Temporal fluctuations and experimental effects in desert plant communities

In the Chihuahuan Desert of the southwestern United States we monitored responses of both winter and summer annual plant communities to natural environmental variation and to experimental removal of seed-eating rodents and ants for 13 years. Analyses of data on population densities of the species by principal component analysis (PCA) followed by repeated measures analysis of variance (rmANOVA) on PCA scores showed that: (1) composition of both winter and summer annual communities varied substantially from year to year, presumably in response to interannual climatic variation, and (2) community composition of winter annuals was also significantly affected by the experimental manipulations of seed-eating animals, but the composition of the summer annual community showed no significant response to these experimental treatments. Canonical discriminant analysis (CDA) was then applied to the data for winter annuals to more clearly identify the responses to the different classes of experimental manipulations. This analysis showed that removing rodents or ants or both taxa caused distinctive changes in species composition. There was a tendency for large-seeded species to increase on rodent removal plots and to decrease on ant removal plots, and for small-seeded species to change in the opposite direction. In the winter annual community there was a significant time x treatment interaction: certain combinations of species that responded differently to removal of granivores also showed opposite fluctuations in response to long-term climatic variation. The large year-to-year variation in the summer annual community was closely and positively correlated across all experimental treatments. The use of multivariate analysis in conjunction with long-term monitoring and experimental manipulation shows how biotic interactions interact with variation in abiotic conditions to affect community dynamics.     

Ciudadanía activa y personas mayores: viejos conceptos,nuevos abordajes. Una revisión sistemática y metasíntesis cualitativa

The politics of active ageing present active citizenship of the elderly as a key challenge for the coming years. Active citizenship has been defined in different ways (as complimentary in most cases), outlining an eclecticism of participatory activities that includes political engagement in a participatory and deliberative manner, as well as community and voluntary action. This term is found in different contexts such as formal politics, work, civil society, and the home. This paper, based on a systematic review, identifies the context in which this concept emerges in relation to older people and people with dementia. It also analyses the different expressions of active citizenship used, and provides key elements to be taken into account in the formulation of policies in a context of accelerated demographic ageing and where dementia is a public health priority. The notion of active citizenship in old age is a step forward from active ageing to a broader concept that integrates the principle of equality between people irrespective of gender, age and the need for support.     

Palaeocommunity Dynamics and Behavioral Analysis of Conichnus: Bhuj Formation (Lower Cretaceous),Kachchh-India

A palaeocommunity of large Conichnus conicus, a conical, cone-in-cone shaped burrow, created by sea anemones, occurs in medium-grained, crossbedded, well-sorted sandstone in the middle part of the Cretaceous Guneri Member of the Bhuj Formation in India. The trace fossil Conichnus is considered to be a common element of the Skolithos ichnofacies and is interpreted to reflect equilibrium movement in response to substrate aggradation. In the present study, three different varieties of Conichnus conicus are distinguished based on morphology and internal fabric. Community dynamics and burrowing behavior are revealed by inter-burrow relationships, burrow initiation levels and sedimentology. Three types of behavior are envisaged: retrusive equilibrium, protrusive equilibrium response, and escape behavior. Palaeocommunity dynamics show that the tracemakers consisted of only adult organisms that initiated burrows during neap tides and are adapted to feed effectively during weak flow conditions. The occurrence of Conichnus palaeocommunity in the Guneri Member indicates the tidal conditions in a fully marine setting. Results presented herein may aid in the understanding of palaeocommunity dynamics in other shallow marine sequences.     

The dynamics of experimental arable weed communities under different management practices

Abstract. Weed communities, comprising 12 introduced species at constant starting densities and three species already present in the seed bank, were followed through three years of continuous winter wheat. The wheat and weeds were subjected to two treatments in a split-plot factorial design, organic contrasting with conventional fertilizer, and ploughing plus hand-roguing contrasting with minimum tillage plus herbicide. The minimum tilled plots developed in a uniform manner, and became dominated by very high densities of Anisantha sterilis. Agrostemma githago and Galium aparine also persisted in these plots at lower densities. The ploughed plots had a lower total density but a greater range of species. Stellaria media, Veronica persica and Avena fatua were the most common; other species occurred at lower densities. The major effect of fertilizer treatment was a greater initial increase by G. aparine on the organic, minimum tilled plots compared with the conventionally fertilized, minimum tilled plots. Species associated with minimum tillage were annuals with either no or a short term seed bank and autumn germination and rather predictable dynamics, whereas species that did well under ploughing were either spring germinating or had a persistent seed bank, implying greater annual variation in population size associated with weather conditions. There seemed no clear way to distinguish between those species which were abundant on the ploughed plots and those which were scarce under all conditions using readily accessible data.     

Using Stable Isotopes to Differentiate Trophic Feeding Channels within Soil Food Webs

The soil is probably the most diverse habitat there is, with organisms ranging in sizes from less than 1 μm to several metres in length. However, it is increasingly evident that we know little about the interactions occurring between these organisms, the functions that they perform as individual species, or together within their different feeding guilds. These interactions between groups of organisms and physical and chemical processes shape the soil as a habitat and influence the nature of the soil food web with consequences for the above‐ground vegetation and food web. Protists are known as one of the most abundant groups of bacterivores within the soil; however, they are also consumers of a number of other food sources. Even though they are responsible for a large proportion of the mineralisation of bacterial biomass and have a large impact on the C and N cycles within the soil they are regularly overlooked when investigating the complete soil food web. Recently, stable isotopes have been used to determine trophic interactions and here we describe how this technique has been used to highlight linkages between protists and the soil food web.     

Species richness and composition of amphibians and reptiles in a fragmented forest landscape in northeastern Bolivia

We quantified patterns of species richness and species composition of frogs and reptiles (lizards and snakes) among three habitats (continuous forest, forest islands, and a seasonally flooded savannah) and between forest island size and isolation classes in a floristic transition zone in northeastern Santa Cruz Department, Bolivia. Species richness was similar across macrohabitats, as was faunal composition of forested habitats, although savannah harbored a distinct herpetofauna. On forest islands, richness and composition of forest frogs was largely related to isolation, whereas reptiles were affected by both isolation and habitat. The observation that isolation rather than area was the primary driver of distribution patterns on forest islands stands in contrast to many studies, and may be a function of (1) the greater range in forest island isolation values compared to area or (2) the long history of isolation in this landscape.     

Geographical patterns of persistence in duck guilds

Geographical gradients of persistence in community structure have been suggested to be causally related to underlying gradients of species diversity, environmental variability and/or productivity. In order to test whether the persistence of breeding duck communities was dependent on any one of these three factors, thirty-three years of census data from the Canadian prairie and boreal forest regions was examined along geographical gradients of wetland habitat variability and productivity. For breeding ducks, locally derived patterns of persistence were generally independent of local habitat conditions. Persistence appeared to be related more to patterns of emigration and immigration in response to climatic conditions (i.e., drought) in the southern prairies than to local species richness, wetland habitat variability or productivity. It is suggested, therefore, that analyses of community persistence derived at small spatial scales may be of limited value if the structure of communities is not regulated by local conditions.     

Litter-dwelling ants as bioindicators to gauge the sustainability of small arboreal monocultures embedded in the Amazonian rainforest

One of the greatest threats to biodiversity and the sustainable functioning of ecosystems is the clearing of forests for agriculture. Because litter-dwelling ants are very good bioindicators of man-made disturbance, we used them to compare monospecific plantations of acacia trees, cocoa trees, rubber trees and pine trees with the surrounding Neotropical rainforest (in contrast to previous studies on forest fragments embedded in industrial monocultures). Although the global level of species turnover was weak, species richness decreased along a gradient from the forest (including a treefall gap) to the tree plantations among which the highest number of species was noted for the cocoa trees, which are known to be a good compromise between agriculture and conservation. Species composition was significantly different between natural habitats and the plantations that, in turn, were different from each other. Compared to the forest, alterations in the ant communities were (1) highest for the acacia and rubber trees, (2) intermediate for the cocoa trees, and, (3) surprisingly, far lower for the pine trees, likely due to very abundant litter. Functional traits only separated the rubber tree plantation from the other habitats due to the higher presence of exotic and leaf-cutting ants. This study shows that small monospecific stands are likely sustainable when embedded in the rainforest and that environmentally-friendly strategies can be planned accordingly.