Reduced Species Richness Research Articles

Directional effects of biotic homogenization of bird communities in Mexican seasonal forests

ABSTRACT Biotic homogenization—the erosion of biological differences between ecosystems owing to human perturbation—is a trait of the global biodiversity crisis that can affect tropical dry forest biodiversity. We tested whether biotic homogenization was occurring in resident forest bird communities in west-central Mexico. We conducted point-count surveys to assess biotic dissimilarity between resident bird communities in tropical deciduous and oak forests in the upper Balsas River basin across 3 levels of anthropogenic perturbation: primary forest, second-growth forest, and human settlements. We detected a reduction in species richness and taxonomic dissimilarity with increasing anthropogenic effects, due to a directional pattern in which lowland species expanded their elevational distributions up into oak forests. These results point to a need to change agricultural strategies to mitigate impacts on natural vegetation cover and biodiversity.

Insularity effects on bird immune parameters: A comparison between island and mainland populations in West Africa.

Oceanic islands share several environmental characteristics that have been shown to drive convergent evolutionary changes in island organisms. One change that is often assumed but has seldom been examined is the evolution of weaker immune systems in island species. The reduction in species richness on islands is expected to lead to a reduced parasite pressure and, given that immune function is costly, island animals should show a reduced immune response. However, alternative hypotheses exist; for example, the slower pace of life on islands could favor the reorganization of the immune system components (innate vs. acquired immunity) on islands. Thus far, few island species have been studied and no general patterns have emerged. Here, we compared two immune parameters of birds from São Tomé and Príncipe islands to those of their close relatives at similar latitudes on the mainland (Gabon, West Africa). On islands, the acquired humoral component (total immunoglobulins) was lower for most species, whereas no clear pattern was detected for the innate component (haptoglobin levels). These different responses did not seem to arise from a reorganization of the two immune components, as both total immunoglobulins and haptoglobin levels were positively associated. This work adds to the few empirical studies conducted so far which suggest that changes in immune parameters in response to insularity are not as straightforward as initially thought.

Effects of urbanization on the avian community in a southern Brazilian city

This paper compares the proportion of urban tolerant birds in the urban avian community and the amount of built-up areas, mostly impervious surface, as indicators of urbanization on patterns of bird species richness in a southern Brazilian city. From September to December 2013 (breeding season), bird surveys were conducted in 120 squares of 100 ha randomly select within Curitiba, Paraná, Brazil. All bird species seen or heard during the sample timeframe were recorded. The extent of urban modification and disturbance was estimated directly from urban landscape data analyses through a geographic information system. Linear regressions were graphed and Spearman rank correlations were calculated to assess the relationship of overall species richness and the percentage of urban tolerant birds against the percentage of built-up areas as the predictor variable. Kruskal-Wallis non-parametric analyses of variance were performed to test if the total richness or the percentage of urban tolerant birds on the assemblages differed between categories of urbanization (low, intermediate and high). We recorded 102 bird species, including 13 urban tolerant species. As expected, urbanization significantly reduced species richness, but urban tolerant species were less affected to changes on land modifications associated to urban growth. The increase in representativeness of “urban-adaptable” species on the bird assemblages of intermediate and high-urbanized areas in Curitiba was probably favored by their broad environmental tolerance. Most urban tolerant species registered are ground foraging resident birds, use a diverse array of anthropogenic resources, and can be found occupying various types of habitat in several human-modified ecosystems.

Complex plant community responses to modifications of disturbance and nutrient availability in productive permanent grasslands

AbstractQuestionDo the effects of grazing and fertilization on taxonomic and functional diversity follow the dynamic equilibrium model?LocationLong‐term permanent upland grasslands, Massif‐central, France.MethodsOver 8 yr, we monitored vegetation changes in 24 experimental plots in two productive grasslands after modification of grazing intensity (including abandonment) or fertilization regime (including cessation of fertilization). Botanical surveys and plant trait measurements (LDMC, SLA and reproductive plant height) were performed within each plot. We analysed taxonomic responses using PRC and functional responses from observed temporal changes of CWM traits and Rao index.ResultsGrazing abandonment led to significant reductions in species richness and functional convergence toward taller plants with higher LDMC in both grasslands. Intermediate and high grazing pressure did not differ but showed strong variations in taxonomic diversity between years. Changes in functional vegetation structure were mostly driven by species turnover and weakly influenced by intraspecific trait variability. Community responses to modified fertilization regime were more complex, with strong differences between the two mown grasslands. Species richness did not change significantly although species evenness decreased in the highly fertilized treatments (NPK), particularly in the most productive grassland. Here, functional changes were largely driven by intraspecific trait variability. Both functional divergence and convergence were found for different traits. In NPK, grassland assemblages converged toward taller plants while SLA diverged.ConclusionsIn our upland study system the different components of grassland diversity responded differently, in terms of direction or rate of change and mostly under extreme modifications of management. Following abandonment, the observed patterns suggest a prominent and consistent role of competitive exclusion, as expected under the DEM. However, our findings also suggest the role of additional processes, especially the importance of niche differentiation, for our mown grassland under NPK. Timing and net effects of these combined assembly drivers were sensitive to even slight differences in initial productivity and species composition.

Discordant response of spider communities to forests disturbed by deer herbivory and changes in prey availability

AbstractDespite the breadth of research on impacts of dense ungulate populations and invasive plants on native vegetation, work involving indirect effects on spider communities is explicitly lacking. Forest spiders depend on palatable insect prey and habitat structure, both of which are affected by herbivory and invasive vegetation. To examine the indirect interactions between spiders and these influential factors, we sampled spider communities, insect prey, and vegetation in paired deer exclusion plots in central Maryland. Spider abundance and richness increased with greater prey density, while increased habitat structure from deer exclusion reduced species richness and the abundance of a dominant web‐building species. Multivariate analyses of spider families also demonstrated the importance of both prey availability and structural complexity to spider community composition. This work identifies the importance of both habitat structure and insect prey in defining the composition, abundance, and richness of forest spider communities. A long history of heavy browsing pressure has resulted in local spider fauna consisting of many species that are able to thrive in low‐growing vegetation and open forest understories. Such changes to vegetative structure from dense deer populations and invasive plants have the potential to affect these important primary predators as well as araneophagic birds and the nutritional dynamics of forest food webs.

Oral treatment with Lactobacillus rhamnosus attenuates behavioural deficits and immune changes in chronic social stress

BackgroundStress-related disorders involve systemic alterations, including disruption of the intestinal microbial community. Given the putative connections between the microbiota, immunity, neural function, and behaviour, we investigated the potential for microbe-induced gut-to-brain signalling to modulate the impact of stress on host behaviour and immunoregulation.MethodsMale C57BL/6 mice treated orally over 28 days with either Lactobacillus rhamnosus (JB-1) ™ or vehicle were subjected to chronic social defeat and assessed for alterations in behaviour and immune cell phenotype. 16S rRNA sequencing and mass spectrometry were employed to analyse the faecal microbial community and metabolite profile.ResultsTreatment with JB-1 decreased stress-induced anxiety-like behaviour and prevented deficits in social interaction with conspecifics. However, JB-1 did not alter development of aggressor avoidance following social defeat.Microbial treatment attenuated stress-related activation of dendritic cells while increasing IL-10+ regulatory T cells. Furthermore, JB-1 modulated the effect of stress on faecal metabolites with neuroactive and immunomodulatory properties. Exposure to social defeat altered faecal microbial community composition and reduced species richness and diversity, none of which was prevented by JB-1.Stress-related microbiota disruptions persisted in vehicle-treated mice for 3 weeks following stressor cessation.ConclusionsThese data demonstrate that despite the complexity of the gut microbiota, exposure to a single microbial strain can protect against certain stress-induced behaviours and systemic immune alterations without preventing dysbiosis. This work supports microbe-based interventions for stress-related disorders.

How small cities affect the biodiversity of ground-dwelling mammals and the relevance of this knowledge in planning urban land expansion in terms of urban wildlife

Fundamental principles regarding urban biodiversity are based on studies conducted in large cities. However we cannot know whether the same phenomena occur in smaller cities or how small cities affect biodiversity. Small cities are an inherent element of urbanization and in the future, most global urban growth is expected to take place in small and medium-sized cities. Understanding the effects of small cities on biodiversity will be an important aspect in planning urban land expansion. Our study examined the effects of a small city on communities of small ground-dwelling mammals on 41 sites arranged in a four step gradient of urbanization. In 6700 trap-days, we caught 2333 individuals comprising 15 species. In the downtown area the same phenomena as those described for large cities were observed: a reduction in species richness and diversity, a decline in the abundance of urban sensitive species and an increase in synurbic species. However, in contrast to large city studies, green areas outside the downtown area did not differ from rural sites in small mammal population parameters. This phenomenon of relatively unchanged fauna outside the downtown area shows that small cities have the potential to maintain a high level of diversity of small ground-dwelling mammals if appropriate planning of further building expansion is implemented. More studies of small cities are needed to better assess their impact on biodiversity. This knowledge can then be applied in better planning for urban wildlife. Generalizations based solely on large city studies are inadequate and may lead to incomplete or inappropriate conservation strategies for small cities.

Urban grasslands support threatened water voles

Urbanisation is often linked with habitat loss and a reduction in species richness but some species may be able to adapt to urban environments. Water voles Arvicola amphibius, a rapidly declining species in the UK, have recently been recorded in isolated grassland habitats in Glasgow, Scotland’s largest city (human population 1.2 million). The aim of this study was to determine the distribution and habitat characteristics of water vole populations occupying these dry grasslands. Field work was undertaken from March to October 2014 in a 34 km2 study area located 3 km east of the city centre. Field sign transects recorded water vole presence in 21/65 (32%) and 19/62 (31%) surveyed sites in spring and autumn, respectively. Vole occupancy increased with distance from water and was greatest in parkland, followed by sites with rank vegetation and roadside habitats. Occupancy was lower where signs of predators were recorded but surprisingly occupancy was found to be greater in the most disturbed sites, perhaps linked to the fact that many of these sites were public parks containing suitable grassland. Sites occupied by water voles were classed as neutral grasslands with species composition dominated by two main species. The number of grassland sites occupied by water voles, especially within public areas suggests that careful management of these urban grassland habitats will benefit the conservation of this highly threatened species in the UK.

Environmental flows in the context of unconventional natural gas development in the Marcellus Shale.

Quantitative flow-ecology relationships are needed to evaluate how water withdrawals for unconventional natural gas development may impact aquatic ecosystems. Addressing this need, we studied current patterns of hydrologic alteration in the Marcellus Shale region and related the estimated flow alteration to fish community measures. We then used these empirical flow-ecology relationships to evaluate alternative surface water withdrawals and environmental flow rules. Reduced high-flow magnitude, dampened rates of change, and increased low-flow magnitudes were apparent regionally, but changes in many of the flow metrics likely to be sensitive to withdrawals also showed substantial regional variation. Fish community measures were significantly related to flow alteration, including declines in species richness with diminished annual runoff, winter low-flow, and summer median-flow. In addition, the relative abundance of intolerant taxa decreased with reduced winter high-flow and increased flow constancy, while fluvial specialist species decreased with reduced winter and annual flows. Stream size strongly mediated both the impact of withdrawal scenarios and the protection afforded by environmental flow standards. Under the most intense withdrawal scenario, 75% of reference headwaters and creeks (drainage areas <99km2 ) experienced at least 78% reduction in summer flow, whereas little change was predicted for larger rivers. Moreover, the least intense withdrawal scenario still reduced summer flows by at least 21% for 50% of headwaters and creeks. The observed 90th quantile flow-ecology relationships indicate that such alteration could reduce species richness by 23% or more. Seasonally varying environmental flow standards and high fixed minimum flows protected the most streams from hydrologic alteration, but common minimum flow standards left numerous locations vulnerable to substantial flow alteration. This study clarifies how additional water demands in the region may adversely affect freshwater biological integrity. The results make clear that policies to limit or prevent water withdrawals from smaller streams can reduce the risk of ecosystem impairment.

Patterns of Bat Distribution and Foraging Activity in a Highly Urbanized Temperate Environment.

Understanding how to manage biodiversity in urban areas will become increasingly important as density of humans residing in urban centers increases and urban areas expand. While considerable research has documented the shifts in biodiversity along urbanization gradients, much less work has focused on how characteristics of dense urban centers, effectively novel environments, influence behavior and biodiversity. Urban bats in San Francisco provide an opportunity to document changes in behavior and biodiversity to very high-density development. We studied (1) the distribution and abundance of bat foraging activity in natural areas; and (2) characteristics of natural areas that influence the observed patterns of distribution and foraging activity. We conducted acoustic surveys of twenty-two parks during 2008–2009. We confirmed the presence of four species of bats (Tadarida brasiliensis, Myotis yumanensis, Lasiurus blossevillii, and M. lucifugus). T. brasiliensis were found in all parks, while M. yumanensis occurred in 36% of parks. Results indicate that proximity to water, park size, and amount of forest edge best explained overall foraging activity. Proximity to water best explained species richness. M. yumanensis activity was best explained by reduced proportion of native vegetation as well as proximity to water. Activity was year round but diminished in December. We show that although bats are present even in very densely populated urban centers, there is a large reduction in species richness compared to that of outlying areas, and that most habitat factors explaining their community composition and activity patterns are similar to those documented in less urbanized environments.

Nitrogen effects on plant species richness in herbaceous communities are more widespread and stronger than those of phosphorus

Both nitrogen (N) and phosphorus (P) enrichment are known to impact plant diversity globally. Recent studies suggest that P enrichment may be as important, or even more important, as a driver of terrestrial plant species loss as N enrichment. However, the generality and relative contribution of these critical nutrients to species losses remains unclear. Here, we quantitatively compared effects of N, P and combined NP enrichment on species richness of natural and semi-natural herbaceous ecosystems across the world in a meta-analysis of 189 long-term nutrient addition experiments in the field. Our experiment-based approach shows that, across terrestrial and wetland ecosystems, N and NP enrichment had widespread and strong negative effects on plant species richness. N reduced plant species richness across experiments by on average 16% (p<0.001), while P did not (on average 3%, NS). Combined NP enrichment also reduced species richness, by on average 16% (p=0.009), with the dominant effect statistically attributed to N. N enrichment effects were greater in China than in Europe and America, which may be explained by background atmospheric N deposition rates and earlier species losses in Europe and America. P enrichment reduced species numbers only in the most species-rich communities and even increased species numbers at high latitudes. All nutrient enrichment combinations (N, P, NP) stimulated aboveground biomass production, and biomass-mediated mechanisms are likely to have contributed to reported species losses. Our findings demonstrate that for the protection of the world's herbaceous plant diversity, it is of the highest priority that N loads be drastically reduced.

Epiphytic ferns in swamp forest remnants of the coastal plain of southern Brazil: latitudinal effects on the plant community

Community structure and spatial distribution of epiphytic ferns in swamp forest remnants along the coastal plain of the state of Rio Grande do Sul were analyzed. A total of 440 trees were sampled in fifty-seven 10 x 10 m plots. Each phorophyte was divided into five ecological zones (strata), where all species of epiphytic ferns were recorded. A total of 34 species representing 18 genera in six families were recorded. Polypodiaceae was the most represented family with 17 species, and Microgramma vacciniifolia had the highest epiphytic importance value. Characteristic holoepiphyte was the predominant ecological category, representing 70 % of the species. Ordination analysis showed a gradual change in floristic composition between ecological zones with richness differing significantly between strata. We observed that with increasing latitude there was a decrease in mean temperature and total rainfall, but an increase in frosts. These climatic and phytogeography changes result in a reduction in species richness and a change in the structure of epiphytic fern communities in a north-to-south direction. The importance of swamp forest remnants of the coastal plain to the diversity of epiphytic ferns is discussed.

Multiple Browsers Structure Tree Recruitment in Logged Temperate Forests.

Historical extirpations have resulted in depauperate large herbivore assemblages in many northern forests. In eastern North America, most forests are inhabited by a single wild ungulate species, white-tailed deer (Odocoileus virginianus), and relationships between deer densities and impacts on forest regeneration are correspondingly well documented. Recent recolonizations by moose (Alces americanus) in northeastern regions complicate established deer density thresholds and predictions of browsing impacts on forest dynamics because size and foraging differences between the two animals suggest a lack of functional redundancy. We asked to what extent low densities of deer + moose would structure forest communities differently from that of low densities of deer in recently logged patch cuts of Massachusetts, USA. In each site, a randomized block with three treatment levels of large herbivores–no-ungulates (full exclosure), deer (partial exclosure), and deer + moose (control) was established. After 6–7 years, deer + moose reduced stem densities and basal area by 2-3-fold, Prunus pensylvanica and Quercus spp. recruitment by 3–6 fold, and species richness by 1.7 species (19%). In contrast, in the partial exclosures, deer had non-significant effects on stem density, basal area, and species composition, but significantly reduced species richness by 2.5 species on average (28%). Deer browsing in the partial exclosure was more selective than deer + moose browsing together, perhaps contributing to the decline in species richness in the former treatment and the lack of additional decline in the latter. Moose used the control plots at roughly the same frequency as deer (as determined by remote camera traps), suggesting that the much larger moose was the dominant browser species in terms of animal biomass in these cuts. A lack of functional redundancy with respect to foraging behavior between sympatric large herbivores may explain combined browsing effects that were both large and complex.

Structural uncertainty in models projecting the consequences of habitat loss and fragmentation on biodiversity

Ecological theory is essential to predict the effects of global changes such as habitat loss and fragmentation on biodiversity. Species–area relationships (SAR), metapopulation models (MEP) and species distribution models (SDM) are commonly used tools incorporating different ecological processes to explain biodiversity distribution and dynamics. Yet few studies have compared the outcomes of these disparate models and investigated their complementarity. Here we show that the processes underlying SAR (patch area), MEP (patch isolation) and SDM (environmental conditions) models can be compared with a common statistical framework. Our approach allows for species and community‐level predictions under current and future landscape scenarios, facilitates multi‐model comparison and provides the machinery for integrating multiple mechanisms into one model. We apply this framework to the distribution of eight focal vertebrate species in current and future projected landscapes where 10% of the landscape is lost to land‐use change in southwestern, Quebec, Canada. Based on a model selection approach, we found that a model including patch area was the top ranked model for four of our focal species and models including patch isolation and environmental conditions were the top ranked models for two focal species each. Community‐level predictions of models based on patch area, patch isolation and environmental conditions for both current and future landscapes showed high spatial overlap, however, patch area models always predicted a reduction of species richness per patch whereas both the patch isolation and environmental conditions models predicted an increase or decrease in species richness per patch following habitat loss and fragmentation. Our comparative tool will allow ecologists and conservation practitioners to relate structural uncertainty to key mechanisms underlying each model. Ultimately, this approach is one step in the direction of deriving robust predictions for the change and loss of biodiversity under global change, which is key for informing conservation plans.

Novel Culturing Techniques Select for Heterotrophs and Hydrocarbon Degraders in a Subantarctic Soil.

The soil substrate membrane system (SSMS) is a novel micro-culturing technique targeted at terrestrial soil systems. We applied the SSMS to pristine and diesel fuel spiked polar soils, along with traditional solid media culturing and culture independent 454 tag pyrosequencing to elucidate the effects of diesel fuel on the soil community. The SSMS enriched for up to 76% of the total soil diversity within high diesel fuel concentration soils, in contrast to only 26% of the total diversity for the control soils. The majority of organisms originally recovered with the SSMS were lost in the transfer to solid media, with all 300 isolates belonging to Proteobacteria, Firmicutes, Actinobacteria or Bacteroidetes, the four phyla most frequently associated with soil culturing efforts. The soils spiked with high diesel fuel concentrations exhibited reduced species richness, diversity and a selection towards heterotrophs and hydrocarbon degraders in comparison to the control soils. Based on these observations and the unusually high level of overlap in microbial taxa observed between methods, we suggest the SSMS holds potential to exploit hydrocarbon degraders and other targets within simplified bacterial systems, yet is inadequate for soil ecology and ecotoxicology studies where identifying rare oligotrophic species is paramount.

ROÇAGEM E APLICAÇÃO DE HERBICIDA PARA CONTROLE DE&lt;i&gt; Megathyrsus maximus&lt;/i&gt;: DANOS SOBRE A VEGETAÇÃO PREEXISTENTE EM UM REFLORESTAMENTO DE 20 ANOS

A necessidade de controlar gramíneas exóticas em áreas de restauração ecológica por longos prazos pode acarretar elevados custos econômicos, danos colaterais à regeneração e danos menos óbvios ao ecossistema. Assim, dimensionar estes fatores negativos como parte do esforço para avaliar a razão custo/benefício das técnicas de controle dessas espécies, se faz necessário. Este estudo objetivou avaliar os danos causados por duas técnicas de controle de capim-colonião (Megathyrsus maximus (Jacq.) B. K. Simon &amp; S. W. L. Jacobs), sobre a regeneração preexistente (custos ambientais), em um reflorestamento de 20 anos, e estimar os custos econômicos do emprego dessas técnicas. Trinta parcelas de 10 x 20 m foram distribuídas em três grupos: (T1) controle, (T2) roçagem com roçadeiras costais e (T3) roçagem seguida da aplicação de herbicida à base de glifosato. Foi feito o inventário permanente de todos os indivíduos arbóreos e arbustivos, os quais foram acompanhados durante o período de um ano. Não houve diferença na mortalidade imposta pela roçagem inicial, tampouco na mortalidade imposta exclusivamente pela roçagem ou pelo herbicida no T3. Após um ano, não houve diferenças entre a mortalidade e a riqueza de espécies dos três grupos. Quando os três grupos foram comparados entre si após um ano, para as plantas &gt; 1 m, houve redução da abundância no T1 e redução da riqueza no T3; já para as plantas &lt; 1 m, houve redução da abundância no T2, e redução da abundância e riqueza no T3. Portanto, tais técnicas parecem afetar mais fortemente as plantas &lt; 1 m. O custo econômico final do T2 foi 34,1% maior do que o custo do T3, e mesmo que o custo para se realizar novas intervenções diminua para ambos, há aumento dos custos quando ocorre necessidade de intervenções esparsas em áreas pequenas. Ambas as técnicas são indicadas para controlar o capim-colonião, sendo que o uso de herbicida à base de glifosato deve ser restrito às áreas com baixa cobertura de dossel, por demandarem mais manutenções, e por ser a técnica mais prejudicial à regeneração, já que houve alta mortalidade de indivíduos de pequeno porte (73%) em áreas com densa infestação da gramínea (100%).

Post-Fire Recovery in Coastal Sage Scrub: Seed Rain and Community Trajectory.

Disturbance is a primary mechanism structuring ecological communities. However, human activity has the potential to alter the frequency and intensity of natural disturbance regimes, with subsequent effects on ecosystem processes. In Southern California, human development has led to increased fire frequency close to urban areas that can form a positive feedback with invasive plant spread. Understanding how abiotic and biotic factors structure post-fire plant communities is a critical component of post-fire management and restoration. In this study we considered a variety of mechanisms affecting post-fire vegetation recovery in Riversidean sage scrub. Comparing recently burned plots to unburned plots, we found that burning significantly reduced species richness and percent cover of exotic vegetation the first two years following a 100-hectare wildfire. Seed rain was higher in burned plots, with more native forb seeds, while unburned plots had more exotic grass seeds. Moreover, there were significant correlations between seed rain composition and plant cover composition the year prior and the year after. Collectively, this case study suggests that fire can alter community composition, but there was not compelling evidence of a vegetation-type conversion. Instead, the changes in the community composition were temporary and convergence in community composition was apparent within two years post-fire.

Diversity of palm communities at different spatial scales in a recently fragmented tropical landscape

AbstractHabitat loss and landscape fragmentation are often associated with changes in biological communities at different spatial scales. Our goal in this study was to identify fragment characteristics and environmental variables linked to palm species richness, abundance and community similarity at local and landscape spatial scales and to contrast these patterns between adults and juveniles. We sampled palm communities in 22 fragments of Chocó rainforest in and around the Mache-Chindul Ecological Reserve in north-western Ecuador, where we recorded 9991 individuals of 23 palm species. At the landscape scale, fragment size and surrounding forest cover were not associated with species richness or abundance for either adults or juveniles. However, community similarity of juveniles was related to surrounding forest cover and the abundance of juveniles and adults increased with elevation. At the local scale, adults and juveniles differed in their relationships to environmental variables and distance to fragment edge: juveniles showed reduced species richness and different community composition near fragment edges compared with interior habitat, but adults did not. These results provide baseline information on palm communities in a poorly studied conservation hotspot and highlight the importance of considering multiple spatial scales and life stages in studies of habitat fragmentation.

Agroforestry Practices Promote Biodiversity and Natural Resource Diversity in Atlantic Nicaragua.

Tropical forest conversion to pasture, which drives greenhouse gas emissions, soil degradation, and biodiversity loss, remains a pressing socio-ecological challenge. This problem has spurred increased interest in the potential of small-scale agroforestry systems to couple sustainable agriculture with biodiversity conservation, particularly in rapidly developing areas of the tropics. In addition to providing natural resources (i.e. food, medicine, lumber), agroforestry systems have the potential to maintain higher levels of biodiversity and greater biomass than lower diversity crop or pasture systems. Greater plant diversity may also enhance soil quality, further supporting agricultural productivity in nutrient-limited tropical systems. Yet, the nature of these relationships remains equivocal. To better understand how different land use strategies impact ecosystem services, we characterized the relationships between plant diversity (including species richness, phylogenetic diversity, and natural resource diversity), and soil quality within pasture, agroforests, and secondary forests, three common land use types maintained by small-scale farmers in the Pearl Lagoon Basin, Nicaragua. The area is undergoing accelerated globalization following the 2007 completion of the region’s first major road; a change which is expected to increase forest conversion for agriculture. However, farmer agrobiodiversity maintenance in the Basin was previously found to be positively correlated with affiliation to local agricultural NGOs through the maintenance of agroforestry systems, despite these farmers residing in the communities closest to the new road, highlighting the potential for maintaining diverse agroforestry agricultural strategies despite heightened globalization pressures. We found that agroforestry sites tended to have higher surface soil %C, %N, and pH relative to neighboring to secondary forest, while maintaining comparable plant diversity. In contrast, pasture reduced species richness, phylogenetic diversity, and natural resource diversity. No significant relationships were found between plant diversity and the soil properties assessed; however higher species richness and phylodiversity was positively correlated with natural resource diversity. These finding suggest that small, diversified agroforestry systems may be a viable strategy for promoting both social and ecological functions in eastern Nicaragua and other rapidly developing areas of the tropics.

Assessing the natural and anthropogenic influences on basin-wide fish species richness

Theory predicts that the number of fish species increases with river size in natural free-flowing rivers, but the relationship is lost under intensive exploitation of water resources associated with dams and/or landscape developments. In this paper, we aim to identify orthomorphic issues that disrupt theoretical species patterns based on a multi-year, basin-wide assessment in the Danshuei River Watershed of Taiwan. We hypothesize that multiple human-induced modifications fragment habitat areas leading to decreases of local fish species richness. We integrally relate natural and anthropogenic influences on fish species richness by a multiple linear regression model that is driven by a combination of factors including river network structure controls, water quality alterations of habitat, and disruption of channel connectivity with major discontinuities in habitat caused by dams.We found that stream order is a major forcing factor representing natural influence on fish species richness. In addition to stream order, we identified dams, dissolved oxygen deficiency (DO), and excessive total phosphorus (TP) as major anthropogenic influences on the richness of fish species. Our results showed that anthropogenic influences were operating at various spatial scales that inherently regulate the physical, chemical, and biological condition of fish habitats. Moreover, our probability-based risk assessment revealed causes of species richness reduction and opportunities for mitigation. Risks of species richness reduction caused by dams were determined by the position of dams and the contribution of tributaries in the drainage network. Risks associated with TP and DO were higher in human-activity-intensified downstream reaches. Our methodology provides a structural framework for assessing changes in basin-wide fish species richness under the mixed natural and human-modified river network and habitat conditions. Based on our analysis results, we recommend that a focus on landscape and riverine habitats and maintaining long-term monitoring programs are crucial for effective watershed management and river conservation plans.