Increased abundance of native and non-native spiders with habitat fragmentation

Habitat fragmentation and invasive species often contribute to the decline of native taxa. Since the penetration of non‐native species into natural habitat may be facilitated by habitat fragmentation, it is important to examine how these two factors interact. Previous research documented that, in contrast to most other arthropod taxa, spiders increased in density and morphospecies richness with decreasing fragment area and increasing fragment age (time since insularization) in urban habitat fragments in San Diego County, California, USA. We tested whether a specific mechanism, an increase in non‐native species with fragmentation, is responsible for this pattern. We found that both native and non‐native taxa contributed to the pattern. Abundance of native spiders per pitfall trap sample increased significantly with decreasing fragment size (i.e. a negative density–area relationship) and abundance of non‐natives increased significantly with increasing fragment age. The proportion of non‐native individuals also increased significantly with age. One non‐native species, Oecobius navus, comprised the majority of non‐native individuals (82.2%) and a significant proportion of total individuals (25.1%). Richness of spider families per sample (family density) increased with fragment age due to an increase in the occurrence of non‐natives in older fragments, however, native family richness did not vary with age or area. Due to increasing dominance by non‐native and some native families, family evenness declined with decreasing fragment size and increasing fragment age. Native and non‐native abundance covaried positively arguing against strong negative interactions between the two groups. O. navus had a strong positive association with another common non‐native arthropod, the Argentine ant (Linepitheme humile), suggesting a possible direct interaction. In contrast, abundance of native spiders was negatively correlated with Argentine ant abundance. We hypothesize that fragmentation in this semiarid habitat increases productivity in smaller and older fragments enhancing the density of both native and non‐native taxa.     

Tropical ant communities are in long-term equilibrium

Communities change with time. Studying long-term change in community structure permits deeper understanding of community dynamics, and allows us to forecast community responses to perturbations at local (e.g. fire, secondary succession) and global (e.g. desertification, global warming) spatial scales. Monitoring efforts exploring the temporal dynamics of indicator taxa are therefore a critical part of conservation agendas. Here, the temporal dynamics of the Otongachi leaf litter ant community, occurring in a cloud forest in coastal Ecuador, were explored. By sampling this community six times over eleven years, I assessed how the ant fauna caught by Winkler traps (more diverse and cryptic fauna) and caught by pitfall traps (larger, more mobile fauna) changed over time. The Otongachi leaf litter ant community was dynamic. Although species richness in the community remained constant, temporal turnover of species was high: on average, 51% of the ant species in Winkler traps, and 56% of those in pitfall traps, were replaced with other ant species from one year to the other. Shifts in the rank abundance of species in the community were also large across the eleven years and, on average, shifts in the rank abundance of species collected by Winkler traps doubled those occurring in pitfall traps from one census to the other. In spite of these trends, the Otongachi ant fauna showed no (Winkler) or weak (pitfall) evidence of directional change (towards a new community). Thus, this tropical ant community can be divided in two community compartments. The Winkler compartment composed by a more diverse and cryptic ant fauna appears to be resilient and stable in time. The pitfall compartment composed by larger and more mobile ants may be prone to respond to disturbance. This study suggests that 1) species appearing/disappearing from a site may be rather the rule, difficult to separate from responses to ecological stress. 2) Conclusions made in short-term studies, or studies comparing two (e.g. before and after) snapshots of a community, should thus be revisited. Finally, 3) the ant fauna caught by pitfall traps (a rather simple and cheap survey method) is the most likely community compartment to indicate ecological perturbation. This study adds to the growing evidence that using ants as ecological indicators should incorporate long-term temporal dynamics.     

Two new myrmecophilous species of the genus Scutacarus (Acari: Prostigmata: Scutacaridae) with world keys to related species groups

In a survey on heterostigmatic mites (Acari: Prostigmata: Heterostigmata) associated with insects including ants in northwestern Iran, two new species of myrmecophilous mites of the genus Scutacarus (Acari: Scutacaridae) were found. They are S. shajariani sp. nov. phoretic on Tetramorium sp. (Hymenoptera: Formicidae) and S. ebermanni sp. nov. phoretic on Messor sp. The mentioned new species belong to groups of species with reduced setae e and h₂, and no setae 4b, respectively. These two new species are described and illustrated, and world keys are provided for respective species groups.     

Observations on the Ecology of Weaver Ants (Oecophylla smaragdina Fabricius) in a Thai Mangrove Ecosystem and Their Effect on Herbivory of Rhizophora mucronata Lam.

Ants of the genus Oecophylla are predators of other insects and are able to protect a variety of terrestrial plants against pest insects; however, observations on the ecology of these ants in mangrove forests are lacking. General observations on the ecology of Oecophylla smaragdina were carried out in a Thai mangrove forest to determine if these ants can protect their host plants in less favorable mangrove habitats. Leaf herbivory and the density of O. smaragdina ants were measured on Rhizophora mucronata trees at two sites. The results showed a negative correlation between ant density and herbivory. At both sites, the mean percent damaged leaf area was more than four times higher on trees without ants compared to “ant‐trees.” A significant negative correlation was found between tree mean percent leaf damage and the density of ants on the tree. Furthermore, on trees with ants, there was less herbivory on leaves close to ant nests compared to other leaves on the tree. Most damage was caused by chrysomelid beetles (62%) and sesarmid crabs (25%) and both types of herbivory were significantly reduced on ant‐trees.     

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.     

Shaking a leg and hot to trot: the effects of body size and temperature on running speed in ants

Abstract.  1. Data were compiled from the literature and our own studies on 24 ant species to characterise the effects of body size and temperature on forager running speed.
2. Running speed increases with temperature in a manner consistent with the effects of temperature on metabolic rate and the kinetic properties of muscles.
3. The exponent of the body mass-running speed allometry ranged from 0.14 to 0.34 with a central tendency of approximately 0.25. This body mass scaling is consistent with both the model of elastic similarity, and a model combining dynamic similarity with available metabolic power.
4. Even after controlling for body size or temperature, a substantial amount of inter-specific variation in running speed remains. Species with certain lifestyles [e.g. nomadic group predators, species which forage at extreme (>60 °C) temperatures] may have been selected for faster running speeds.
5. Although ants have a similar scaling exponent to mammals for the running speed allometry, they run slower than predicted compared with a hypothetical mammal of similar size. This may in part reflect physiological differences between invertebrates and vertebrates.     

Thermal responses and temperature tolerance of a dessert ant-lion larva

1. 1.Cueta trivirgata larvae construct pits in the dry Kuiseb River bed in the Namib Desert.

2. 2.An art, Ocymyrmex robustior comprises 65.4% of the biomass of prey consumed by the ant-lions.

3. 3.O. robustior is active between surface temperatures of 27–68°C.

4. 4.Ant-lions tolerate high body temperatures (LD₅₀ = 53.4°C).

5. 5.By exploiting the pit microclimate and by digging below the surface during extreme thermal loads, ant-lions can capture prey at surface temperatures of 13–63°C.

6. 6.These behavioural and physiological adaptations enable ant-lions to maximize the duration of vigilance and hence prey capture success.

Chemical basis of nest-mate discrimination in the ant Formica exsecta.

Distinguishing nest-mates from non-nest-mates underlies key animal behaviours, such as territoriality, altruism and the evolution of sociality. Despite its importance, there is very little empirical support for such a mechanism in nature. Here we provide data that the nest-mate recognition mechanism in an ant is based on a colony-specific Z9-alkene signature, proving that surface chemicals are indeed used in ant nest-mate recognition as was suggested 100 years ago. We investigated the cuticular hydrocarbon profiles of 10 Formica exsecta colonies that are composed almost entirely of a Z9-alkene and alkane component. Then we showed that worker aggression is only elicited by the Z9-alkene part. This was confirmed using synthetic Z9-alkene and alkane blends matched to the individual colony profiles of the two most different chemical colonies. In both colonies, only glass beads with 'nest-mate' alkene profiles received reduced aggression. Finally, changing the abundance of a single Z9-alkene on live ants was shown to significantly increase the aggression they received from nest-mates in all five colonies tested. Our data suggest that nest-mate discrimination in the social insects has evolved to rely upon highly sensitive responses to relatively few compounds.