Identifying the factors modulating range expansion is essential to accurately predict changes in the spatial distribution of populations. By preventing population growth after dispersal, Allee effects can lead to front stops in discrete space, called 'pinning' if permanent. However, other mechanisms, such as positive density-dependent dispersal, have also been shown to affect the rate of range expansion and generate discrete-space front stops, albeit temporarily. In this study, we investigated the stability of the front stops generated by such mechanisms in relation to the carrying capacity of the environment. To this end, we performed artificial range expansions in discrete space using stochastic simulations and microcosm experiments. Simulation results confirmed that density-dependent dispersal alone can generate sustained front stops, albeit for a limited range of carrying capacities. We also highlighted the synergy between Allee effects and density-dependent dispersal on pinning emergence. Experimental results, obtained using a model species known to exhibit density-dependent dispersal, but without Allee effects, confirmed the model results. Furthermore, our study raises the issue of carefully considering the conditions for pinning stability, in a stochastic context and depending on the time-scale considered.

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Major traits defining the life history of organisms are often not independent from each other, with most of their variation aligning along key axes such as the pace-of-life axis. These axes, along with their potential associations or syndromes with other traits such as dispersal, are however not universal; in particular, support for their presence may be taxon and taxonomic scale-dependent. Knowing about such life-history strategies may be especially important for biological control agents, as these trait syndromes may constrain the ability to optimize production, as well as their efficiency in the field. To understand how life-history traits and dispersal covary in such contexts, we measured these traits in controlled conditions for 28 lines from 5 species ofTrichogramma, small endoparasitoid wasps frequently used against Lepidoptera pests. We found partial evidence of a pace-of-life axis at the interspecific level: species with higher fecundity also had faster development time. However, faster developing species also were more likely to delay egg-laying, a trait that is usually interpretable as "slow". There was no support for similar covariation patterns at the within-species line level. There was limited variation in dispersal between species and line, and accordingly, we did not detect any correlation between dispersal rates and life-history traits. We discuss how expanding our experimental design by accounting for the density-dependence of both the pace of life and dispersal might reveal a dispersal syndrome in future studies. Overall, our results highlight the importance of exploring covariation at the "right" taxonomic scale, or multiple taxonomic scales, to understand the (co)evolution of life history traits. They also suggest that optimizing all interesting life-history traits for inoculative releases may be difficult in programs using one species.