Multitrophic higher-order interactions modulate species persistence

There is growing recognition that interactions between species pairs are modified in a multispecies context by the density of a third species. However, how these higher-order interactions (HOIs) affect species persistence remains poorly understood. To explore the effect of HOIs steaming from multiple trophic layers on plant persistence, we experimentally built a mutualistic system containing three plants and three pollinators species with two contrasting network structures. For both structures, we first estimated the statistically supported HOIs on plant species, in addition to the pairwise interactions among plants and plant-pollinators. Following a structuralist approach, we then assessed the effects of the supported HOIs on the persistence probability of each of the three competing plant species and their combinations. HOIs produced substantial effects on the strength and sign of per capita interactions between plant species to such an extent that predictions of species persistence differ from a non-HOIs scenario. Changes in network structure due to removing a plant-pollinator link further modulated the species persistence probabilities by reorganizing per capita interaction strengths of both pairwise interactions and HOIs. Our study provides empirical evidence of the joint importance of HOIs and network structure for determining the probability of species to persist within diverse communities.

Insularity forcing on plant persistence strategies in edaphic island systems

Aim: Trait-based approaches are increasingly implemented in island biogeography, providing key insights into the eco-evolutionary dynamics of insular systems. However, what determines persistence of plant species once they have arrived and established in an island remains largely unexplored. Here, we examined links between non-acquisitive persistence strategies and insularity across three terrestrial edaphic island systems, hypothesising that insularity promotes strategies for local persistence. Location: Europe: Western Carpathians, Moravia, and Cantabrian Range. Time period: Present. Major taxa studied: Vascular plants. Methods: For each system, we used linear models at the island scale to test whether persistence-related plant trait patterns (average trait values and diversity) depend on three insularity metrics (island size, isolation and target effect). We focused on patterns of edaphic island specialists because, in contrast to matrix-derived species, their presence is confined to the edaphic islands. Results: We found that insularity metrics explained large proportions in the variation of the average and diversity of persistence-related traits of edaphic island specialists. Insularity was associated with a decline in the proportion of island specialists that have clonal abilities, yet it affected trait values of specialists towards enhanced abilities to persist locally (e.g. more extensive lateral spread) while reducing trait variability. Higher degrees of insularity within the systems were translated to stronger effects on functional trait patterns. Main conclusions: Insularity affects plant species diversity, distribution and forms in terrestrial island-like systems, similarly as it is assumed for true islands. Insularity, measured using a single (island size, isolation) or combined (target effect) predictors, may operate selecting for enhanced and less diverse persistence strategies. Ultimately, this process, which we call insularity forcing, operates as a selective process to promote species ability to avoid local extinction and to persist on terrestrial islands.

87 Evaluation of two stocking rates for grazing heifers on mixed sward native warm-season grass pastures in the Black Belt Prairie region

Optimal use of native warm-season grasses in pasture systems involves stocking grazing livestock at suitable rates. The study objective was to evaluate forage nutritive value and heifer ADG at two stocking rates on mixed-sward pastures of big bluestem (Andropogon gerardi Vitman), little bluestem (Andropogon scoparius), and indiangrass (Sorghastrum nutans L.). Pastures (3 replications) were stocked for 56 d during June and July in 2 yr with crossbred (Bos taurus) heifers (n = 24 heifers/year) stratified by initial BW (288.3 ± 1.7 kg) to one of two continuous stocking rates: 1.9 heifers/ha (HIGH) and 1.2 heifers/ha (LOW). Mean forage nutritive values on a DM basis were not different between HIGH and LOW stocking rates, respectively, for CP (7.0 ± 0.2% vs 6.7 ± 0.2%; P = 0.27), ADF (41.0 ± 0.6 vs. 41.4 ± 0.6; P = 0.64), NDF (69.9 ± 0.5 vs. 68.7 ± 0.5; P = 0.09), or relative feed value (RFV) (76.0 ± 1.0 vs. 76.9 ± 1.0; P = 0.53). There was a year effect (P < 0.01) and stocking rate x day effect (P < 0.01) for TDN. At LOW, TDN decreased from day 0 to day 28 (P = 0.02) and day 28 to day 56 (P = 0.02). At HIGH, TDN decreased (P < 0.01) from day 0 to day 28 but remained steady until day 56 (P = 0.21). There was a stocking rate x day interaction (P < 0.01) with ADG: LOW day 28 to 56 (1.20 ± 0.08 kg/day), HIGH day 0 to 28 (0.89 ± 0.08 kg/day), HIGH day 28 to 56 (0.44 ± 0.08 kg/day), and LOW day 0 to 28 (0.30 ± 0.08 kg/day). Further assessment of cattle ADG using more divergent stocking rates and plant persistence measures is warranted to inform ideal native grass stocking rate recommendations.

Distribution of Asclepias Asymptomatic Virus and Exploration of Possible Effects on the Wild Plant Host, Asclepias viridis

Viruses in wild plants are poorly studied yet important sources of emerging diseases. We surveyed populations of a perennial host, Asclepias viridis, for Asclepias asymptomatic virus (AsAV) in nine sites (two in Oklahoma, seven in Kansas) from 2015 to 2018. All collected leaf samples from A. viridis were tested serologically by dot-immunobinding assays. In Oklahoma, the virus was present and abundant at both sites; in Kansas, the virus was found in four sites, but only one or two plants were infected per site. We followed the fate of individual plants and found little evidence that plant persistence or reproduction differed among plants with and without virus infection. Infected plants were 20% shorter than noninfected plants in two years at one site. No symptoms were evident in virus-infected plants. We observed apparent gains and losses of infection across years in Oklahoma but not in Kansas. The apparent neutral to slightly negative effects of this virus on this wild host emphasize the importance of studying wild plant–wild virus interactions to more fully understand plant virus ecology. Further, the fact that the virus is known to cause symptoms in plants of economically important families emphasizes the applied importance of research on wild viruses.

Establishment success and persistence of threatened plant translocations in south west Western Australia: an experimental approach

Establishment of viable threatened plant populations through translocations presents significant practical and logistical challenges. To address these challenges there is a need for experimental studies that inform refinement of translocation methodologies to optimise seedling survival during the establishment phase. In the present study we investigated the effect of three post planting techniques on the survival and growth of six translocated threatened plant species in south-west Western Australia over a 10-year period. Planted seedlings received summer watering for the first year, mulch or protection from vertebrate herbivores. Survival of seedlings was significantly enhanced in both watering and fencing treatments, but was not positively influenced by the mulch treatment. Plant growth was also significantly improved by the fencing treatment. Results showed that both fencing and supplementary summer watering were two very effective approaches for enhancing seedling establishment and plant persistence. We emphasise the value of integrating an experimental approach involving long-term monitoring into threatened plant species translocations and recovery programs for improving plant translocation success.

Assessing and overcoming genetic trade-offs in breeding grazing-tolerant lucerne

Selection of grazing-tolerant lucerne (Medicago sativa L.) for mild-winter environments is challenged by marked cold-season dormancy and prostrate habit often observed in tolerant material. This study aimed to assess the amount of genetic variation and genetically based trade-offs for key traits in four biparental populations, and their implications for selection. Some 432 cloned F1 progenies from four crosses between contrasting genotypes (erect, not very dormant, non-grazing tolerant v. prostrate, dormant, tolerant) were evaluated for dry matter (DM) yield and final plant persistence under continuous, intense sheep grazing for 3 years, along with a set of morpho-physiological traits. Both DM yield and persistence displayed negative genetic correlation with erect plant habit (rg –0.31 to –0.87, depending on the cross), with persistence inversely related also to cold-season growth (rg –0.33 to –0.73). Correlations of performance traits with DM yield before grazing management, plant diameter and leaflet area were inconsistent or nil. DM yield during grazing management and persistence exhibited large genetic variation (CVg 33.3–57.8%), and within-cross variance largely exceeded between-cross variance. Morpho-physiological traits had lower genetic variation and even greater relative within-cross variance than yield and persistence. Selection for grazing-tolerant germplasm could exploit large genetic variation, but it requires extensive within-cross genotype evaluation to produce material with little dormancy and relatively erect growth habit.