Artificial light at night causes community instability of bacterial community in urban soils.

Urban soils host diverse bacteria crucial for ecosystem functions and urban health. As urbanization rises, artificial light at night (ALAN) imposes disturbances on soil ecosystems, yet how ALAN affects the structure and stability of soil bacterial community remains unclear. Here we coupled a short-term incubation experiment, community profiling, network analysis, and in situ field survey to assess the ecological impacts of ALAN. We showed that ALAN influenced bacterial compositions and shifted the bacterial network to a less stable phase, altering denitrification potential. Such transition in community stability probably resulted from an ALAN-induced decrease in competition and/or an increase in facilitation, in line with the Stress Gradient Hypothesis. Similar destabilizing effects were also detected in bacterial networks in multiple urban soils subjected to different levels of ALAN stress, supporting the action of ALAN on naturally-occurring soil bacterial communities. Overall, our findings highlight ALAN as a new form of anthropogenic stress that jeopardizes the stability of soil bacterial community, which would facilitate ecological projection of expanding ALAN exposure.

Trophic downgrading decreases species asynchrony and community stability regardless of climate warming.

Theory and some evidence suggest that biodiversity promotes stability. However, evidence of how trophic interactions and environmental changes modulate this relationship in multitrophic communities is lacking. Given the current scenario of biodiversity loss and climate changes, where top predators are disproportionately more affected, filling these knowledge gaps is crucial. We simulated climate warming and top predator loss in natural microcosms to investigate their direct and indirect effects on temporal stability of microbial communities and the role of underlying stabilising mechanisms. Community stability was insensitive to warming, but indirectly decreased due to top predator loss via increased mesopredator abundance and consequent reduction of species asynchrony and species stability. The magnitude of destabilising effects differed among trophic levels, being disproportionally higher at lower trophic levels (e.g. producers). Our study unravels major patterns and causal mechanisms by which trophic downgrading destabilises large food webs, regardless of climate warming scenarios.

Tree diversity effects through a temporal lens: Implications for the abundance, diversity and stability of foraging birds.

Tree diversity exerts a strong influence on consumer communities, but most work has involved single time point measurements over short time periods. Describing temporal variation associated with diversity effects over longer time periods is necessary to fully understand the effects of tree diversity on ecological function. We conducted a year-long study in an experimental system in southern Mexico assessing the effects of tree diversity on the abundance and diversity of foraging birds. To this end, we recorded bird visitation patterns in 32 tree plots (21 × 21 m; 12 tree species monocultures, 20 four-species polycultures) every 45 days (n = 8 surveys) and for each plot estimated bird abundance, richness, functional diversity (FD) and phylogenetic diversity (PD). In each case, we reported temporal (intra-annual) variation in the magnitude of tree diversity effects, and calculated the temporal stability of these bird responses. Across surveys, tree diversity noticeably affected bird responses, demonstrated by significantly higher abundance (43%), richness (32%), PD (25%) and FD (25%) of birds visiting polyculture plots compared to monoculture plots, as well as a distinct species composition between plot types. We also found intra-annual variation in tree diversity effects on these response variables, ranging from surveys for which the diversity effect was not significant to surveys where a significant 80% increase (e.g. for bird FD and PD) was observed in polyculture relative to monoculture plots. Notably, tree diversity increased the stability of all bird responses, with polycultures having a greater stability abundance (18%), richness (38%), PD (32%), and FD (35%) of birds visiting tree species polycultures compared to monocultures. These results show that tree diversity not only increases bird visitation to plots, but also stabilizes bird habitat usage over time in ways that could implicate insurance-related mechanisms. Such findings are highly relevant for understanding the long-term effects of plant diversity on vertebrates and the persistence of bird-related ecosystem functions. More work is needed to unveil the ecological mechanisms behind temporal variation in vertebrate responses to tree diversity and their consequences for community structure and function.

Temporal changes in hamlet communities (Hypoplectrus spp., Serranidae) over 17 years.

Transect surveys of hamlet communities (Hypoplectrus spp., Serranidae) covering 14 000 m2 across 16 reefs off La Parguera, Puerto Rico, are presented and compared with a previous survey conducted in the year 2000. The hamlet community has noticeably changed over 17 years, with a > 30% increase in relative abundance of the yellowtail hamlet Hypoplectrus chlorurus on the inner reefs at the expense of the other hamlet species. The data also suggest that the density of H. chlorurus has declined and that its distribution has shifted towards shallower depths. Considering that H. chlorurus has been previously identified as one of the few fish showing a positive association with seawater turbidity on the inner reefs of La Parguera and that sedimentation of terrestrial origin has increased over recent decades on these reefs, it is proposed that turbidity may constitute an important but so far overlooked ecological driver of hamlet communities.

Pleistocene megafaunal interaction networks became more vulnerable after human arrival.

The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics, which may favour extinction cascades in communities facing extrinsic perturbations. Our findings suggest that the basic aspects of the organization of ecological communities may have played an important role in major extinction events in the past. Knowledge of community-level properties and their consequences to dynamics may be critical to understand past and future extinctions.

The effects of press and pulse disturbance by long and short-term pollution on the fish community in the Sinos River, RS, Brazil / Efeitos de distúrbios contínuos e pulsados da poluição aguda e de longo prazo sobre a comunidade de peixes no Rio dos Sinos, RS, Brasil

The fish fauna of the Sinos River has been subjected to severe pollution since the 1970´s. Continuous discharges of industrial and municipal sewage cause hypoxia and often even fish kills. The objectives of the present study are to assess long-term effects of pollution on the fish community over a time scale of approximately ten years and to investigate recuperation of the fish fauna after a massive fish kill in 2006. To assess the long-term impacts, seasonal sampling was conducted from September 2007 to March 2009 in four sites which were investigated in 1998/99 with the same methodology. The effects of the fish kill were investigated by comparing the present fauna in the affected river stretch with the fauna of an unaffected adjacent river stretch. The collective community properties richness and Shannon diversity changed during the ten year interval in a consistent pattern. Richness and Shannon diversity increased significantly in all sites, abundance values, however, did not. Analysis of species constancy and cluster analysis showed that the differences between the 1998/99 and 2007/09 studies were relatively small. The comparison of the reaches affected by the 2006 fish kills showed a rapid recovery within one year. Probably the Sinos fish fauna suffered the most severe impacts in the 70s of the last century, which could not be documented by this study. After an initial decline, the community displays relatively stable patterns with a tendency of recovery. After a severe fish kill, faunal recovery was rapid, probably favoured by the proximity of unpolluted source areas and physical habitat integrity of the Sinos River.

A fauna de peixes do Rio dos Sinos vem sendo exposta a uma poluição grave desde os anos 70 do século passado. Descargas contínuas de esgotos industriais e urbanos causaram hipóxia e recorrentes mortandades de peixes. Os objetivos do presente estudo são: avaliar os efeitos de longo prazo da poluição sobre a comunidade de peixes e investigar a recuperação da ictiofauna após uma mortandade severa em 2006. Para avaliar os impactos de longo prazo, foram realizados amostragens sazonais entre setembro de 2007 a março de 2009 em quatro locais que foram investigados em 1998/99 com a mesma metodologia. Os efeitos da mortandade de peixes foram investigados comparando a fauna no trecho afetado pela mortandade com o que não foi afetado. As propriedades coletivas da comunidade íctica riqueza e diversidade de Shannon aumentaram durante o intervalo de 10 anos em todos os pontos de amostragem, porém os valores da abundância ficaram estáveis. A análise da constância das espécies e a análise de agrupamento mostraram que as diferenças encontradas entre os estudos 1998-1999 e 2007/09 são pouco expressivas. A comparação dos trechos afetados e não afetados pela mortandade de peixes mostrou uma rápida recuperação da fauna que ocorreu em um ano. A ictiofauna do Rio dos Sinos sofreu provavelmente os impactos mais graves nos anos 70 do século passado, contudo, não documentado por este estudo. Depois de um declínio inicial a comunidade exibiu padrões relativamente estáveis com tendências de recuperação. Após as mortandades de 2006 a recuperação da fauna foi rápida, provavelmente favorecida pela proximidade de áreas de fonte não poluídas e pela integridade física dos habitats do Rio dos Sinos.

The effects of press and pulse disturbance by long and short-term pollution on the fish community in the Sinos River, RS, Brazil

p>The fish fauna of the Sinos River has been subjected to severe pollution since the 1970´s. Continuous discharges of industrial and municipal sewage cause hypoxia and often even fish kills. The objectives of the present study are to assess long-term effects of pollution on the fish community over a time scale of approximately ten years and to investigate recuperation of the fish fauna after a massive fish kill in 2006. To assess the long-term impacts, seasonal sampling was conducted from September 2007 to March 2009 in four sites which were investigated in 1998/99 with the same methodology. The effects of the fish kill were investigated by comparing the present fauna in the affected river stretch with the fauna of an unaffected adjacent river stretch. The collective community properties richness and Shannon diversity changed during the ten year interval in a consistent pattern. Richness and Shannon diversity increased significantly in all sites, abundance values, however, did not. Analysis of species constancy and cluster analysis showed that the differences between the 1998/99 and 2007/09 studies were relatively small. The comparison of the reaches affected by the 2006 fish kills showed a rapid recovery within one year. Probably the Sinos fish fauna suffered the most severe impacts in the 70s of the last century, which could not be documented by this study. After an initial decline, the community displays relatively stable patterns with a tendency of recovery. After a severe fish kill, faunal recovery was rapid, probably favoured by the proximity of unpolluted source areas and physical habitat integrity of the Sinos River. /p>

p>A fauna de peixes do Rio dos Sinos vem sendo exposta a uma poluição grave desde os anos 70 do século passado. Descargas contínuas de esgotos industriais e urbanos causaram hipóxia e recorrentes mortandades de peixes. Os objetivos do presente estudo são: avaliar os efeitos de longo prazo da poluição sobre a comunidade de peixes e investigar a recuperação da ictiofauna após uma mortandade severa em 2006. Para avaliar os impactos de longo prazo, foram realizados amostragens sazonais entre setembro de 2007 a março de 2009 em quatro locais que foram investigados em 1998/99 com a mesma metodologia. Os efeitos da mortandade de peixes foram investigados comparando a fauna no trecho afetado pela mortandade com o que não foi afetado. As propriedades coletivas da comunidade íctica riqueza e diversidade de Shannon aumentaram durante o intervalo de 10 anos em todos os pontos de amostragem, porém os valores da abundância ficaram estáveis. A análise da constância das espécies e a análise de agrupamento mostraram que as diferenças encontradas entre os estudos 1998-1999 e 2007/09 são pouco expressivas. A comparação dos trechos afetados e não afetados pela mortandade de peixes mostrou uma rápida recuperação da fauna que ocorreu em um ano. A ictiofauna do Rio dos Sinos sofreu provavelmente os impactos mais graves nos anos 70 do século passado, contudo, não documentado por este estudo. Depois de um declínio inicial a comunidade exibiu padrões relativamente estáveis com tendências de recuperação. Após as mortandades de 2006 a recuperação da fauna foi rápida, provavelmente favorecida pela proximidade de áreas de fonte não poluídas e pela integridade física dos habitats do Rio dos Sinos. /p>

The effects of press and pulse disturbance by long and short-term pollution on the fish community in the Sinos River, RS, Brazil / Efeitos de distúrbios contínuos e pulsados da poluição aguda e de longo prazo sobre a comunidade de peixes no Rio dos Sinos, RS, Brasil

The fish fauna of the Sinos River has been subjected to severe pollution since the 1970´s. Continuous discharges of industrial and municipal sewage cause hypoxia and often even fish kills. The objectives of the present study are to assess long-term effects of pollution on the fish community over a time scale of approximately ten years and to investigate recuperation of the fish fauna after a massive fish kill in 2006. To assess the long-term impacts, seasonal sampling was conducted from September 2007 to March 2009 in four sites which were investigated in 1998/99 with the same methodology. The effects of the fish kill were investigated by comparing the present fauna in the affected river stretch with the fauna of an unaffected adjacent river stretch. The collective community properties richness and Shannon diversity changed during the ten year interval in a consistent pattern. Richness and Shannon diversity increased significantly in all sites, abundance values, however, did not. Analysis of species constancy and cluster analysis showed that the differences between the 1998/99 and 2007/09 studies were relatively small. The comparison of the reaches affected by the 2006 fish kills showed a rapid recovery within one year. Probably the Sinos fish fauna suffered the most severe impacts in the 70s of the last century, which could not be documented by this study. After an initial decline, the community displays relatively stable patterns with a tendency of recovery. After a severe fish kill, faunal recovery was rapid, probably favoured by the proximity of unpolluted source areas and physical habitat integrity of the Sinos River.(AU)

A fauna de peixes do Rio dos Sinos vem sendo exposta a uma poluição grave desde os anos 70 do século passado. Descargas contínuas de esgotos industriais e urbanos causaram hipóxia e recorrentes mortandades de peixes. Os objetivos do presente estudo são: avaliar os efeitos de longo prazo da poluição sobre a comunidade de peixes e investigar a recuperação da ictiofauna após uma mortandade severa em 2006. Para avaliar os impactos de longo prazo, foram realizados amostragens sazonais entre setembro de 2007 a março de 2009 em quatro locais que foram investigados em 1998/99 com a mesma metodologia. Os efeitos da mortandade de peixes foram investigados comparando a fauna no trecho afetado pela mortandade com o que não foi afetado. As propriedades coletivas da comunidade íctica riqueza e diversidade de Shannon aumentaram durante o intervalo de 10 anos em todos os pontos de amostragem, porém os valores da abundância ficaram estáveis. A análise da constância das espécies e a análise de agrupamento mostraram que as diferenças encontradas entre os estudos 1998-1999 e 2007/09 são pouco expressivas. A comparação dos trechos afetados e não afetados pela mortandade de peixes mostrou uma rápida recuperação da fauna que ocorreu em um ano. A ictiofauna do Rio dos Sinos sofreu provavelmente os impactos mais graves nos anos 70 do século passado, contudo, não documentado por este estudo. Depois de um declínio inicial a comunidade exibiu padrões relativamente estáveis com tendências de recuperação. Após as mortandades de 2006 a recuperação da fauna foi rápida, provavelmente favorecida pela proximidade de áreas de fonte não poluídas e pela integridade física dos habitats do Rio dos Sinos.(AU)