Loralee Larios

Competition and soil resource environment alter plant-soil feedbacks for native and exotic grasses.

Our understanding of how feedbacks between plants and soil microbial communities may contribute to plant invasions and exotic dominance is limited by our understanding of how feedbacks may shift in the light of other ecological processes. In a greenhouse experiment, we found that the strength of plant–soil feedbacks shifted for both a native and exotic as soil microbial communities changed along a gradient of soil nitrogen (N) availability. Moreover, competition from an exotic grass minimized the beneficial feedback between the native grass and its soil microbial community when the soil community was from a high N environment.

Seed Supply, Recruitment, and Assembly: Quantifying Relative Seed and Establishment Limitation in a Plant Community Context

There is a growing consensus that the relative constraints of seed limitation and establishment limitation in recruitment strongly influence abundance patterns in plant communities. Although these constraints have direct relevance to coexistence, most investigations utilize a seed addition approach that offers limited insight into these dynamics. Here we report the results of an assembly experiment with annual plant species from California grasslands to examine how propagule pool characteristics (dominant species abundance, functional diversity) influence establishment and seed limitation (density independence and density dependence across a gradient of seed supply) for each species, as well as how these constraints affect community diversity. Species were predominantly colimited by seed and establishment constraints, exhibiting saturating recruitment functions with increased seed supply. Consistent with competition-colonization trade-off predictions, recruitment constraints often depended on the degree of seed limitation of the competitive dominant, Brassica nigra; diversity was greatest in communities where Brassica was seed limited. Functional similarity within the propagule pool did not affect recruitment across a range of seed supply; likewise, functional diversity of the propagule pool was not related to community diversity. We conclude that seed limitation of the dominant species rather than niche similarity influences interspecific competition for safe sites and scales up to affect community-level diversity.

Incorporating the effects of generalist seed predators into plant community theory

Post-dispersal seed predators contribute substantially to seed loss across many ecosystems. Most research has focused on understanding sources of variation in seed loss, without appreciating the implications of seed predation for plant coexistence, community assembly and broader community theory. Meanwhile, research aimed at understanding coexistence and community assembly processes in plant communities has focused on axes of dispersal and resource competition and the traits influencing these processes, without accounting for the role of generalist seed predators. We review the unique features of post-dispersal seed predation and assess the implications of seed loss on three critical components of plant community organization˗ coexistence, community structure and plant invasions ˗ pointing to both important gaps in theory and empirical knowledge. We highlight how understanding fundamental controls on plant recruitment is central to determining how seed predation affects plant recruitment and coexistence. We discuss how accounting for seed predator foraging strategies may shift trait-based inferences of community assembly. Synthesis. We argue that seed predation by generalist consumers, which is pervasive in temperate communities, should be better incorporated into plant community theory. Experiments that specifically incorporate the presence and attributes of the seed predator community and that follow seed fate would fill important knowledge gaps. Particularly needed are studies focused on strengthening the connections between seed removal and plant establishment and linking selective and density dependent foraging strategies to plant traits. Advancing our understanding of the processes regulating plant coexistence and community assembly requires that future research not only acknowledge but incorporate generalist consumers’ effects on plant communities. This article is protected by copyright. All rights reserved.

Where and how to restore in a changing world: a demographic-based assessment of resilience

Summary Managers are increasingly looking to apply concepts of resilience to better anticipate and understand conservation and restoration in a changing environment. In this study, we explore how information on demography (recruitment, growth and survival) and competitive effects in different environments and with different starting species abundances can be used to better understand resilience. We use observational and experimental data to better understand dynamics between native Stipa pulchra and exotic Avena barbata and fatua, grasses characteristic of native and invaded grasslands in California, at three different levels of nitrogen (N) representative of a range of pollution via atmospheric deposition. A modelling framework that incorporates this information on demography and competition allows us to forecast dynamics over time. Our results showed that resilience of native grasslands depends on N inputs, where natural recovery should be possible at low N levels whereas native persistence would be difficult at high N levels. Hysteresis was evident at moderate N levels, where the starting conditions mattered. Synthesis and applications. The resilience of both invaded and native grasslands is influenced by nitrogen inputs. Our modelling approach gives direction about how best to allocate limited management resources as baselines shift: where natural recovery is possible, where best to allocate active restoration efforts, and where native remnants may be most vulnerable.

Restoration Within Protected Areas: When and How to Intervene to Manage Plant Invasions?

Despite the on-going efforts to set aside land for conservation, biodiversity is increasingly being threatened by factors such as invasive alien species that do not recognise these boundaries. Invasive species management programmes are widely incorporated into protected area management plans; however, the success of these programmes hinges on the ability to identify when a system will be able to recover after invader control and eradication efforts and when further intervention will be necessary to aide recovery. Invasive alien plants can alter ecosystem attributes to produce strong legacy effects that prevent the recovery of a system. Here we provide a framework for how to identify and incorporate recovery constraints into restoration efforts. Identifying recovery constraints can help improve how ecological theory – assembly rules, ecological succession, and threshold dynamics – can be used to guide restoration efforts.