Impact of plant cover on the cavity‐nesting ant Temnothorax crassispinus

1. Plant communities influence the availability of important resources for ants, such as nest sites and food, as well as environmental conditions. Thus, plants affect the abundance and distribution of ants. 2. In a field experiment, the influence of plant cover on the settlement of nest sites and per‐capita productivity of sexual individuals by the ant Temnothorax crassispinus was analysed. In July 2014, in five areas with patches of alien balsam Impatiens parviflora, and another five of native balsam I. noli‐tangere, transects composed of artificial nests were established; the nest sites were situated inside patches of balsams, and outside of them. Four hundred and forty artificial nests were used. One year later, the nests were collected. 3. Colonies of the ants three times more often inhabited nest sites outside the patches of both balsams. Besides, colonies with queens were more frequently found in nest sites located away from balsams. The per‐capita productivity of sexual individuals was higher in nests collected in patches of balsam, and the colonies from patches of alien balsam produced a more female‐biased sex ratio. 4. In terms of the impact on the ant, no clear differences were found between the alien balsam and the native one. The most important factor affecting the fitness of ants in areas dominated by balsams is the presence of herbaceous plant cover rather than whether the plant is alien or native.     

Direct and indirect effects of soil structure on the density of an antlion larva in a tropical dry forest

Abstract.  1. We used structural equation models to discriminate direct and indirect effects of soil structure on the abundance of the antlion Myrmeleon crudelis , a neuropteran larva that digs conical pits in soil to capture small arthropods. We proposed that soil structure may modify antlion density indirectly through its influence on tree cover, which in turn directly alters the amount of sun and rain that can reach the forest floor and the amount of litter fall.
2. The proportion of finer soils positively affected antlion density directly, but negatively tree cover. Tree cover positively affected both the amount of leaf litter and antlion density. Leaf litter negatively affected antlion density. The indirect effects of soils varied in strength and sign depending on whether trees are considered shelters against sun and rain, or leaf litter sources. The relative importance of these effects might also vary between years and seasons.
3. Antlions may select patches of finer soils not only because they are easy substrates in which to build pits, but also for their indirect benefit as sites with low leaf litter, illustrating how indirect interactions may affect the local abundance of semi-sedentary insects.     

Bait Uptake and Caching by Red Foxes and Nontarget Species in Urban Reserves

Abstract: The management of biodiversity in urban areas provides a challenge for conservation managers who are interested in the recovery of native species by controlling exotic species. Exotic-animal control programs using poisons can be contentious in terms of the health and safety of nontarget species, including people. Managing exotic predators in urban areas must be effective at 2 levels: controlling the target species and minimizing impacts to nontarget species. We investigated the feasibility of instigating a poison-baiting program to control nonindigenous European red foxes (Vulpes vulpes) in city conservation reserves (Perth, Australia). We selected 3 reserves to assess the safety and efficacy of baiting for foxes by maximizing bait uptake by the target species, and minimizing uptake by nontarget species. We tested 2 types of meat bait using 4 bait presentation methods (untethered, uncovered; untethered, covered; tethered, uncovered; tethered, covered). Bait uptake by foxes was highest in urban reserves compared to that in a peri-urban reserve. Bait type and presentation method equally explained bait uptake by foxes. Untethered and uncovered baits were removed 10% more often by foxes, and untethered baits had been cached more often than tethered baits. Baits cached by foxes for up to 1 week were not removed by species other than foxes. Domestic dogs and native birds were common nontarget species to remove baits. Dogs showed no aversion to removing any bait type, nor did bait presentation method influence bait removal. Birds removed fewer baits that had been tethered and covered. We provide an evidence base to demonstrate that bait uptake by nontarget species can be minimized, although we suggest that a fox control program is likely to be more of an organizational challenge to change public attitudes toward responsible dog ownership rather than a technical challenge to poison foxes.     

Effect of the canopy of Retama sphaerocarpa on its understorey in a semiarid environment

1. A dense understorey of annual and perennial herbs grow under the canopy of Retama sphaerocarpa shrubs in semiarid environments of south-east Spain, influencing plant productivity and diversity at a regional scale. We investigated the facilitation by the shrub on its understorey in field and laboratory experiments with Barley designed to explore the mechanisms of interaction between both vegetation layers and their spatial variation.
2. There was a gradient of spatial heterogeneity in soil chemical fertility under the shrub canopy, with organic matter and soil nitrogen contents higher at the centre than at the edge of the canopy. Dry mass production of Barley was also higher in soils from intermediate positions, and lower in soils from both the centre and edge of the canopy.
3. In the field, pots sown with Barley placed near the centre, at an intermediate position and at the edge of the canopy of Retama shrubs showed significant differences in productivity, suggesting a mulching effect of the canopy that also affects seedling establishment.
4. Micro-climatic measurements showed significant differences in total radiation reaching the soil, mean air and soil temperatures and maximum temperature among different positions in the understorey, increasing radially from the centre to the edge of the canopy.
5. These results and field observations suggest that the optimal association of climatic factors under the canopy would combine with a high soil fertility mediated by litter decomposition to increase biomass production mid-way between the centre and the edge of the canopy. Overstorey and understorey thus interact to increase nutrient retention locally, which benefits both the shrub and the herb layer.     

Organic Matter and Nitrogen Cycles in a Pine Afforested Catchment with a Shrub Layer of Adenocarpus decorticans and Cistus laurifolius in South-eastern Spain

Organic matter and nitrogen cycles in two mediterranean woodyshrubs (Adenocarpus decorticans Boiss. andCistus laurifoliusL.) and two pine species were investigated during 1987–1989in a small, recently pine-afforested catchment in Sierra delos Filabres (Almería Province, south-eastern Spain).Pine cover was sparse because canopy closure was not yet completed,allowing strong shrub colonization in the clearings. The aimof this study was to compare the contribution of different annualfluxes and the distribution of organic matter and nitrogen inboth shrub and pine components for the entire catchment. Specialemphasis was placed on the N use strategy shown by the two shrubspecies, a symbiotic N₂fixing species (A. decorticans) and anon-fixing species (C. laurifolius). Our results showed that the characteristics of C and N cyclingin the Nacimiento catchment are mainly determined by the earlystage of pine layer development and the significant contributionof the two shrub species differing with respect to C acquisitionand N use. The pine layer was characterized by a low standing biomass,substantial percentages of needle biomass and high (net production/biomass)and (needle production/total net production) ratios. N uptakewas mainly diverted to biomass increment, as shown by the substantialallocation found in this study. Overall, these results are consistentwith the patterns described for even-aged stands during theearly-growth phase. Retranslocation supplied 21% of the annualN requirements for pine above-ground biomass production. C. laurifolius showed low litter-fall return, strong retranslocation,efficient utilization of N in bulk deposition and slow decomposition,suggesting a closer, self-regulated organic matter and N-conservingbehaviour thanA. decorticans . On the contrary,A. decorticansshowed high leaf turnover, strong litter-fall return, low retranslocationand fast mineralization of organic matter and nitrogen, indicatingthat internal organic matter and N cycling is less efficient,and thus, that this species is more dependent on the soil tomeet its N requirements. Adenocarpus decorticans Boiss.; biogeochemical cycles,Cistus laurifolius L.; mediterranean shrubs; nitrogen fixation; nitrogen use; pine afforestation; south-eastern Spain; woody legumes