Competition for water and species coexistence in phenologically structured annual plant communities

Both competition for water and phenological variation are important determinants of plant community structure, but ecologists lack a synthetic theory for how they affect coexistence outcomes. We developed an analytically tractable model of water competition for Mediterranean annual communities and demonstrate that variation in phenology alone can maintain high diversity in spatially homogenous assemblages of water-limited plants. We modeled a system where all water arrives early in the season and species vary in their ability to grow under drying conditions. As a consequence, species differ in growing season length, and compete by shortening the growing season of their competitors. This model replicates and offers mechanistic explanations for qualitative patterns observed in prior empirical studies of how phenology influences coexistence among Mediterranean annuals. Additionally, we found that a decreasing, concave-up tradeoff between growth rate and access to water can theoretically maintain infinite diversity under simple but realistic assumptions. High diversity is possible because: 1) later plants escape competition after their earlier-season competitors have gone to seed and 2) early- season species are more than compensated for their shortened growing season by a growth-rate advantage. Together, these mechanisms provide an explanation for how annual plant species might coexist when competing only for water.

Looking for a successful translocation: the case of Astragalus edulis

Astragalus edulis (Fabaceae) is an endangered annual plant species from the western Mediterranean region. It occurs in the Iberian Peninsula (SE), Morocco (two main locations in the NE and SW), and the easternmost Canary Islands (Lanzarote and Fuerteventura). After a thorough study assessing genetic diversity and phylogeographic patterns, and a proposal of a management plan to preserve the genetic diversity across the entire area of the species, it is about time to go further in the species conservation. It is necessary to recognize genetically impoverished populations to be able to successfully reinforce populations and find realistic places for translocations. For this, Nei’s genetic diversity values were calculated for the three geographic areas and for their populations. Diversity values were further evaluated to calculate the optimal contribution for the populations within each area to maximize the genetic pool. To evaluate whether the optimum habitat for the species is expected to grow or decrease under a climate change scenario, the optimal model of current climatic suitability of A. edulis was projected into the IPCC (2070_RCP8.5) future scenario. The different geographical areas showed similar genetic diversity values. The populations that contribute to maximize the genetic pool in each geographic area were similar, but not equal, to those proposed in previous studies. The future potential habitat for the species shows a significant range decline, which will affect translocation efforts.

Variable Seed Bed Microsite Conditions and Light Influence Germination in Australian Winter Annuals

Environmentally-cued germination may play an important role in promoting coexistence in Mediterranean annual plant systems if it causes niche differentiation across heterogenous microsite conditions. In this study, we tested how microsite conditions experienced by seeds in the field and light conditions in the laboratory influenced germination in twelve common annual plant species occurring in the understorey of the York gum-jam woodlands in southwest Western Australia. Specifically, we hypothesized that if germination promotes spatial niche differentiation then we should observe species-specific germination responses to light. In addition, we hypothesized that species’ laboratory germination response may depend on the microsite conditions experienced by seeds while buried. We tested the laboratory germination response of seeds of species under diurnally fluctuating light and complete darkness which were retrieved from microsites spanning local-scale environmental gradients known to influence community structure in this system. We found that seeds of six out of the twelve focal species exhibited significant positive germination responses to light but that the magnitude of these responses varied greatly. In addition, maximum germinability increased significantly across a gradient of canopy cover for two species, but we found little evidence to suggest that species’ relative light requirement for germination varied depending on microsite conditions. Our results suggest that variability in light availability may promote coexistence in this system and that the microsite conditions seeds experience in the intra-growing season period can further nuance species germination behaviour.

Micro-climatic effects on plant phenolics at the community level in a Mediterranean savanna

Research has shown that warming and drought change plant phenolics. However, much of this work has centered on the effects of individual abiotic stressors on single plant species rather than the concurrent effects of multiple stressors at the plant community level. To address this gap, we manipulated rainfall and air temperature to test for their individual and interactive effects on the expression of leaf phenolics at the community level for annual plant species occurring in two habitat types (under oak tree canopies or in open grasslands) in a Mediterranean savanna. We found that augmented temperature had a significant positive effect on the community-weighted mean of total phenolics whereas reduced rainfall had no effect. In addition, we found no evidence of interactive effects between climatic stressors and these patterns remained consistent across habitat types. Overall, this study points at increasing efforts to investigate the linkages between climate change and community-level shifts in plant secondary chemistry.

The effects of precipitation variability on the canopy cover of forage species in arid rangelands, Iran

This research was conducted to monitor changes in canopy cover of typical species during a 10-year period in the part of arid rangelands, to find out the relationship between two important climate variables (precipitation and temperature) and canopy cover changes. For that reason, canopy cover percentages of six dominant perennials and all annual plant species combined were measured during a 10-year period at phenological maturity of plant in thirty 2 m × 2 m plots which were placed along two 250-m transect lines. The results demonstrated that the maximum canopy cover for water year 2006–2007 (wet year) and the minimum value for water year 2012–2013 (drought) were 15 and 5.5%, respectively. The canopy cover was modeled by linear regression in which precipitation and temperature variables were considered independent variables. April precipitation explained 65% of changes in the canopy cover percentage of Artemisia sieberi at 95% confidence level (RRMSE = 0.26 and MAE = 0.49). The best simple linear regression models for estimating canopy cover percentages of Stipa barbata and Zygophyllum eurypterum corresponded to cumulative 4-month precipitation from March to June and March precipitation respectively, representing 77% (at 99% confidence level) and 67% (at 95% confidence level) of changes correspondingly. Considering the dominance of A. sieberi, S. barbata, and Z. eurypterum in floristic composition of the study area, it can be concluded that most changes in canopy cover of the studied rangeland are predicted by variability of precipitation during growing seasons.

Response of Common Garden Annuals to Sublethal Rates of 2,4-D and Dicamba with or without Glyphosate

An experiment was conducted in 2017 and 2018 to determine the sensitivity of common garden annuals to sublethal rates of 2,4-dichlorophenoxyacetic acid (2,4-D) and dicamba with or without glyphosate. Sublethal rates corresponding to 1/10×, 1/100×, and 1/300× of the full labeled rate (1×) of 2,4-D (1.0 lb/acre), 2,4-D plus glyphosate (1.0 lb/acre plus 1.0 lb/acre), dicamba (0.5 lb/acre), and dicamba plus glyphosate (0.5 lb/acre plus 1.0 lb/acre) were applied to ‘Prelude’ wax begonia (Begonia ×semperflorens-cultorum), ‘Wizard’ coleus (Solenostemon scutellarioides), ‘Pinto’ zonal geranium (Pelargonium ×hortorum), ‘Dazzler’ impatiens (Impatiens walleriana), ‘Bonanza’ french marigold (Tagetes patula), ‘Hurrah’ petunia (Petunia hybrida), ‘Titan’ madagascar periwinkle (Catharanthus roseus), and ‘Double Zahara’ zinnia (Zinnia marylandica). Visible injury, plant height, number of flowers, and dry weight were recorded at specific time intervals after treatment. When averaged across all annual plant species, the 1/10× rate of 2,4-D plus glyphosate resulted in 51% injury 28 days after treatment, whereas the 1/10× rate of dicamba plus glyphosate resulted in 43% injury. Treatments causing the greatest injury also resulted in the greatest reduction of dry weight, height, and flower production. Coleus was the most sensitive species in the study; dry weight was reduced by 16% and 18% compared with the nontreated controls from 1/300× rates of 2,4-D plus glyphosate and dicamba plus glyphosate, respectively. French marigold and zonal geranium had greater sensitivity to treatments containing 2,4-D, but coleus and zinnia had greater sensitivity to treatments containing dicamba. Petunia exhibited a high tolerance to 2,4-D or dicamba applied alone (>6% injury) but was highly sensitive when glyphosate was added to 2,4-D and dicamba (<65% injury). The 1/100× and 1/300× rates that are likely to equate to sublethal rates in field settings, resulted in less than 15% injury across all flower species except coleus and petunia.

Mechanisms underlying higher order interactions: from quantitative definitions to ecological processes

When species simultaneously compete with two or more species of competitor, higher order interactions (HOIs) can lead to emergent properties not present when species interact in isolated pairs. In order to extend ecological theory to multi-competitor communities, ecologists must develop a practical and general definition for HOIs that can be applied to a wide range of competition models. In this paper we propose a definition for HOIs and outline a set of criteria for testing whether a model has or does not have HOIs. These criteria are valuable for empirical ecologists in need of clarity when discussing HOIs in empirical data. We also provide thorough discussion of how our definition compares with previous definitions of HOIs and interaction modification in the literature. In the second part of the paper we demonstrate the steps required for a rigorous test of HOIs in empirical data. To do this we simulate resource competition between three annual plant species which differ in phenology. We then fit phenomenological competition models to the outcome of simulated competition and use these to test for the presence of HOIs. In our simulations, we find the strength of HOIs varies with phenology: species that grow later experience stronger HOIs than earlier growing species. Our simulation shows how HOIs could emerge in ecosystems where resource availability and individual size change rapidly throughout the course of the growing season and where there are differences in the timing of resource acquisition between competitors.

Galium divaricatum Pourr. ex Lam. (Rubiaceae) – a new species for the flora of Ukraine

Galium divaricatum Pourr. ex Lam. is an annual plant species occurring mainly in dry grasslands. The centre of its distribution range is situated in the Mediterranean region, while in Central Europe it has been known only from a few isolated sites in Slovakia and Hungary. In 2016 we discovered this species in open dry grassland of the class Sedo-Scleranthetea on the upper edge of a basaltic andesite quarry near the village of Siltse, Irshavskyi District, Zakarpatska Region, as a new species for the Ukrainian flora. The site is situated in the transitional region between the Pannonian Basin and the Eastern Carpathians. The new locality represents the northernmost recent occurrence of this species.