SUMMARY1. Continuous multiyear data sets can help to detect long-term trends and allow predictions with respect to environmental and biological variables. While the use of taxon-based approaches for biomonitoring of watercourses is well established, little information exists concerning long-term variability of dominance and growth form composition of aquatic macrophyte communities. We analysed patterns in dominance and growth forms of macrophytes over a period of 21 years in relation to changes in water chemistry, disturbance regime and extreme weather conditions in two reference streams in the north-west German lowlands. 2. Rank-abundance curves of annual observations indicated five core species. The pattern of abundance resembled a broken-stick rather than a log-normal distribution. The core species, which reached both the highest absolute and average cover values, were Sparganium emersum, Elodea canadensis, Callitriche hamulata, Potamogeton natans and Ranunculus peltatus.3. An analysis of change in dominance showed that in 67.5% of all observed cases, the same species became dominant in the subsequent year. Sparganium emersum (80.6%) and E. canadensis (68.8%) were the most successful species in retaining their relative dominance. Calculation of transition probabilities showed a strong attractor function of states dominated by Sparganium and Elodea. However, dominance patterns broke down over time and after 20 years, only one of the sites still showed the same dominance type. On average, dominance was preserved for around 4 years. 4. Reaches were mostly dominated by six growth forms, namely vallisnerids, potamids, peplids, nymphaeids, myriophyllids and graminids. In each reach, two, three or five growth forms shared the highest cover percentages. An analysis of traits of successfully established and dominant species identified three strategies: a facultative wintergreen growth habit in combination with effective means of vegetative reproduction; strong maintenance traits (in particular rhizomes); short-life span in combination with seed and turion production. 5. Strong oscillations of growth form types were observed. Six growth form clusters were defined, up to four of which may occur in one reach. Most frequent clusters were one characterised by strong vallisnerid dominance and another characterised by dominant potamids with peplids and myriophyllids. Both clusters showed the highest frequencies, durations and transition probabilities from other clusters. On average, growth form clusters persisted for 4.5 years.6. An analysis of the influence of environmental factors on growth form dynamics showed that chemical and physical parameters distinguish the sample sites but cannot explain the observed changes. 7. We conclude that dynamics of species dominance as well as the occurrence of growth form assemblages are not controlled by physicochemical environmental factors such as nutrient composition at the scale of observation in this type of river. Instead, stochastic interactions between species characteristics and...
Increased human activities such as commodity-led deforestation, extension of agriculture, urbanization, and wildfires are major drivers of forest loss worldwide. In Cameroon, these activities cause a loss of suitable primate habitat and could ultimately threaten the survival of chimpanzees (Pan troglodytes). We derived independent estimates of the population size of the Endangered Nigeria–Cameroon chimpanzee (Pan troglodytes ellioti) in Kom-Wum Forest Reserve, Cameroon, and surrounding unprotected forest areas through 1) direct observations, 2) camera trapping, 3) distance sampling, 4) marked nest counts, and 5) standing crop nest counts. In addition, we georeferenced signs of chimpanzee and human activity along line transects. We used a generalized linear mixed model to predict the occurrence of chimpanzees in response to edge length (measured as the perimeter of core forest patches), core area of forest patches (measured as area of forest patches beyond an edge width of 100 m), habitat perforation (measured as the perimeter of nonforested landscape within core forest patches), patch size(measured as area of forest patches), and forest cover. Chimpanzee density estimates ranged from 0.1 (direct observation) to 0.9 (distance sampling) individuals km−2 depending on estimation method with a mean nest group size of 7 ± 5.4 (SD). The mean encounter rate for signs of chimpanzee activity was significantly higher in mature forests (2.3 signs km−1) than in secondary forests (0.3 signs km−1) and above 1000 m elevation (4.0 signs km−1) than below 1000 m (1.0 signs km−1). The mean encounter rate for signs of human activity was significantly higher in secondary (8.0 signs km−1) than in mature forests (0.9 signs km−1). Secondary forests, habitat perforation, and edge length had a significant negative effect on the occurrence of chimpanzee signs. Overall, human activity and forest degradation affected the number of observed chimpanzee signs negatively. Regular antipoaching patrols and reforestation programs in degraded areas could potentially reduce threats to populations of endangered species and may increase suitable habitat area.
a b s t r a c tIn the present study, we present a synopsis of two macrophyte surveys of physiographic units in northwest Germany carried out over one decade. Data were used to test a set of hypotheses on macrophyte distribution at the regional level. Rank-frequency curves resembled the broken stick model. Twentyone species of the 59 most frequent species occurred at high frequencies above 15%. Helophytes made up a high percentage (12 of 21) of the frequent species. Phalaris arundinacea was the most frequent species in both sampling periods. Most species showed no considerable change in frequency over time, among them the core hydrophytes. Spatial variation of species frequencies among physiographical units showed a unimodal distribution in relation to frequency. Spatial variation of frequencies of functional groups was significantly lower. Most uneven distribution among physiographical units was found in cryptogams. DCA ordinations of physiographical units showed a spatial gradient from alluvial plains to higher grounds units, which remained constant over time. CCA ordination of physiographical units in relation to environmental parameters identified two main axes, an altitudinal gradient and an alkalinity gradient. Species composition of units corresponded to the main landscape pattern of alluvial plains, glacial lowlands, and higher grounds on Mesozoic rock. Species diversity showed a complex behavior. Diverse units were found both in alluvial plains and glacial lowlands of intermediate elevation. The study may help defining regionally differentiated reference states for stream management, benchmarking indicator scores of species and avoiding application of assessment methods outside their range of applicability.
Abstract:The spatial structure and evolution of river networks offer tremendous opportunities to study the processes underlying metacommunity patterns in the wild. Here we explore several fundamental aspects of aquatic plant biogeography. How stable is plant composition over time? How similar is it along rivers? How fast is the species turnover? How does that and spatial structure affect our species richness estimates across scales? How do climate change, river management practices and connectivity affect species composition and community structure? We answer these questions by testing twelve hypotheses and combining two spatial surveys across entire networks, a long term temporal survey (21 consecutive years), a trait database, and a selection of environmental variables. From our river reach scale survey in lowland rivers, hydrophytes and marginal plants (helophytes) showed contrasting patterns in species abundance, richness and autocorrelation both in time and space. Since patterns in marginal plants reflect at least partly a sampling artefact (edge effect), the rest of the study focused on hydrophytes. Seasonal variability over two years and positive temporal autocorrelation at short time lags confirmed the relatively high regeneration abilities of aquatic plants in lowland rivers. Yet, OPEN ACCESSWater 2014, 6 869 from 1978 to 1998, plant composition changed quite dramatically and diversity decreased substantially. The annual species turnover was relatively high (20%-40%) and cumulated species richness was on average 23% and 34% higher over three and five years respectively, than annual survey. The long term changes were correlated to changes in climate (decreasing winter ice scouring, increasing summer low flows) and management (riparian shading). Over 21 years, there was a general erosion of species attributes over time attributed to a decrease in winter ice scouring, increase in shading and summer low flows, as well as a remaining effect of time which may be due to an erosion of the regional species pool. Temporal and spatial autocorrelation analyses indicated that long term hydrophyte biomonitoring, for the Water Framework Directive in lowland rivers, may be carried out at 4-6 years intervals for every 10 km of rivers. From multi-scale and abundance-range size analyses evidence of spatial isolation and longitudinal connectivity was detected, with no evidence of stronger longitudinal connectivity (fish and water current propagules dispersal) than spatial isolation (bird, wind and human dispersal) contrary to previous studies. The evidence for longitudinal connectivity was rather weak, perhaps resulting from the effect of small weirs. Further studies will need to integrate other aquatic habitats along rivers (regional species pool) and larger scales to increase the number of species and integrate phylogeny to build a more eco-evolutionary approach. More mechanistic approaches will be necessary to make predictions against our changing climate and management practices.
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