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The soil is a heterogeneous habitat with layers that differ in many aspects. Soil animals’ morphological adaptations relate to specific microhabitat. We compared cuticle surface structures and ultrastructure of Balloniscus glaber (endogeic) and Atlantoscia floridana (epigeic) using microscopy techniques to understand how morphological characteristics allow sympatry. Species differed in scale and sensillum type and disposition, as well as cuticle thickness and layer proportion. Balloniscus glaber has curved scales and robust, caudally oriented sensilla that are most likely adaptive features for endogeic lifestyle. Its cuticle has high overall thickness and numerous stacks that provide toughness compatible with clinging strategy and higher tolerance to seasonal fluctuation. Atlantoscia floridana is an epigeic species with flat scales and long perpendicular sensilla, not adapted to the soil layer. Its delicate and flexible cuticle with thinner stacks makes it an agile runner although with lower tolerance to seasonal changes. Overall, differences in surface structure are related to microhabitat selection and ecological niche, so species can occur in same location. Differences in cuticle ultrastructure relate to behavioral strategies and environmental tolerance. This way, knowledge of species’ ecology is complemented by morphological data that can help to explain habitat partition.

Procambarus clarkii is an important invasive freshwater species whose ecological plasticity allows for its establishment in different kinds of environments; such plasticity is also reflected in its diet with two main consequences: invasion success and impact on native biota. In order to investigate P. clarkii’s feeding habits, examine how its diet varies both seasonally and among different demographic groups (reproductive males, non-reproductive males and females) and explore the two consequences mentioned above, we investigated the trophic role of this species in an Atlantic Forest conservation area in the city of Sao Paulo (Brazil). A total of 540 specimens collected monthly over a year were measured and weighed. Their stomachs were weighed and classified according to the degree of stomach fullness. Stomach contents were examined, and animal and plant matter weighed. Food items were identified to the lowest possible taxonomic level and the percentage of occurrence of each item was calculated, as well as the diet diversity. Collected data were compared according to seasons and demographic groups through the Analysis of Similarity and Similarity Percentage Analysis. The percentage of animal weight attributed to stomach weight and the degree of fullness of stomachs did not vary significantly among seasons; however, non-reproductive males had significantly less full stomachs. Diet composition was evenly balanced between plant and animal material for both reproductive males and females, while non-reproductive males consumed a lower proportion of animal matter. The diversity in diet composition was high in all seasons and for all demographic groups, although always slightly lower for non-reproductive males. The percentage of occurrence of food items evidenced high consumption of algae and macrophytes throughout the year. It also reflected the seasonal variation of consumed prey, with a shift in consumption of insects and microcrustaceans in spring and summer to decapods and amphibians in fall and winter. The dissimilarity in diet composition was more pronounced among demographic groups than among seasons, being non-reproductive males the most different, with higher ingesting of less evasive prey. Nonetheless, winter differed from other seasons and was the season with least different food composition among demographic groups, indicating a homogenization in diet composition, which might be due to restricted availability of resources. Procambarus clarkii at Jaragua State Park demonstrated conspicuous dietary variability and flexibility. The occurrence of filled stomachs indicates that food resources are not a constriction for this population. The species presented a diversified and adaptable diet, foraging on algae and macrophytes, and preying on different vertebrate and invertebrate taxa. Its trophic plasticity favors successful establishment in invaded areas and summed to its notable voracity, P. clarkii offers a wide, variable and significant interaction in food webs, being able to generate major impacts on native species by its feeding habits.

For many animal species, there is a relationship between life history strategies, as predicted by the r – K -selection theory, degree of habitat specialization and response to habitat alteration and loss. Here we compare two sympatric woodlice species with contrasting patterns of habitat use and geographical distribution. We predict that Atlantoscia floridana (Philosciidae), considered a habitat generalist, would exhibit the r -selected traits, whereas Balloniscus glaber (Balloniscidae), considered a habitat specialist, should have the K -selected traits. We analyzed several life history traits as well as life and fecundity tables using 715 and 842 females of A. floridana and B. glaber , respectively, from populations living in syntopy in southern Brazil. As predicted, most evaluated traits allow A. floridana to be considered an r -strategist and B. glaber a K -strategist: A. floridana showed a shorter lifetime, faster development, earlier reproduction, a smaller parental investment, higher net reproductive rate ( R 0 ), a higher growth rate ( r ) and a shorter generation time ( T ) in comparison to B. glaber . A. floridana seems to be a successful colonizer with a high reproductive output. These characteristics explain its local abundance, commonness and wide geographical distribution. On the contrary, B. glaber has a restricted geographical distribution that is mainly associated with Atlantic forest fragments, a biome threatened by deforestation and replacement by monocultures. Its narrow distribution combined with the K -selected traits may confer to this species an increased extinction risk.

Data were obtained on the population structure and reproduction of Atlantoscia floridana, one of the most common species of terrestrial isopods in the restinga (coastal dune) forests of the state of Rio Grande do Sul, southern Brazil. During a 19-month period, a total of 7833 individuals were sampled: 2792 males, 3400 females and 1691 mancas. There was a significant difference between the size of both males and females collected in 2000 and 2001: the mean size was smaller in the second year when individuals in the larger size classes were lacking. Population density varied with season. The minimum population was 131 ind per m2 individuals, the maximum 1040 ind per m2 and the mean 450 per m2. While the overall sex ratio was clearly female biased, the operational sex ratio favored males, and showed no changes with season. Because both ovigerous and post-ovigerous females were present throughout the year, reproduction is considered continuous; however, reproduction peaked during autumn and spring. Ovigerous females were measured (CW = cephalothorax width) and the number of eggs was counted. Fecundity (F) varied from 5 to 23 eggs ( x ¯ = 11.18 ± 4) per female, and was expressed by the regression F = –18.48 + 22.59 CW, with the female cephalothorax width varying from 1.04 to 1.68 mm. Marsupial mortality was only 0.9%. Egg production was 588 eggs per m2 in spring and 660 eggs per m2 in autumn. Recruitment occurred in all months, and eggs, embryos and marsupial mancas were also present year-round. A. floridana is the dominant species of terrestrial isopod in the study area. Its most remarkable characteristic is its high reproductive investment.

The diversity of Oniscidea across a 1000-m altitudinal gradient comprising three distinct environments—the coastal plain, the highland slopes, and the highlands—was described and analysed. We employed 1 h-long exploratory manual sampling at 41 sites. Fourteen species were identified, of 818 individuals collected. Sampling-effort curves stabilised for all three environments; analytical estimates of species richness did not exceed the observed value. Abundance did not vary significantly among environments, and local species richness differed only marginally. However, the Shannon diversity index for local sites indicated highland slopes to be significantly more diverse than the coastal region; the same was true for bootstrap estimates at the regional level. Two species appeared in all three environments, comprising 72.7% of the abundance. The coastal region and highlands had one exclusive species each, and the highland slopes had three. The first two environments are more similar to each other than to the slopes, although they are not contiguous. The altitudinal gradient of diversity was hump-shaped, because the highland slopes were most diverse. The reasons for this pattern are not biogeographical; that is, the highland slopes are not a contact zone between the highlands and the coast. A complete explanation depends upon better understanding of the effect of soil type and terrain slope on the diversity of terrestrial isopods. © 2005 Elsevier SAS. All rights reserved.