This is the first study to evaluate the phytotoxic activity of three phenolic compounds present in the essential oil of the labdanum of Cistus ladanifer, an allelopathic species of the Mediterranean ecosystem. Propiophenone, 4′-methylacetophenone, and 2′,4′-dimethylacetophenone slightly inhibit total germination and radicle growth of Lactuca sativa, and they strongly delay germination and reduce hypocotyl size. On the other hand, the inhibition effect of these compounds on Allium cepa was stronger on total germination than on germination rate, and radicle length compared to hypocotyl size. The position and number of methyl groups will affect the efficacy of the derivative. 2′,4′-dimethylacetophenone was the most phytotoxic compound. The activity of the compounds depended on their concentration and presented hormetic effects. In L. sativa, on paper, propiophenone presented greater inhibition of hypocotyl size at greater concentrations, with IC50 = 0.1 mM, whereas 4′-methylacetophenone obtained IC50 = 0.4 mM for germination rate. When the mixture of the three compounds was applied, in L. sativa, on paper, the inhibition effect on total germination and the germination rate was significantly greater compared to the effect of the compounds when they were applied separately; moreover, the mixture inhibited radicle growth, whereas propiophenone and 4′-methylacetophenone did not exert such effect when applied separately. The activity of the pure compounds and that of the mixture also changed based on the substrate used. When the trial was conducted in soil, the separate compounds delayed the germination of the A. cepa to a greater extent compared to the trial on paper, although they stimulated seedling growth. In soil, L. sativa against 4′-methylacetophenone also showed the opposite effect at low concentrations (0.1 mM), with stimulation of germination rate, whereas propiophenone and 4′-methylacetophenone presented a slightly increased effect.

1. Animals often face a trade-off between food acquisition and predation/disturbance avoidance. Yet, the extent to which this trade-off is affected by modulating factors such as thermal risk and foraging opportunities has been largely overlooked.2. Here, we examined the influence of temporal and environmental gradients on the flight initiation distance (FID, the distance at which animals flee from an approaching human-simulated predator) and escape mode (flying/low risk versus running/low cost) in 16 species of shorebirds foraging on tidal flats of the Bijagós Archipelago, Guinea-Bissau. We measured escape responses throughout the low tide period during wet and dry seasons and simultaneously recorded microclimate variables and occurrence of heat-reduction behaviour (ptiloerection). Furthermore, we measured corticosterone metabolites (CORTm) from droppings in red knots Calidris canutus to assess whether ptiloerection is associated to a physiological stress response to hot conditions.3. Overall, birds tolerated a closer approach at higher environmental temperatures and when showing ptiloerection. They also had shorter FIDs during the dry season and towards the start/end of the low tide period. FIDs also increased with body mass and decreased in areas with more human presence. In red knots, individuals showing ptiloerection had higher levels of CORTm, demonstrating a link between physiological and behavioural stress coping responses to heat events. 4. Our results suggest that heat-stressed shorebirds take greater risks, supporting the idea of a thermoregulation-predation risk trade-off. They also indicate that shorebirds adjust risk taking to tidal and seasonal cycles, generally reducing FIDs when the energetic costs of escape are expected to be large. Finally, they suggest that shorebirds habituate to non-lethal human presence and respond to perceived predation risk in accordance with the predictions of optimal escape theory.5. These results are relevant to many animals that face a tight window for foraging activity while being exposed to predation/disturbance and heat during the day. We discuss management implications of our results in the context of global change.