Progress on Mechanisms and Impacts of Wetland Plant Invasions: A Twenty-Year Retrospective Analysis and Priorities for the Next Twenty

Stephen M. Hovick, Carrie Reinhardt Adams, Neil O. Anderson & Karin M. Kettenring. 2023. Critical Reviews in Plant Sciences, DOI: 10.1080/07352689.2023.2233232

Abstract

Invasive plants are ubiquitous features of many wetland systems, resulting in impacts that are extremely costly in both economic and ecological terms. Approximately twenty years ago, these impacts and many of the mechanisms underlying invasion were crystallized in a pair of now-classic review papers on the topic. These two contributions have guided sub- stantial research efforts over the past two decades. Here, using a state-of-the-art review, we present an overview of research progress from the past 20 years and identify research prior- ities for the next 20 years. We structure these insights around key themes that emerge from those earlier reviews and emphasize ways wetland invasions might be distinguished from plant invasions in uplands. We first highlight research progress and priorities around the impacts of wetland plant invasions. We then do the same for seven broad mechanisms that have been postulated to enhance invasion success in wetlands. Invasive plants clearly impact wetlands across all levels of ecological organization and up to landscape scales, but generalizable conclusions are still lacking concerning what drives variation in impact magni- tudes. One of the key mechanisms underlying invasion success reflects site-level variation in resource availability and, although we know that increased resources often lead to more opportunities for invasion, the role of discrete resource pulses and the way resource avail- ability may interact with propagule pressure variability are poorly understood. Second, although release from natural enemies is a long-held potential driver of invasion success, recent insights support speculation that these effects may be especially pronounced in wet- lands. Third, although most invasive wetland plants are considered good competitors, their simultaneous role as stress tolerators raises questions about whether expectations regarding life history tradeoffs may be less applicable for wetland invaders than for the upland species around which these theories were designed. Fourth, despite a keen understanding that wet- land plant invaders are opportunistic, establishing quickly in response to disturbance, the central importance of seed and seedling traits has not been adequately studied to integrate life history theory across ontogenetic stages. Fifth, although many invasive wetland plants reproduce both sexually and asexually, the extent to which this mixed strategy contributes to their success as invaders has not been rigorously assessed. Sixth, despite observations that wetland invaders often exhibit a high degree of phenotypic variability, causal connec- tions between the success of wetland invaders and either high population genetic diversity or high phenotypic plasticity have not been clearly established. Lastly, despite long-standing interests in whether interspecific hybridization contributes to wetland invader success, recent studies have highlighted evolutionary processes leading to variation in polyploidy and genome size as alternatives requiring additional study. We conclude with a vision for prioritizing wetland plant invasions research, presenting insights from this review aimed at inspiring future studies on remaining key uncertainties regarding the relative impacts of wetland vs. upland invaders and the relative importance of phenotypic plasticity, population genetic diversity, enemy release, and anthropogenic disturbances for influencing the success of invasive plants in wetland vs. upland systems.

SAviTraits 1.0: Seasonally varying dietary attributes for birds

Stephen J. Murphy, André M. Bellvé, Reymond J. Miyajima, Natalie A. Sebunia, Molly M. Lynch, Walter Jetz, Marta A. Jarzyna. 2023. https://doi.org/10.1111/geb.13738

Abstract

Trait-based studies remain limited by the quality and scope of the underlying trait data available. Most of the existing trait databases treat species traits as fixed across time, with any potential temporal variation in the measured traits being unavailable. This is despite the fact that many species are well known to show plasticity in their trait characteristics over the course of the year. This data paper describes a compilation of species-specific dietary preferences and their known intra-annual variation for over 10,000 of the world's extant bird species (SAviTraits 1.0). Information on dietary preferences was obtained from the Cornell Lab of Ornithology Birds of the World (BOW) online database. Textual descriptions of species' dietary preferences were translated into semi-quantitative information denoting the proportion of dietary categories utilized by each species. Temporal variation in dietary attributes was captured at a monthly temporal resolution. We describe the methods for data discovery and translation and present tools for summarizing the annual variability of avian dietary preferences. Altogether, we were able to document a seasonal variability in dietary attributes for a total of 1031 species (ca. 10%). For the remaining species, the dietary attributes were either temporally stationary or the information on temporal variability of the diet was not available.

Coupled Demographic Dynamics of Herds and Households Constrain Livestock Population Growth in Pastoral Systems

Mark Moritz, Chelsea E. Hunter, Daniel C. Peart, Abigail Buffington, Andrew J. Yoak, Jason R. Thomas, Rebecca Garabed & Ian M. Hamilton. Human Ecology volume 51, pages 641–653 (2023).

Abstract

One of the dominant narratives about pastoral systems is that livestock populations have the potential to grow exponentially and destroy common-pool grazing resources. However, longitudinal, interdisciplinary research has shown that pastoralists are able to sustainably manage common-pool resources and that livestock populations are not growing exponentially. The common explanation for limits on livestock population growth is that reoccurring droughts, diseases, and other disasters keep populations in check. However, we hypothesize that coupled demographic processes at the level of the household also may keep livestock population growth in check. Our hypothesis is that two mechanisms at the herd-household level explain why livestock populations grow much slower in pastoral systems than predicted by conventional Malthusian models. The two mechanisms are: (1) the domestic cycle of the household, and (2) the effects of scale and stochasticity. We developed an agent-based model of a pastoral system to evaluate the hypothesis. The results from our simulations show that the couplings between herd and household do indeed constrain the growth of both human and livestock populations. In particular, the domestic cycle of the household limits herd growth and ultimately constrains the growth of livestock populations. The study shows that the misfortunes that affect individual households every day cumulatively have a major impact on the growth of human and livestock populations.

Reclaiming urban vacant land to manage stormwater and support insect habitat

Michelle A. Pham, MaLisa R. Spring, Frances S. Sivakoff & Mary M. Gardiner 
Urban Ecosystems (2023). 

Abstract

Urban green spaces can provide important wildlife habitat and ecosystem services. In legacy cities, built structures are demolished as populations dwindle, resulting in vacant land. Vacant land constitutes an opportunity to establish green infrastructure that provides multiple ecosystem services. Our objective was to determine whether establishing green infrastructure on vacant land to manage stormwater could provide insect habitat in the legacy city of Cleveland, Ohio, U.S.A. Two green infrastructure treatments were implemented on vacant land in the historic Slavic Village neighborhood in 2014 and 2015: rain gardens (lower cost) and bioswales (higher cost). We hypothesized that rain gardens and bioswales would support more abundant, species rich insect communities compared to unaltered vacant lots. Wild bees (Hymenoptera: Aculeata) and lady beetles (Coleoptera: Coccinellidae), two insect groups of conservation concern, were sampled during the summer (June–August) from 2014 to 2016 using pan traps and yellow sticky card traps. Local vegetation and temporal variables were measured. Generalized linear mixed effects models evaluated whether insect biodiversity varied with treatment, habitat variables, site, and time. We collected 3,004 bees from pan traps and 5,438 lady beetles from yellow sticky card traps during this study. Bee biodiversity was similar among treatments. In 2014, alien Coccinellidae abundance was higher in vacant lots compared to rain gardens. In 2015 and 2016, alien Coccinellidae were marginally more abundant in rain gardens compared to vacant lots and bioswales, while native Coccinellidae abundance was significantly higher in vacant lots. In the short term, establishing green infrastructure on vacant land can improve stormwater management without compromising the quality of vacant land as insect habitat.