摘要:

AbstractFreshwater copepods were sampled in the La Plata River basin to identify the processes that affect beta diversity and to determine the main factors influencing their geographical distribution and patterns of endemism. Beta diversity patterns exhibited strong dissimilarity between locations; the turnover process was predominant and indicated a replacement of species along the basin. Redundancy analysis indicated the presence of two large sets of species separated geographically by a boundary zone, with several associated variables. Northern species were associated with water transparency and temperature, mean air temperature, mean air temperature during winter and minimum air temperature of coldest month, indicating that these species are not tolerant to low temperatures and are abundant in reservoirs that are common in the upper stretch of the Paraná River basin. Southern species were related with amplitude of air temperature, turbidity, total phosphorus and total suspended matter, indicating that these species are polythermic and have adapted to live in river stretches. From 20 environmental variables analyzed in our study, partial least squares analysis indicated four variables with increased retention of effects on copepod abundance: air temperature, minimum temperature of coldest month, turbidity and transparency. Because almost all of the species found in this study occurred across a wide range of habitat types, the cause of the separation between river and reservoir species could be considered to be more anthropogenic than natural, and it primarily affected species abundance. For certain members of the northern group of copepod species, distribution was dependent on high temperatures, whereas the distribution of the southern group indicated that the species were polythermic

ISSN:1442-9985    

DOI:10.1111/aec.12240

年代:2015

数据来源: WILEY

摘要:

AbstractWe compared seed fate (survival, mortality by rodent predators, desiccation and other causes) of the treeCavanillesia arborea(Malvaceae) in preserved old‐growth tropical dry forests and in nearby abandoned pasturelands inBrazil. For this purpose, we performed an experiment where 15 seeds were placed in the surroundings of 15 parental individuals in each habitat. These 450 seeds were monitored over four months. At the end of the experiment, seed predation by rodents was higher in forest (56.5%) than in pasture (8.9%) areas, but seed desiccation showed the opposite pattern (8.9%vs.80.4%). Mortality by desiccation was also faster in pasture than in forest areas, probably reducing their attractiveness to predators in these areas. None of the seeds placed in the pasture survived, whereas 26.2% of seeds became seedlings in forest areas. The absence of seedling recruitment ofCavanillesia arboreain pastures is likely a consequence of their incapacity to tolerate the harsh abiotic conditions in this habitat. Thus, forest conversion imposes a strong limitation to the long‐term population viability of this species. However, restoration and natural regeneration of abandoned pastures can recreate the forest structure and microclimatic conditions favourable to seed germination and seedling establishment. Remnant individuals ofCavanillesia arboreain agricultural landscapes may have a negligible contribution to current recruitment, but they can attract potential dispersers of pioneer species, with positive feedbacks to future recruitment during secondary success

ISSN:1442-9985    

DOI:10.1111/aec.12241

年代:2015

数据来源: WILEY

摘要:

AbstractSensitive and cost‐effective indicators of aquatic ecosystem condition inAmazon streams are necessary to assess the effects of anthropogenic disturbances on those systems in a viable and ecologically meaningful manner. We conducted the present study in the municipality ofParagominas, state ofPará, northernBrazil, where we sampled adult dragonflies in 50 100‐m‐long wadeable stream sites in 2011. We collected 1769 specimens represented by 11 families, 41 genera and 97 species. The suborderZygoptera contributed 961 individuals andAnisoptera 808. Among the 97 recorded species, nine were classified as useful indicators of ecological condition, with four species being associated with more degraded streams (threeAnisoptera, oneZygoptera) and five with more preserved streams (all wereZygoptera).Anisoptera (dragonflies) tend to provide more useful indicators of more degraded environments because they have more efficient homeostatic mechanisms and are more mobile, enabling them to tolerate a wider range of environmental conditions. By contrast,Zygoptera (damselflies) tend to provide a more useful role as indicators of more preserved environments and high levels of environmental heterogeneity because of their smaller body sizes and home ranges and greater ecophysiological restrictions. We conclude from our assessment of this low‐orderAmazonian stream system that (i) the occurrence of specific odonate species is strongly associated with the configuration of riparian vegetation, (ii) agricultural activities appear to be the main factor determining changes in the composition of odonate assemblages and (iii) these insects can act as useful indicators of the ecological consequences of riparian habitat loss and disturbance. Because generalist species invade moderately degraded areas, those areas may have high species richness but host few species ofZygoptera. Therefore, preserving dense riparian vegetation is necessary to maintain aquatic ecological condition, and that condition can be rehabilitated by planting new trees. Both require enforcing existing environmental regulations, various types of incentives and educating local com

ISSN:1442-9985    

DOI:10.1111/aec.12242

年代:2015

数据来源: WILEY