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Seasonal Dynamics of Benthic Macroinvertebrates in Four Equatorial Forest Streams in the Mvila Division, Southern Cameroon
Seasonal variations are responsible for many of the disturbances observed in watercourses. This study aims to evaluate the seasonal dynamics of benthic macrofauna in the Metyi, Bengo, Sounou, and Lo’o watercourses in the Mvila Division. Sampling of benthic macroinvertebrates was carried out in 12 stations using the multi-habit/indat approach, using a 30 cm square dip net fitted. 3404 individuals of benthic macroinvertebrates (43.48% relative abundance) were counted in long dry season (LDS), 1839 individuals (23.49% relative abundance) in short rainy season (SRS), 1696 individuals (21.67% relative abundance) in long rainy season (LRS), and 889 individuals of benthic macroinvertebrates (11.36% relative abundance) in short dry season (SDS). In terms of diversity, a total of 174 taxa were identified: 111 in the LDS, 106 in the SRS, 92 in the LRS, and 51 in the SDS. Shannon and Weaver’s diversity index showed the lowest value in SDS, while its highest value was recorded during SRS, as was Pielou J Equitability index. The similarity index suggests that the seasons differ from one another. The LDS had the highest species richness and abundance, while the SRS had the highest diversity value according to Shannon and Weaver.
Journal Article
Terrestrial Invertebrate Inputs Determine the Local Abundance of Stream Fishes in a Forested Stream
Transfer of energy from more productive donor habitats is frequently significant for the maintenance of consumers in the recipient habitats. Nevertheless, the connection between the distribution of consumers and allochthonous inputs has not been directly examined by field experiment. We present experimental evidence that terrestrial invertebrate inputs directly influence the distribution of stream fishes in a forested headwater stream. When terrestrial invertebrate input to the stream was experimentally reduced by using greenhouse covers, fish biomass also decreased dramatically. Despite the greater amounts of input in the control than in the reduced treatments, terrestrial invertebrates made up ∼90% of stomach contents in both treatments during the study period. Moreover, no difference in fish growth rates was evident between the treatments. These results provide experimental evidence that the flow of such allochthonous resources in the donor-controlled system can explain the distribution and dynamics of the consumer populations.
Journal Article
Asynchronous Forest-stream Coupling in a Fire-prone Boreal Landscape: Insights from Woody Debris
1 We used dendrochronology to reconstruct the transfer of coarse woody debris across a forest-stream interface in a fire-prone boreal landscape. A sequence of regulating factors was considered from source to sink of in-stream woody debris (SWD), including fire history at the landscape scale, patterns of post-fire recovery of riparian forest and inputs of SWD at the scale of a stream reach and its associated floodplain, and burial of SWD at an excavated site. 2 Fires occurred repeatedly in the studied landscape (at least in 1708, 1733, 1791, 1811, c. 1838, c. 1850, 1882, 1941 and 1998), and were generally patchy on the floodplain because of the firebreak effect of the riparian corridor. Unburned forest remnants were regularly generated at the stream margin, thus permitting temporally continuous but spatially localized transfer of woody material across the forest-stream interface. These remaining forest patches also increased forest resilience by dispersing seeds and promoting conifer re-establishment in burned areas. 3 Because of higher severity compared with previous fires, the 1941 fire burned almost everywhere on the floodplain, creating only a few widely isolated unburned forest remnants. Consequently, following an abrupt post-fire increase, SWD inputs almost completely ceased. In addition, post-fire recovery of the riparian wood source is slow because of the spatially restricted seed source. 4 In this alluvial stream, wood burial is faster than decay and largely determines the residence time of SWD. Because the residence time is about 150 years, the current density of SWD is high and contrasts sharply with the very low tree density at the stream margin. Although this long residence time helps maintain stream integrity while the forest is recovering from the 1941 fire, it is unlikely that SWD inputs would resume extensively before burial of the current SWD pool. 5 Our research exemplifies the potentially complex impacts of disturbances on material transfer between a source and a sink ecosystem. We conclude that when certain components of ecosystems are coupled by unidirectional flow, those components will behave asynchronously if a disturbance impact at the source ecosystem does not propagate rapidly to the sink and the source and the sink recover at different rates.
Journal Article
Prey use by web‐building spiders: stable isotope analyses of trophic flow at a forest‐stream ecotone
A forest‐stream trophic link was examined by stable carbon isotope analyses which evaluated the relationship of aquatic insects emerging from a stream to the diets of web‐building spiders. Spiders, aquatic and terrestrial prey, and basal resources of forest and stream food webs were collected in a deciduous forest along a Japanese headwater stream during May and July 2001. The δ13C analyses suggested that riparian tetragnathid spiders relied on aquatic insects and that the monthly variation of such dependence is partly associated with the seasonal dynamics of aquatic insect abundance in the riparian forest. Similarly, linyphiid spiders in the riparian forest exhibited δ13C values similar to aquatic prey in May. However, their δ13C values were close to terrestrial prey in both riparian and upland (150 m away from the stream) forests during June to July, suggesting the seasonal incorporation of stream‐derived carbon into their tissue. In contrast, araneid spiders relied on terrestrial prey in both riparian and upland forests throughout the study period. These isotopic results were consistent with a previous study that reported seasonal variation in the aquatic prey contribution to total web contents for each spider group in this forest, implying that spiders assimilate trapped prey and that aquatic insect flux indeed contributes to the energetics of riparian tetragnathid and linyphiid spiders.
Journal Article
First record of biogenic silica in the stomach content of freshwater turtles
Aquatic species such as fish and turtles consume sponges and plants, which are sources of biogenic silica. Sponges belong to the phylum Porifera, and species in the class Demospongiae produce siliceous spicules, while plants form phytoliths. Some turtle species adjust their diet according to ontogenetic stage, with most being predominantly omnivorous and predators of silicified organisms. Studies on the ingestion of biogenic silica by turtles remain scarce in freshwater environments. This study aimed to analyze the diversity of biogenic silica bodies in the stomachs of the species Phrynops geoffroanus. Specimens were captured in Iguaçu National Park (PNI), Paraná, a vital remnant of the Atlantic Forest. Individuals underwent biometric measurements, photographic documentation, and euthanasia using Thiopental (93 mg/kg), following strict ethical protocols. Biological material was sent to the State University of Maringá, where stomachs were extracted. Stomach contents were processed at the Laboratory of Paleoenvironmental Studies (LEPAFE) at the State University of Paraná (UNESPAR), treated with HNO₃ on a heating plate, and the resulting material was mounted on slides for analysis. Three specimens of Phrynops geoffroanus at different ontogenetic stages were examined. Stomach analysis revealed the presence of biogenic silica, including phytoliths, diatom frustules, and sponge spicules, with the highest concentration found in young individuals and the lowest in juveniles. The predominant phytolith types suggest interactions with grasses and Podostemaceae. Gemmuloscleres of Oncosclera navicella were identified in young and adult individuals, confirming predation on freshwater sponges. This study highlights the trophic ecology of Phrynops geoffroanus and its interaction with silicified organisms.
Journal Article
Riparian cover buffers the effects of abiotic and biotic predictors of leaf decomposition in subtropical streams
Stream functioning is energetically dependent on terrestrial vegetation due to the input of leaves. The decomposition process of this allochthonous resource may be controlled by leaf identity and abiotic and biological predictors that are also influenced by the presence of riparian cover. In subtropical Uruguayan streams, most of the riparian zones have been reduced, and the response of the decomposition process to the predictors may depend on the presence of riparian cover. We analyzed the importance of leaf identity and riparian cover on the abiotic and biotic predictors of leaf decomposition in rangeland streams, comparing two stream types (open canopy stream, OCS, and riparian forest stream, RFS). Decomposition experiments of native species (Eryngium pandanifolium and Schoenoplectus californicus) and the exotic Eucalyptus globulus were carried out. There were no significant differences in decomposition rate between the stream types; however, some predictors had significant, albeit differential, effects on the decomposition process depending on the presence of riparian forest. In OCS, the decomposition rates were positively influenced by NH4-N and streamflow but negatively by PO4-P, conductivity, and proportions of scrapers. Most of these variables had nonsignificant effects on decomposition rates in RFS. Experimentation procedures are needed to establish the mechanisms by which the presence of riparian cover modulates the response of the leaf decomposition to the effects of abiotic and biotic variables in subtropical streams. Leaf decomposition is much more affected by changes in leaf identity, suggesting that riparian changes that are accompanied by changes in leaf inputs may strongly affect this ecosystem function.
Journal Article
Integrating Field Data and a Meta-ecosystem Model to Study the Effects of Multiple Terrestrial Disturbances on Small Stream Ecosystem Function
Environmental stressors such as land development and climate change impact biodiversity from local to landscape scales. Meta-ecosystem models can be used to represent these important cross-ecosystem interactions, but these models are rarely applied to real ecosystems. Here, we derive a meta-ecosystem model based on empirical data from the island of Newfoundland, Canada to predict how terrestrial disturbances will impact the functioning of small boreal streams. We study the effects of disturbances common in boreal systems: logging, insect outbreaks, unpaved roads, and general human impacts captured by the human impact index. We collect in situ data from 28 streams and analyze geospatial data at three spatial extents to inform the structure and analysis of our meta-ecosystem model. We use disturbance simulations in our meta-ecosystem model to identify mechanisms for how individual terrestrial disturbances affect streams. Top statistical models for our empirical data show that (1) benthic invertebrate biomass and specific conductivity increase with road density, (2) dissolved nitrogen and Ephemeroptera, Plecoptera, and Trichoptera (EPT) index increase with logging and insect outbreaks, and (3) benthic invertebrate biomass and percent shredders decrease with human impact index. Based on our boreal meta-ecosystem model simulations, logging may change the form of energy entering the aquatic ecosystem and weaken apparent competition between benthic invertebrates, periphyton, and leaf litter. Our unpaved road simulations suggest low sediment loading at our study streams increases habitat heterogeneity. Along with improving our mechanistic understanding of forest–stream ecosystems, our integration of empirical data and mathematical modeling creates a framework for using meta-ecosystem models to inform natural resource management.
Journal Article
Temporal Beta Diversity of Bacteria in Streams: Network Position Matters But Differently for Bacterioplankton and Biofilm Communities
Concern about biodiversity loss has yielded a surge of studies on temporal change in α-diversity, whereas temporal β-diversity has gained less interest. We sampled bacterioplankton, biofilm, and riparian soil bacteria repeatedly across the open-water season in a pristine stream network to determine the level of temporal β-diversity in relation to stream network position and environmental variability. We tested the hypothesis that aquatic bacterial communities in isolated and environmentally heterogenous headwaters exhibit high temporal β-diversity while the better-connected and environmentally more stable mainstem sections support more stable communities, and soil communities bear no relationship to network position. As expected, temporal β-diversity decreased from headwaters toward mainstems for bacterioplankton. Against expectations, an opposite pattern was observed for biofilm. For bacterioplankton, temporal β-diversity was positively related to temporal variability in water chemistry. For biofilm bacteria, temporal variability was negatively related to variability in temperature. Temporal β-diversity of soil communities did not show any response to stream network position, but was strongly related to variability in the soil environment. The two aquatic habitats and riparian soils supported distinctly different bacterial communities. The number of ASVs shared between the soil and the aquatic communities decreased along the network, and more so for bacterioplankton. The higher temporal variability of bacterial communities in the headwaters likely results from temporally variable input of propagules from riparian soil, emphasizing the role of land–water connection and network position to bacterioplankton community composition. Overall, bacterial communities exhibited high temporal variability, highlighting the importance of temporal replication to fully capture their network-scale biodiversity.
Journal Article
Effects of litter diversity on decomposition and biological colonization of submerged litter in temperate and tropical streams
Detrital food webs of woodland streams depend on terrestrial litter input and, thus, are susceptible to changes in riparian cover. We assessed effects of litter species richness and quality on decomposition and associated biological communities in temperate deciduous forest and tropical rainforest streams. Three native litter species were incubated in each stream in all combinations (7 litter treatments, 3 richness levels) in coarse- (invertebrate access) and fine-mesh bags (no invertebrate access) and were sampled 5 times over 74 (temperate stream) or 94 d (tropical stream). Decomposition, and fungal biomass, sporulation, and species richness were measured for each treatment. Alnus glutinosa litter was incubated in both streams to assess effects of environmental and biological differences between streams on litter decomposition. Biological colonization (number of fungal species, fungal biomass) and activity (conidial production) were lower in the tropical than the temperate stream, despite its higher water temperature (24 vs 8°C). Mass loss for individual species reached 95% in the temperate and 60% in the rainforest stream. Decomposition rates in mixtures were unaffected by litter richness but could be predicted from their initial N, phenol, and lignin concentrations (leaf quality). In the temperate stream, Alnus decomposition in coarse-mesh bags was positively related to litter richness, and Alnus stimulated decomposition of mixtures. Microbial O2 consumption, fungal biomass accrual, aquatic hyphomycete sporulation rate and richness, and shredder abundance and richness were insensitive to litter richness. In the temperate stream, presence of tough litter inhibited invertebrate colonization of mixtures, whereas in the tropical stream, presence of soft litter stimulated invertebrate colonization of mixtures. Litter quality (species identity), not richness, was the main controller of decomposition of litter mixtures, and decomposition of litter in mixtures may differ from decomposition of individual species. Thus, disappearance or introduction of key species might affect organic matter processing in streams.
Journal Article