carbon that primes the soil by supporting nutrient turnover through consumer and especially microbially-mediated metabolism in the detrital pool. We developed an entirely novel stoichiometric model that demonstrates the mechanism of a positive feedback. In particular, we show that sloppy or partial feeding by herbivores increases detrital carbon and nitrogen allowing for greater nitrogen mineralization and nutritive feedback to plants. The model consists of differential equations coupling flows among pools of: plants, herbivores, detrital carbon and nitrogen, and inorganic nitrogen. We test the effects of different levels of herbivore grazing completion and of the stoichiometric quality (carbon to nitrogen ratio, C:N) of the host plant. Our model analyses show that partial feeding and plant C:N interact because when herbivores are sloppy and plant biomass is diverted to the detrital pool, more mineral nitrogen is available to plants because of the stoichiometric difference between the organisms in the detrital pool and the herbivore. This model helps to identify how herbivory may feedback positively on primary production, and it mechanistically connects direct and indirect feedbacks from soil to plant production.

Emergent multiple predator effects in an experimental microbial community

Studies on multiple predator effects have typically focused on metazoans. Here we examined the effects of multiple consumers on bacteria. Specifically, we investigated the separate and combined effects of two common bacterivorous ciliates, Colpidium striatum and Paramecium caudatum, on a simple bacterial assemblage. Non-additive multiple predator effects emerged for all bacterial species significantly affected by grazing, where bacterial responses in the two-consumer treatment cannot be predicted by summing the separate effects of the two consumers. Some species showed risk reduction (observed responses less than expected), whereas others showed risk enhancement (observed responses larger than expected). We attributed risk alteration to the interference between the two consumers. Contradictory to theoretical predictions, total bacterial abundance in the two-consumer treatment did not differ from single-consumer treatments and consumer-free controls, due largely to risk reduction and compensatory responses within the bacterial assemblage. Decomposition of particulate organic matter was greater in the two-consumer treatment than the Paramecium single-consumer treatment, but did not differ among other treatments. These results suggest that the presence of multiple consumers may have unexpected impacts on the structure and functioning of bacterial communities.

The Positive Effects of Trophic Interactions in Soil

The feedbacks between plants and their soil communities determine primary production and moderates the ecosystem services they both provide. Feedbacks can be perceived as positive or negative, but historically, the greatest attention has be given to the role of negative feedbacks in shaping plant production and community development. Although we understand the role of mycorrhizae and bacterial symbionts fairly well, fewer studies have addressed the role of positive feedbacks and facilitation associated with trophic interactions and food web activity. Due to the close spatial scale of rhizosphere food webs, they function more like a cycle than a linear food chain. This results in consumer mediated nutrient cycling that frequently feeds back positively on plant production even when considering herbivory as an isolated process. Herbivores enrich the environment by increasing organic matter and high quality mineral nutrients to the soil. A process mediated by the stoichiometric imbalance between consumers and resources. Likewise, the functional and taxonomic biodiversity of food webs in soils will understandably affect the degree of positive feedbacks to plant production. This is important to consider in an increasingly human dominated world. It is possible that community composition and functioning in disturbed environments is driven to a greater degree by positive rather than negative feedbacks. In this environment, soils will play an essential role in maintaining ecosystem health.

Plant Productivity, Ectomycorrhizae, and Metal Contamination in Urban Brownfield Soils

Abstract The soil contamination legacy of postindustrial sites has become an issue of increasing ecological and public health concern. This study examines the ectomycorrhizal and above-ground plant relationships in the metaliferous soil of an urban brownfield. Ectomycorrhizal fungi (EMF) were microscopically identified by physical morphotyping followed by sequencing of ribosomal DNA. Plant productivity was assessed through Leaf Area Index (LAI) measurements taken from May through July 2012 and 2013. Results indicate that there were significant changes in EMF community composition and plant productivity based on their position along a total soil metal load gradient. Cenococcum geophilum was the dominant species in the soils where total soil metal load was below previously established threshold values, and Russula species were the dominant genera in soils where the total soil metal load was above the threshold value. Higher LAI values are seen in environments with higher soil metal levels. However, higher LAI could be due to multiple factors such as increased moisture and the dominance of metal-tolerant tree species. This study suggests that soil metal contamination affects plant productivity and EMF community composition and supports the idea that EMF species have varying levels of tolerance for metals.

No Paradox for Invasive Plants

The Perspective “An invasive plant paradox” by M. E. Rout and R. M. Callaway (8 May, p. [734][1]) overgeneralizes the effect of invasive plants on the nitrogen cycle. An invasive plants impact on nitrogen cycling is based on plant identity rather than origin. Invasive nitrogen-fixing plants can

Root Growth Responses to Soil Amendment in an Urban Brownfield

Ecological Restoration Vol. 33, No. 1, 2015 ISSN 1522-4740 E-ISSN 1543-4079 ©2015 by the Board of Regents of the University of Wisconsin System. Root Growth Responses to Soil Amendment in an Urban Brownfield Frank J. Gallagher (Department of Landscape Architecture, Rutgers, The State University of New Jersey, New Brunswick, NJ), Joshua S. Caplan (corresponding author: Department of Ecology, Evolution & Natural Resources, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, jcaplan@aesop.rutgers.edu), Jennifer Adams Krumins (Department of Biology and Molecular Biology, Montclair State University, Montclair, NJ) and Jason C. Grabosky (Department of Ecology, Evolution & Natural Resources, Rutgers, The State University of New Jersey, New Brunswick, NJ).