Introduction to the Special Issue of Plants on "Advances in Plant Reproductive Ecology and Conservation Biology".

Plant reproductive ecology explores aspects of the biology and ecology of plants ranging from breeding systems, plant-pollinator interactions, seed germination, floral traits, and much more [...].

Assessing the Reproductive Ecology of a Rare Mint, Macbridea alba, an Endangered Species Act Protected Species.

Many rare plant species lack up-to-date research about their reproductive ecology, which challenges effective in situ and ex situ conservation, particularly in the face of ongoing environmental and anthropogenic changes. For protected species, outdated and incomplete information also creates barriers to successful recovery planning and delisting. In this study, we gathered a range of reproductive metrics for the federally threatened and state endangered Florida endemic mint, Macbridea alba Chapman (Lamiaceae). We collected data at seven populations within Apalachicola National Forest (Florida, USA) and conducted germination trials to estimate reproductive potential. Additionally, we observed a previously undocumented lepidopteran seed predator for the species and confirmed the occurrence of vivipary. The seed set was low with less than 20% of flowers per inflorescence producing seed across populations; however, germination was high with more than 60% of seeds germinating in five of seven populations. When comparing our results to previous research conducted more than 20 years ago, the results were similar overall (i.e., germination, vivipary); however, new information emerged (i.e., herbivore pressure). As M. alba undergoes reassessment as a potential candidate for delisting from the Endangered Species Act (ESA) list, this information is critical for assessing recovery goals and decisions regarding the species' protected status. For recovery needs related to propagation and reintroduction, these results can inform future seed collection and propagation efforts for the species.

Extensive regional variation in the phenology of insects and their response to temperature across North America.

Climate change models often assume similar responses to temperatures across the range of a species, but local adaptation or phenotypic plasticity can lead plants and animals to respond differently to temperature in different parts of their range. To date, there have been few tests of this assumption at the scale of continents, so it is unclear if this is a large-scale problem. Here, we examined the assumption that insect taxa show similar responses to temperature at 96 sites in grassy habitats across North America. We sampled insects with Malaise traps during 2019-2021 (N = 1041 samples) and examined the biomass of insects in relation to temperature and time of season. Our samples mostly contained Diptera (33%), Lepidoptera (19%), Hymenoptera (18%), and Coleoptera (10%). We found strong regional differences in the phenology of insects and their response to temperature, even within the same taxonomic group, habitat type, and time of season. For example, the biomass of nematoceran flies increased across the season in the central part of the continent, but it only showed a small increase in the Northeast and a seasonal decline in the Southeast and West. At a smaller scale, insect biomass at different traps operating on the same days was correlated up to ~75 km apart. Large-scale geographic and phenological variation in insect biomass and abundance has not been studied well, and it is a major source of controversy in previous analyses of insect declines that have aggregated studies from different locations and time periods. Our study illustrates that large-scale predictions about changes in insect populations, and their causes, will need to incorporate regional and taxonomic differences in the response to temperature.

Environmental DNA as an emerging tool in botanical research.

Over the past quarter century, environmental DNA (eDNA) has been ascendant as a tool to detect, measure, and monitor biodiversity (species and communities), as a means of elucidating biological interaction networks, and as a window into understanding past patterns of biodiversity. However, only recently has the potential of eDNA been realized in the botanical world. Here we synthesize the state of eDNA applications in botanical systems with emphases on aquatic, ancient, contemporary sediment, and airborne systems, and focusing on both single-species approaches and multispecies community metabarcoding. Further, we describe how abiotic and biotic factors, taxonomic resolution, primer choice, spatiotemporal scales, and relative abundance influence the utilization and interpretation of airborne eDNA results. Lastly, we explore several areas and opportunities for further development of eDNA tools for plants, advancing our knowledge and understanding of the efficacy, utility, and cost-effectiveness, and ultimately facilitating increased adoption of eDNA analyses in botanical systems.

Camera traps are an effective tool for monitoring insect-plant interactions.

Insect and pollinator populations are vitally important to the health of ecosystems, food production, and economic stability, but are declining worldwide. New, cheap, and simple monitoring methods are necessary to inform management actions and should be available to researchers around the world. Here, we evaluate the efficacy of a commercially available, close-focus automated camera trap to monitor insect-plant interactions and insect behavior. We compared two video settings-scheduled and motion-activated-to a traditional human observation method. Our results show that camera traps with scheduled video settings detected more insects overall than humans, but relative performance varied by insect order. Scheduled cameras significantly outperformed motion-activated cameras, detecting more insects of all orders and size classes. We conclude that scheduled camera traps are an effective and relatively inexpensive tool for monitoring interactions between plants and insects of all size classes, and their ease of accessibility and set-up allows for the potential of widespread use. The digital format of video also offers the benefits of recording, sharing, and verifying observations.

Can floral display size compensate for Allee effects caused by low population abundance and density in Synthyris bullii (Plantaginaceae), a rare species?

PREMISE OF THE STUDY: Conservation seeks to address the issues of small population size, and the reproductive limitations confronting these populations. Sparse, small plant populations often suffer Allee effects such as pollinator limitation. However, some studies show that plants in sparse populations experience reduced resource competition. As a result, these plants may produce larger floral displays, which are also predicted to attract pollinators. The negative impacts from reduced floral quantity may thus be offset by improved floral quality. METHODS: In a 2-yr field study, population abundance and density were quantified for 24 populations of Synthyris bullii (Plantaginaceae), a rare prairie endemic. In each population, data were collected on inflorescence size, fruit/seed set, and seed germination. KEY RESULTS: Inflorescence size had a positive relationship with population inflorescence abundance and density. Fruit set and germination responded positively to floral quality (i.e., flower density). In comparison, seed set showed a positive relationship with only floral quantity (i.e., population abundance). CONCLUSIONS: Contrary to our predictions, inflorescence size and population size were not inversely related. While attractive floral displays in sparse populations potentially compensate in terms of fruit set, population abundance nevertheless plays an important role in seed set. Because floral quality and quantity differ in their ability to explain reproductive outcomes, studies should examine reproduction at several stages, otherwise the impacts of population size may be overlooked. Allee effects manifesting at a critical stage of reproduction, such as seed production, may act as a bottleneck impeding successful recruitment.