Propagule pressure and climate contribute to the displacement of Linepithema humile by Pachycondyla chinensis.

Identifying mechanisms governing the establishment and spread of invasive species is a fundamental challenge in invasion biology. Because species invasions are frequently observed only after the species presents an environmental threat, research identifying the contributing agents to dispersal and subsequent spread are confined to retrograde observations. Here, we use a combination of seasonal surveys and experimental approaches to test the relative importance of behavioral and abiotic factors in determining the local co-occurrence of two invasive ant species, the established Argentine ant (Linepithema humile Mayr) and the newly invasive Asian needle ant (Pachycondyla chinensis Emery). We show that the broader climatic envelope of P. chinensis enables it to establish earlier in the year than L. humile. We also demonstrate that increased P. chinensis propagule pressure during periods of L. humile scarcity contributes to successful P. chinensis early season establishment. Furthermore, we show that, although L. humile is the numerically superior and behaviorally dominant species at baits, P. chinensis is currently displacing L. humile across the invaded landscape. By identifying the features promoting the displacement of one invasive ant by another we can better understand both early determinants in the invasion process and factors limiting colony expansion and survival

Nest defense and survival of <i>L. humile</i> at various <i>P. chinensis ∶ L. humile</i> ratios with <i>L. humile</i> as resident or intruder.

<p>Data expressed as proportion of total replicates (±SE) (n = 12). Significant differences (displaced or surviving) within treatment columns (resident or intruder) are denoted by letters (Tukey-Kramer comparison of means, p<0.05).</p

Venn diagrams representing the number of locations with <i>L. humile</i> (blue) and <i>P. chinensis</i> (pink with dashed border), in 2008, 2009, 2010, and 2011.

<p>Overlapping circle areas represent tree bases with <i>P. chinensis/L.humile</i> species overlap. Numbers within circles depict the number of trees with each status (<i>P. chinensis-</i>only, <i>L. humile-</i>only, or <i>P. chinensis/L. humile</i> overlap) for each measurement period. In 2008 and 2009, there were no <i>P. chinensis-</i>only locations (inner circles depict species overlap locations).</p

The mean proportion (±SE) of baits discovered (A), mean proportion (±SE) of baits dominated (B) and time (mean ± SE minutes) to bait discovery (C) by <i>P. chinensis</i> and <i>L. humile</i> in areas of species overlap or non-overlap (*p<0.05, Tukey HSD ANOVA, within species comparison).

<p>The mean proportion (±SE) of baits discovered (A), mean proportion (±SE) of baits dominated (B) and time (mean ± SE minutes) to bait discovery (C) by <i>P. chinensis</i> and <i>L. humile</i> in areas of species overlap or non-overlap (*p<0.05, Tukey HSD ANOVA, within species comparison).</p

Seasonal abundance of <i>P. chinensis</i> and <i>L. humile</i>, with mean (±SE) clusters of ants at sampling sites each month and average maximum monthly temperature from March, 2009 to June, 2011.

<p>Black arrows indicate significant (PROC GLM p<0.001) numbers of <i>P. chinensis</i> (compared to previous month) and white arrows indicate significant (PROC GLM p<0.001) numbers of <i>L. humile</i> compared to that of prior month.</p

Survival of <i>P chinensis</i> at various <i>P. chinensis ∶ L. humile</i> ratios when <i>L. humile</i> is either the resident or intruder.

<p>Data expressed as mean proportion (±SE). Significant differences within treatment columns denoted by different letters (Tukey-Kramer comparison of means, p<0.05).</p

Mean (±SE) proportion of baits occupied by either <i>P. chinensis</i> (○) or <i>L. humile</i> (•) in plots chemically-treated to remove <i>P. chinensis</i> 0, 1, 3, and 14 days after treatment (χ²₁ = 9.82, p = 0.01).

<p>Mean (±SE) proportion of baits occupied by either <i>P. chinensis</i> (○) or <i>L. humile</i> (•) in plots chemically-treated to remove <i>P. chinensis</i> 0, 1, 3, and 14 days after treatment (χ²₁ = 9.82, p = 0.01).</p

A global assessment of the species composition and effectiveness of watermelon pollinators and the management strategies to inform effective pollination service delivery

For most food crops the identity and efficiency of pollinators across key growing regions remains a significant knowledge gap that needs to be addressed before we can develop crop-specific approaches for pollination service delivery. Here, we conducted a systematic literature review and meta-analysis on watermelon (Citrullus lanatus (Thunb. Matsum. & Nakai)), a globally important fruit crop, to identify the floral visitors and their efficiency across different growing regions. We found that 265 insect species visit watermelon flowers (including 5 orders, 18 families and 75 genera) across 17 countries and 6 continents. Bees and flies were the most abundant flower visitors overall, but show distinct regional differences. Honey bees were the majority visitor in 53% of growing regions (range: 0 – 94%), whilst wild bee species were more abundant in 42% of regions (range: 3.4 – 100%). Honey bees and other bees were equally effective at depositing pollen on stigmas, but varied in effectiveness for fruit set and seed set. Pollination data from global studies appear to be limited for the largest-scale watermelon producers, namely: China, Turkey, and India, with the majority (56%) of data available from North America. This synthesis identified four key themes for improving pollination in watermelon: increasing honey bee densities on crops where local polices and environmental conditions are suitable; introducing other managed pollinators; identifying key wild pollinator taxa to encourage within crops; and improving local and landscape management practices to support pollinators