Urban ecology, stakeholders and the future of ecology.

The world human population is more and more urban and cities have a strong impact on the biosphere. This explains the development of urban ecology. In this context, the goal of our work is fourfold: to describe the diversity of scientific questions in urban ecology, show how these questions are organized, to assess how these questions can be built in close interactions with stakeholders, to better understand the role urban ecology can play within ecological sciences. A workshop with scientists from all relevant fields (from ecology to sociology) and stakeholders was organized by the Foundation for Research on Biodiversity (FRB). Three types of scientific issues were outlined about (1) the biodiversity of organisms living in urban areas, (2) the functioning of urban organisms and ecosystems, (3) interactions between human societies and urban ecological systems. For all types of issues we outlined it was possible to distinguish both fundamental and applied scientific questions. This allowed building a unique research agenda encompassing all possible types of scientific issues in urban ecology. As all types of ecological and evolutionary questions can be asked in urban areas, urban ecology will likely be more and more influential in the development of ecology. Taken together, the future of towns, their biodiversity and the life of city dwellers is at stake. Increasing the space for ecosystems and biodiversity within towns is more and more viewed as crucial for the well-being of town dwellers. Depending on research and the way its results are taken into account, very different towns could emerge. Urban areas can be viewed as a test and a laboratory for the future of the interactions between human and ecological systems.

Differences in collembola species assemblages (Arthropoda) between spoil tips and surrounding environments are dependent on vegetation development.

Spoil tip production is one of the most extreme means of soil destruction, replacing the native soil with a coarse substrate. In this paper, we aim to determine the colonization of soil biota in new substrates, using collembola assemblages as an indicator. In Northern France, we sampled collembola communities in 11 coal mine spoil tips and their surroundings divided in four stages of vegetation development: bare soil, meadow, shrub and tree covers. We demonstrated that collembola assemblages of spoil tips were different from those observed in the surrounding native soil. Collembola communities on bare soil were characterized by pioneer (based on the Indval index) or exotic species (new in Northern France). However, homogenization occurred with development of vegetation cover. Indeed, our data showed no difference in springtail diversity between spoil tips and their corresponding environments regarding the tree vegetation cover. Using the Indval method, we defined pioneer, colonizing, opportunist or stenoecious species as a function of substrate affinities. Using the same method, we defined specialists, elective, preferring or indifferent species as a function of vegetation cover affinities, showing similarities with previously published surveys. Hence, our results were obtained by a focused analysis of species and their particularity. Finally, we discussed the interest in and the complementarity between the species analysis approach and the methodology dealing with functional traits and of its importance in the decision process of restoration and/or conservation of nature.

Evidence of self-organization in a gregarious land-dwelling crustacean (Isopoda: Oniscidea).

How individuals modulate their behavior according to social context is a major issue in the understanding of group initiation, group stability and the distribution of individuals. Herein, we investigated the mechanisms of aggregation behavior in Porcellio scaber, a terrestrial isopod member of the Oniscidea, a unique and common group of terrestrial crustaceans. We performed binary choice tests using shelters with a wide range of population densities (from 10 to 150 individuals). First, the observed collective choices of shelters strengthen the demonstration of a social inter-attraction in terrestrial isopods; especially, in less than 10 min, the aggregation reaches its maximal value, and in less than 100 s, the collective choice is made, i.e., one shelter is selected. In addition, the distribution of individuals shows the existence of (1) quorum rules, by which an aggregate cannot emerge under a threshold value of individuals, and (2) a maximum population size, which leads to a splitting of the populations. These collective results are in agreement with the individual's probability of joining and leaving an aggregate attesting to a greater attractiveness of the group to migrants and greater retention of conspecifics with group size. In this respect, we show that the emergence of aggregation in terrestrial isopods is based on amplification mechanisms. And lastly, our results indicate how local cues about the spatial organization of individuals may favor this emergence and how individuals spatiotemporally reorganize toward a compact form reducing the exchange with the environment. This study provides the first evidence of self-organization in a gregarious crustacean, similar as has been widely emphasized in gregarious insects and eusocial insects.

Regulatory mechanisms of group distributions in a gregarious arthropod.

In a patchy environment, how social animals manage conspecific and environmental cues in their choice of habitat is a leading issue for understanding their spatial distribution and their exploitation of resources. Here, we experimentally tested the effects of environmental heterogeneities (artificial shelters) and some of their characteristics (size and fragmentation) on the aggregation process of a common species of terrestrial isopod (Crustacea). One hundred individuals were introduced into three different heterogeneous set-ups and in a homogeneous set-up. In the four set-ups, the populations split into two aggregates: one large (approx. 70 individuals) and one smaller (approx. 20 individuals). These aggregates were not randomly distributed in the arena but were formed diametrically opposite from one another. The similarity of the results among the four set-ups shows that under experimental conditions, the environmental heterogeneities have a low impact on the aggregation dynamics and spatial patterns of the isopod, merely serving to increase the probability of nucleation of the larger aggregation at these points. By contrast, the regulation of aggregate sizes and the regular distribution of groups are signatures of local amplification processes, in agreement with the short-range activator and long-range inhibitor model (scale-dependent feedbacks). In other words, we show how small-scale interactions may govern large-scale spatial patterns. This experimental illustration of spatial self-organization is an important step towards comprehension of the complex game of competition among groups in social species.

Body shape in terrestrial isopods: A morphological mechanism to resist desiccation?

Woodlice are fully terrestrial crustaceans and are known to be sensitive to water loss. Their half-ellipsoidal shapes represent simple models in which to investigate theoretical assumptions about organism morphology and rates of exchange with the environment. We examine the influence of surface area and mass on the desiccation rates in three eco-morphologically different species of woodlice: Oniscus asellus, Porcellio scaber, and Armadillidium vulgare. Our analysis indicates that the rate of water loss of an individual depends on both the initial weight and the body surface area. Interspecific and intraspecific analyses show that the mass-specific water loss rate of a species decreases along with the ratio of surface area to volume. In particular, we show that body shape explains the difference in mass-specific water loss rates between A. vulgare and P. scaber. This observation also explains several known ecological patterns, for example, the distribution and survivorship of individuals. However, in addition to body size and shape, water loss in terrestrial isopods depends also on the coefficient of permeability (i.e., a measure of water loss rate per surface unit), which is high in O. asellus and lower (and at similar levels) in P. scaber and A. vulgare. We discuss morphological, physiological, and behavioral aspects of water loss avoidance in terrestrial isopods.

Experimental study of Lucilia sericata (Diptera Calliphoridae) larval development on rat cadavers: Effects of climate and chemical contamination.

Household products such as bleach, gasoline or hydrochloric acid have been used to mask the presence of a cadaver or to prevent the colonization of insects. These types of chemicals affect insect development and alter the forensic entomology analysis. This study was designed to test the effects of six household products (bleach, mosquito repellent, perfume, caustic soda, insecticide and unleaded gasoline) on blowfly (Lucilia sericata, Diptera: Calliphoridae) larval development. Furthermore, the effects of climate (rain or dry conditions) on larval development were analyzed. For each replication, 100 first instars were placed on a rat cadaver on which one household product was spilled. We observed a decrease in the survival rates of the larvae but no significant effect on their development times or the adult size. The same trends were observed under rainy conditions. However, the rain altered the effects of some tested household products, especially gasoline. These results demonstrate for the first time the successful development of necrophagous larvae on chemically contaminated cadavers, and provide evidence for the range of possible effects to expect.

Do necrophagous blowflies (Diptera: Calliphoridae) lay their eggs in wounds?: Experimental data and implications for forensic entomology.

This study was designed to examine the common belief that necrophagous blowflies lay their eggs in wounds. The egg-laying behaviour of Lucilia sericata was observed under controlled conditions on wet, artificially wounded or short-haired areas of rat cadavers. Flies laid significantly more eggs on the wet area and the area with short hair than on the dry area or area with long hair. No eggs were observed inside the wounds in any of the replicates. The effect of egg immersion (body fluids often exudes in wounds) on the survival rate of larvae was also investigated. In low water condition, an average of 72.7±7.9% of the larvae survived and they reached a mean length of 7.5±0.6mm. In contrast, submerging eggs under a high volume of water strongly affected their survival rate (25±3.7%) and development. Similar results were observed using unfrozen pig blood instead of water. These data question the information found in the literature regarding the preferential egg-laying behaviour of Calliphorids flies in wounds.

In vitro effects of household products on Calliphoridae larvae development: implication for forensic entomology.

Several parameters can delay the first arrival of flies on a corpse and the subsequent development of the larvae. This study focuses on the development of Lucilia sericata (Diptera: Calliphoridae) (Meigen, 1826) on household chemical-contaminated substrates. bleach, perfume, hydrochloric acid, caustic soda, insecticide, mosquito repellent, and gasoline in quantities consistent with an amount that could possibly be spilled on a corpse were mixed with beef liver to simulate contaminated fleshes. Larvae were bred at 25 °C on these media until emergence. Four developmental parameters were followed: survival rates, development times, sex ratios, and adult sizes. Hydrochloric acid, insecticide, and gasoline killed all larvae. In low quantities, caustic soda and mosquito repellent increased the development time and decreased the adult size. However, high quantities of these chemicals killed all larvae. Lastly, bleach and perfume did not affect the survival rate and barely impacted the development time or adult size. These results demonstrate common household products spilled on a corpse can strongly affect the development of Calliphoridae larvae. The effects of such products should be considered in forensic entomology cases.

The differential response of workers and queens of the ant Lasius niger to an environment marked by workers: ants dislike the unknown.

It is well known that ants can use cuticular hydrocarbons (CHCs) as a specific recognition cue. Most previous studies addressed the perception of CHCs occurring on the cuticle. However, the presence of CHCs in the environment (e.g., on the substrate) and the role of these compounds as a signal cue are less clear. In this study of the ant L. niger, CHCs were extracted from corpses of workers, from the legs of workers and from filter paper marked by workers. Behavioural choice tests were then performed to study the reactions of workers and queens to CHC passively deposited on the substrate by walking workers. A GC-MS analysis of the CHCs revealed a complex mixture of 28 peaks composed of linear alkanes, alkenes and mono-, di- or trimethylalkane. This mixture was consistently present in the three sources tested (corpses of workers, the tarsus of workers and paper marked by walking workers). Nevertheless, discriminant analyses distinguished clearly among the three types of profiles. The results of our behavioural experiments showed that the workers were able to distinguish between marked and unmarked papers but that they exhibited no preferences for different types of marked papers (papers marked by workers from their own colony or papers marked by workers from a different colony). In queens, the perception of marked papers depended on age or physiological state. Just-mated queens did not discriminate between unmarked papers and papers marked by an alien colony. In contrast, the egg-laying queens 3 days after mating significantly favoured the marked papers. We discuss the ecological relevance of the differences in decision-making between castes.

Aggregation in woodlice: social interaction and density effects.

Terrestrial isopods are known to be sensitive to humidity, brightness or temperature. Until now, aggregation was assumed to depend on these sensitivities as a result of individual preferences. In this paper, we show that the social component is also important in the isopod aggregation phenomenon. In experimental arenas with two identical shelters up to nearly 90% of woodlice aggregated under shelters. This aggregation was quick as in 10 minutes most of the animals aggregated, irrespective of their density. Nonetheless, 10-15% of the animals walked around the arena, rarely forming very small and short-lasting aggregates outside shelters. Woodlice aggregated preferably under one of the shelters in 77% of experiments. Indeed, almost 80% of the animals out of 40, 60 or 80 animals in the arena aggregated under one shelter. In arenas with 100 individuals the aggregations were proportionally smaller (70%). Our results revealed that 70 animals was a maximum number of woodlice in an aggregate. We concluded that the location of aggregates is strongly governed by individual preferences but the dynamics of aggregation and collective choice are controlled by social interaction between congeners. The tested densities of the animals in the arena did not impact the aggregation patterns.

Individual preferences and social interactions determine the aggregation of woodlice.

BACKGROUND: The aggregation of woodlice in dark and moist places is considered an adaptation to land life and most studies are focused on its functionality or on the behavioural mechanisms related to the individual's response to abiotic factors. Until now, no clear experimental demonstration was available about aggregation resulting from inter-attraction between conspecifics. METHODOLOGY/MAIN FINDINGS: We present the dynamics of aggregation, not previously described in detail in literature, as being independent of the experimental conditions: homogeneous and heterogeneous environments with identical or different shelters. Indeed whatever these conditions, the aggregation is very quick. In less than 10 minutes more than 50% of woodlice were aggregated in several small groups in the homogeneous environment or under shelters in the heterogeneous environment. After this fast aggregation, woodlice progressively moved into a single aggregate or under one shelter. CONCLUSIONS/SIGNIFICANCE: Here we show for the first time that aggregation in woodlice implies a strong social component and results from a trade-off between individual preferences and inter-attraction between individuals. Moreover, our results reveal that the response to the heterogeneities affects only the location of the aggregates and not the level of aggregation, and demonstrate the strong inter-attraction between conspecifics which can outweigh individual preferences. This inter-attraction can lead to situations that could seem sub-optimal.