Decline In Species Richness Research Articles

Observations of marine species from whale watching vessels suggest that anthropogenic disturbance decreases biodiversity in the Pelagos Sanctuary

The Pelagos Sanctuary is a marine biodiversity hotspot, as well as a busy zone for vessel traffic. Long term research on cetaceans has been important in guiding management of this protected area; however, non-cetacean species have received less attention. For this study, we included cetacean and non-cetacean species in an assessment of biodiversity and the potential for anthropogenic disturbance to cause ecosystem stress, indicated by a decline in species richness or evenness. We analyzed sightings of marine wildlife collected on whale watching vessels operating from Imperia and Genova, Italy, using 95% minimum convex polygons to quantify survey area in each region. Our analysis indicated similar levels of species richness in both areas, however Genova had lower Simpson and Shannon-Wiener diversity indices than Imperia. This suggests that Genova has lower species evenness, with the community being more dominated by common species, while rare species are more elusive. Disturbance was quantified based on vessel traffic and fishermen long lines. Genova exhibited significantly higher levels of vessel traffic, but there was no evidence of a difference in disturbance from long lines. These results suggest that anthropogenic disturbance in Genova may result in more ecosystem stress than Imperia. Consequently, management programs should prioritize reducing the impact of vessel traffic on marine life in the northwest Mediterranean Sea.

The global problem of nuisance macroalgal blooms and pathways to its use in the circular economy

Macroalgal blooms are increasing globally as a result of anthropogenic stressors and are leading to negative environmental and socio-economic impacts. There is, however, an opportunity to utilise nuisance macroalgae by creating useful and economically viable products. Thus relieving pressure on diminishing, but sought-after natural resources. Here we have undertaken a systematic review of the literature to synthesise data from 639 peer-reviewed papers to: identify the spatial and temporal nature of macroalgal blooms; quantify the ecological and socio-economic impacts associated with these blooms; outline the conversion of macroalgal biomass into products, in particular for the main blooming genera; provide an assessment of input and product costs for different compounds; and provide feasibility assessments generated from Techno-Economic Analysis (TEA) and Life Cycle Assessments (LCA). Globally, green macroalgae (chlorophyta), predominately Ulva spp. (52%), were found to be the most reported and spatially distributed blooming algae. However, the largest single bloom was produced by Sargassum spp. (phaeophyta), producing >20 million tonnes in 2018. Ecologically, the dominant negative impacts of macroalgal blooms were a decline in species richness and abundance; with seagrasses and fish most impacted. Social and economic impacts of macroalgal blooms were under-reported in peer-reviewed papers and globally under-researched, but where reported, there were clear negative impacts. For nuisance green macroalgal species, biorefining to produce multiple products was the most researched application, yet in the feasibility assessments there was a stronger case for biofuel production. Limited TEA or LCA were identified focussing on bloom material. There is an urgent need for research to provide the tools for the effective utilisation of macroalgal blooms. We recommend increased research into bioprocessing and a TEA of nuisance macroalgal blooms especially for Ulva and other chlorophyta, which are predominantly problematic. If this is achievable then exciting pathways utilising problem macroalgae can be incorporated into the circular economy.

Marine Macrobenthos of NorthWest India-Reviewing the Known and Unknown

Tropical ecosystems sustain higher biodiversity and face faster species extinction. However, baseline information of these areas is either inadequate or scattered due to various reasons. The 2,360 km long coast of North West India (NWI), is a heavily industrialized and urbanized zone. This coast with unique biogeographical and climatic features with two notified marine protected areas also supports rich biodiversity. This review was motivated by a need to construct a synoptic view on marine benthic ecology and functioning by consolidating available information of macrobenthos. Two thousand seventy-eight macrobenthic taxa belonging to 14 phyla were compiled from 147 references and were composed mostly by Polychaeta (n= 617), Gastropoda (n= 602), and Bivalvia (n= 216). Habitat wise, intertidal and subtidal zones were more intensely studied and contributed most to the diversity records. Sediment texture and salinity were the major drivers of macrobenthic community structure in the subtidal areas and estuaries, respectively. In the intertidal zones, zonation patterns related to the tidal levels and time of exposure were distinct with the high water zones being sparsely populated and lower intertidal zones sustaining higher species and functional diversities. All zones of NWI coast were distinctly impacted to various extent by anthropogenic activities affecting the resident macrobenthos. Decline in species richness and species substitution due to pollution were reported in urbanized zones. Non-monsoonal months favored a more conducive environment for the macrobenthic diversity and functionality. Hypoxia tolerant polychaete species mainly belonging to Spionidae and Cossuridae dominated during the low oxygen conditions of upwelling and OMZ zones of NWI. Inadequate identification and inconsistency of sampling methods were major deterrents for concluding trends of distributions. Suggestions for future macrobenthic research include focusing on lesser studied groups and areas, seasonal as well anthropogenic hypoxic zones and well planned long-term monitoring studies. Major data lacunae were identified in the taxonomy, molecular, functional aspects, and bioinvasive studies of macrobenthos in this geographical zone despite clear evidence of high diversity of extant macrofauna. This compendium should help prioritize research areas and objectives aimed at enhancing our understanding of macrobenthos and improve predictive capabilities of community shifts that may occur due to global climate change scenarios.

Conversion of rainforest into oil palm and rubber plantations affects the functional composition of litter and soil Collembola.

Rainforest conversion and expansion of plantations in tropical regions are associated with changes in animal communities and biodiversity decline. In soil, Collembola are one of the most numerous invertebrate groups that affect the functioning of microbial communities and support arthropod predators. Despite that, information on the impact of changes in land use in the tropics on species and trait composition of Collembola communities is very limited. We investigated the response of Collembola to the conversion of rainforest into rubber agroforestry (“jungle rubber”), rubber, and oil palm plantations in Jambi Province (Sumatra, Indonesia), a region which experienced one of the strongest recent deforestation globally. Collembola were sampled in 2013 and 2016 from the litter and soil layer using heat extraction, and environmental factors were measured (litter C/N ratio, pH, water content, composition of microbial community and predator abundance). In the litter layer, density and species richness in plantation systems were 25%–38% and 30%–40% lower, respectively, than in rainforest. However, in the soil layer, density, species richness, and trait diversity of Collembola were only slightly affected by land‐use change, contrasting the response of many other animal groups. Species and trait composition of Collembola communities in litter and soil differed between each of the land‐use systems. Water content and pH were identified as main factors related to the differences in species and trait composition in both litter and soil, followed by the density of micro‐ and macropredators. Dominant species of Collembola in rainforest and jungle rubber were characterized by small body size, absence of furca, and absence of intense pigmentation, while in plantations, larger species with long furca and diffuse or patterned pigmentation were more abundant. Overall, land‐use change negatively affected Collembola communities in the litter layer, but its impact was lower in the soil layer. Several pantropical genera of Collembola (i.e., Isotomiella, Pseudosinella, and Folsomides) dominated across land‐use systems, reflecting their high environmental adaptability and/or efficient dispersal, calling for studies on their ecology and genetic diversity. The decline in species richness and density of litter‐dwelling Collembola with the conversion of rainforest into plantation systems calls for management practices mitigating negative effects of the deterioration of the litter layer in rubber plantations, but even more in oil palm plantations.

Influence of habitat features of urban streetscapes on richness and abundance of avian species

Abstract In human-dominated landscapes, roads are known to negatively influence birds causing decline in species richness, as well as reduction in the number of avian species. However, linear stretches of green spaces formed by roadside plantations in urban streetscapes can support diverse avian communities. In spite of being an integral habitat feature of urban areas, there is a clear paucity of studies on avian diversity in urban streetscapes. The present study was carried out in Kolkata, where data on avian species richness and abundance was collected from 16 randomly placed belt transects (replicates), each of 500 m length and 20 m width, on different major roads throughout the study area keeping a minimum gap of 200 m between adjacent transects to avoid data overlapping. Each of these transects were traversed on foot twice in a month from January to March 2017 during days with calm weather conditions. We recorded 31 species of birds belonging to 8 orders and 19 families, of which maximum species belonged to the order Passeriformes (13 species). We found that both abundance and species richness of birds in transects with higher number of trees (78±4.1 individuals and 19.55±1.703 species of birds) were significantly higher than transects with fewer trees (53.74±2.5 individuals and 9.5±0.789 species of birds). Amongst various habitat features along these streetscapes, the total number of trees positively influenced both species richness (GLMM: F1, 90=14.485, P<0.05) and abundance of birds (GLMM: F1, 90=8.081, P<0.05). However, the other land use variables (i.e. number of bushes, waterbodies, markets and buildings) neither influenced the abundance of birds nor the species richness. Our findings can be useful for urban development to perceive the importance of various habitat features in urban streetscapes in sustaining avian diversity.

A seven‐year study of the response of woodland birds to a large‐scale wildfire and the role of proximity to unburnt habitat

AbstractFire is a major ecological driver in many Australian ecosystems, and large‐scale wildfires can impact on faunal assemblages at a landscape scale. Monitoring the response of the avian community and individual bird species following a 92 039 ha wildfire in the Pilliga Forest, in temperate inland south‐eastern Australia, showed an initial decline in species richness and changes in community composition, followed by gradual recovery. Recovery was not complete by the end of the seven‐year study. Eighteen species (including Speckled Warbler Chthonicola sagittata and Eastern Yellow Robin Eopsaltria australis) were identified as likely to be fire sensitive and nine species (including Australian Magpie Cracticus tibicen and Red‐capped Robin Petroica goodenovii) as likely to respond positively to fire at the time scale of this study. Another 11 species (including Dusky Woodswallow Artamus cyanopterus and Jacky Winter Microeca fascinans) appeared to favour burnt areas close to the fire edge. Guild‐level patterns included an overall negative response to fire by insectivores, granivores/frugivores and declining woodland birds and a positive response by predators. The avian community recovered more quickly at burnt sites close to (within 2 km of) the fire edge compared to more remote sites more than 4 km from unburnt habitat, suggesting that proximity to unburnt areas (and therefore fire extent) is likely to be a key consideration in understanding the post‐fire recovery of birds.

The effects of long-term warming on arbuscular mycorrhizal fungal communities depend on habitat type on the Qinghai-Tibet Plateau

Arbuscular mycorrhizal fungi (AMF) are widespread root-associated microorganisms that participate in many ecosystem processes. However, the response of AMF communities to global warming still remains poorly understood, especially in high-altitude regions. This study investigated the responses of AMF communities to 17-year experimental warming with open top chambers in two habitat types (i.e., shrubland and meadow) of the alpine meadow ecosystem of the Qinghai–Tibet Plateau. For this, 454-pyrosequencing was used and the main ecological processes that structure AMF communities were inferred based on distributions of species abundance and phylogenetic patterns. A total of 110 different AMF phylotypes (shrubland habitat: 102; meadow habitat: 91) were identified in both habitats, predominantly belonging to Glomeraceae. Eighty AMF phylotypes were found in both habitats, and phylotypes affiliated with Acaulosporaceae and Archaeosporaceae were only found in the shrubland habitat. Warming did not affect AMF diversity or community composition in the shrubland habitat; however, in the meadow habitat, warming caused a decline of AMF species richness by 45.6%. Moreover, the taxon composition of AMF communities was changed via the negative influence of root biomass in the meadow habitat. Mandelbrot, based on the niche process, was the best-fitting model for all fungal data sets in both habitats, indicating that fungal community dynamics under warming treatments matched niche-based processes in both habitats. Moreover, the phylogenetic structure of AMF communities was always phylogenetically clustered regardless of warming in the shrubland habitat. However, the phylogenetic structure changed from phylogenetic clustering of the control treatment to random of warming treatment in the meadow habitat. This suggests that in the shrubland habitat, warming does not change the central ecological process that structures AMF communities, but rather, leads to the transformation of the central process from environmental filtration to the neutralization of habitat filtration and competition exclusion in the meadow habitat. In summary, these results indicate that the effect of long-term warming on the assemblage of AMF communities depends on the habitat type. This illustrates that maintaining a high habitat type complexity is conducive for the response of alpine meadow ecosystems to climate warming.

The effects of high-severity fires on the arboreal ant community of a Neotropical savanna.

Fire-suppression is of concern in fire-prone ecosystems because it can result in the loss of endemic species. Suppressing fires also causes a build-up of flammable biomass, increasing the risk of severe fires. Using a Before-After, Control-Impacted design, we assessed the consequences of high-severity fires on Neotropical savanna arboreal ant communities. Over a 9-year period, we sampled the ant fauna of the same trees before and after two severe fires that hit a savanna reserve in Brazil and the trees from an unburned savanna site that served as a temporal control. The ant community associated with the unburned trees was relatively stable, with no significant temporal variation in species richness and only a few species changing in abundance over time. In contrast, we found a strong decline in species richness and marked changes in species composition in the burned trees, with some species becoming more prevalent and many becoming rare or locally extinct. The dissimilarity in species richness and composition was significantly smaller between the two pre-fire surveys than between the pre- and post-fire surveys. Fire-induced changes were much more marked among species with strictly arboreal nesting habits, and therefore more susceptible to the direct effects of fire. The decline of some of the ecologically dominant arboreal ant species may be particularly important, as it opens substantial ecological space for cascading community-wide changes. In particular, severe fires appear to disrupt the typical vertical stratification between the arboreal and ground-dwelling faunas, which might lead to homogenization of the overall ant community.

Spatial and temporal variation in the species diversity of coastal California fish eggs

Ichthyoplankton studies can be used to assess the abundance, distribution, and reproductive activity of marine fishes, but few studies have monitored spawning activity at inshore sites. This study utilized weekly plankton sampling to construct a year-long time series of fish spawning at 6 pier sites along the California coast—Santa Cruz, San Luis Obispo, Santa Barbara, Santa Monica, Newport Beach, and La Jolla; sampling at the La Jolla site continues ongoing monitoring initiated in 2012. Fish eggs were sorted from the collected plankton and identified to species level using DNA barcoding of the COI and 16S genes. While only one year of data has been collected from 5 of the sites, the 2 sites north of Point Conception show markedly reduced diversity compared to the southern sites. Although the species observed reflect the local environment of each site, this pattern of reduced diversity at the northern sites is consistent with the well-documented decline in species richness with latitude along the California coast. The 7-year time series from La Jolla has revealed that spawning activity varies greatly among years, both in terms of egg production and species diversity, with a continuing trend of highest egg numbers in years with colder average winter sea surface temperature.

Species packing and the latitudinal gradient in beta-diversity.

The decline in species richness at higher latitudes is among the most fundamental patterns in ecology. Whether changes in species composition across space (beta-diversity) contribute to this gradient of overall species richness (gamma-diversity) remains hotly debated. Previous studies that failed to resolve the issue suffered from a well-known tendency for small samples in areas with high gamma-diversity to have inflated measures of beta-diversity. Here, we provide a novel analytical test, using beta-diversity metrics that correct the gamma-diversity and sampling biases, to compare beta-diversity and species packing across a latitudinal gradient in tree species richness of 21 large forest plots along a large environmental gradient in East Asia. We demonstrate that after accounting for topography and correcting the gamma-diversity bias, tropical forests still have higher beta-diversity than temperate analogues. This suggests that beta-diversity contributes to the latitudinal species richness gradient as a component of gamma-diversity. Moreover, both niche specialization and niche marginality (a measure of niche spacing along an environmental gradient) also increase towards the equator, after controlling for the effect of topographical heterogeneity. This supports the joint importance of tighter species packing and larger niche space in tropical forests while also demonstrating the importance of local processes in controlling beta-diversity.

Truncated bimodal latitudinal diversity gradient in early Paleozoic phytoplankton.

The latitudinal diversity gradient (LDG)-the decline in species richness from the equator to the poles-is classically considered as the most pervasive macroecological pattern on Earth, but the timing of its establishment, its ubiquity in the geological past, and explanatory mechanisms remain uncertain. By combining empirical and modeling approaches, we show that the first representatives of marine phytoplankton exhibited an LDG from the beginning of the Cambrian, when most major phyla appeared. However, this LDG showed a single peak of diversity centered on the Southern Hemisphere, in contrast to the equatorial peak classically observed for most modern taxa. We find that this LDG most likely corresponds to a truncated bimodal gradient, which probably results from an uneven sediment preservation, smaller sampling effort, and/or lower initial diversity in the Northern Hemisphere. Variation of the documented LDG through time resulted primarily from fluctuations in annual sea-surface temperature and long-term climate changes.

Sustainable Development of a Region. Case Study - Kazakhstan

The article provides an overview of the region's development, while suggesting how to assess sustainable development from the point of view of the ecological component, as well as social and economic. The paper presents a combination of assessments that used data and indicators (if any), as well as expert opinions for a comprehensive assessment. Although there are some key points and controversial issues, the development of Bayanaul l district can be assessed as sustainable. In general, there is a positive, general economic situation and the level of income of most people, good environmental conditions and rich biodiversity, stable social structure, and the identity of people in the area. On the contrary, there are various threats such as engineering and transport infrastructure, an increased flow of people from tourism, degradation of habitats, declining species richness and intensification of agriculture.

Tussock Circumference, Land Use Type and Drought Variably Influence Spider Assemblages Associated with Hyparrhenia hirta Grass Tussocks

Many human activities have an impact on the fauna and flora of the South African Grassland Biome, including agriculture, fire and urbanisation. Disturbances in grassland habitats often result in Hyparrhenia hirta, a native pioneer grass species, establishing dense stands. Here the assemblage composition, species richness and abundance of spiders associated with H. hirta tussocks was investigated at three grassland sites (annually burnt, suburban local road traffic and undisturbed control) in the central Free State Province of South Africa during winter 2015 and 2016. Further, inter-annual differences during a period of intense drought were evaluated. An increase in spider species richness, abundance and different assemblage composition with increased tussock height and basal circumference was expected, and we predicted these effects would differ between land use types. Overall, Tibellus spp. immatures (Philodromidae) and Poachelas striatus Haddad & Lyle, 2008 (Trachelidae) were the most abundant spider species, while Philodromidae and Gnaphosidae were the most abundant spider families at all three sites during both years. The most species-rich families were Gnaphosidae, Salticidae and Thomisidae. Over the two-year sampling period there was a significant decline in overall spider abundance (58.09 %) and species richness (28.17 %), which could be explained by the cumulative effects of a severe drought experienced in central South Africa during 2015 and 2016. Species richness and assemblage composition were influenced by tussock basal circumference and disturbance effects, but not by tussock height. Several species were associated with the control site, while certain diversity metrics of the burnt and road verge sites were more stable, pointing to the importance of primary productivity in the former and water in the latter, for spider diversity. Trade-offs related to disturbance need to be carefully considered when developing management strategies for biodiversity.

Impacts of invasive ant-hemipteran interaction, edge effects and habitat complexities on the spatial distribution of ants in citrus orchards

The Argentine ant, Linepithema humile, is an invasive ant species well established throughout subtropical climates in the United States. The Argentine ant disrupts natural ecosystems by displacing native ant species and associating with phloem-feeding insects, which they protect from natural enemies in exchange for honeydew excreted by the phloem-feeders. Thus, interactions between these ants and phloem-feeders can be an issue of critical importance in agroecosystems. In this study, we aimed to determine whether the presence or absence of another invasive pest, Asian Citrus psyllid (ACP), Diaphorina citri, adjacent habitat types, and edge complexity impact the species richness, activity, and distribution of ants including the Argentine ant within citrus groves in southern California. When ACP were present and edge complexity was higher, ant activity rates were higher, yet we observed a decline in total ant species richness. Surrounding habitat type had no effect on ant activity or total ant species richness. Understanding the spatial patterns of both the Argentine ant and ACP can aid future management practices for controlling both Argentine ants and Asian citrus psyllid populations.

Changes in a peri‐urban butterfly assemblage over 80 years near Melbourne, Australia

AbstractAlthough changes, particularly declines, in Australian terrestrial insects and other invertebrates have long been suspected and well‐documented for some species, the magnitude, rate and spatial extent of decline remain unclear. Here we use a combination of alternative, qualitative approaches (expert opinion, historical records and temporal replication of surveys) to standardised monitoring and mapping programs to investigate the extent of change of a peri‐urban butterfly assemblage. This assemblage, comprising 52 species, of which 46 are residents or seasonal immigrants, was studied at three spatial scales (local ~0.01 km2, intermediate ~9 km2 and regional ~100 km2) in the Eltham district near Melbourne based on presence/absence data over the past 40 (1981–2020) and 80 years (1941–2020). We then consider the causal factors or drivers that have led to changes, and we explore the timing and ecological patterns underpinning extirpations. Long‐term records reveal substantial changes (mostly decline) in composition and species richness of the 46 breeding species at all spatial scales and time frames analysed. Although the magnitude and rate of decline were higher at the smaller, local to intermediate scales (29–43% decline over 40 years, loss rate of 0.20–0.25 species/year) compared with the larger, regional scale (26% decline over 80 years, loss rate of 0.15 species/year), extirpations at the larger scale were more alarming because they are indicative of widespread population collapse. Declines in relative abundance and occupancy were also recorded at the intermediate and regional spatial scales. Further decline (extinction debt) is anticipated for several ecological specialists currently known from very few sites. Historical extirpations mostly involved obligate myrmecophilous lycaenids and appear to have been largely driven by a combination of urbanisation (habitat loss, degradation and fragmentation) and vegetation encroachment. More recent extirpations consist mainly of grass‐feeding and mistletoe‐feeding specialists and are more worrying because they have predominantly occurred within the past 20–30 years. An interaction of urbanisation (tree canopy death and decline of mistletoes and their host trees from ecosystem dysfunction) and climate change (water stress and heat waves) are considered to be the most likely drivers for these ecological guilds.

Insect biomass decline scaled to species diversity: General patterns derived from a hoverfly community

Reports of declines in biomass of flying insects have alarmed the world in recent years. However, how biomass declines reflect biodiversity loss is still an open question. Here, we analyze the abundance (19,604 individuals) of 162 hoverfly species (Diptera: Syrphidae), at six locations in German nature reserves in 1989 and 2014, and generalize the results with a model varying decline rates of common vs. rare species. We show isometric decline rates between total insect biomass and total hoverfly abundance and a scale-dependent decline in hoverfly species richness, ranging between -23% over the season to -82% at the daily level. We constructed a theoretical null model to explore how strong declines in total abundance translate to changing rank-abundance curves, species persistence, and diversity measures. Observed persistence rates were disproportionately lower than expected for species of intermediate abundance, while the rarest species showed decline and appearance rates consistent with random expectation. Our results suggest that large insect biomass declines are predictive of insect diversity declines. Under current threats, even the more common species are in peril, calling for a reevaluation of hazards and conservation strategies that traditionally target already rare and endangered species only.

Palaeoecology and sea level changes: Decline of mammal species richness during late Quaternary island formation in the Montebello Islands, north-western Australia

Palaeoecology and sea level changes: Decline of mammal species richness during late Quaternary island formation in the Montebello Islands, north-western Australia

Worldwide occurrence records suggest a global decline in bee species richness

<h2>Summary</h2> Wild and managed bees are key pollinators, ensuring or enhancing the reproduction of a large fraction of the world's wild flowering plants and the yield of ∼85% of all cultivated crops. Recent reports of wild bee decline and its potential consequences are thus worrisome. However, evidence is mostly based on local or regional studies; the global status of bee decline has not been assessed yet. To fill this gap, we analyzed publicly available worldwide occurrence records from the Global Biodiversity Information Facility spanning over a century. We found that after the 1990s, the number of collected bee species declines steeply such that approximately 25% fewer species were reported between 2006 and 2015 than before the 1990s. Although these trends must be interpreted cautiously given the heterogeneous nature of the dataset and potential biases in data collection and reporting, results suggest the need for swift actions to avoid further pollinator decline.

Relationships between resource availability and elevation vary between metrics creating gradients of nutritional complexity

Plant and animal community composition changes at higher elevations on mountains. Plant and animal species richness generally declines with elevation, but the shape of the relationship differs between taxa. There are several proposed mechanisms, including the productivity hypotheses; that declines in available plant biomass confers fewer resources to consumers, thus supporting fewer species. We investigated resource availability as we ascended three aspects of Helvellyn mountain, UK, measuring several plant nutritive metrics, plant species richness and biomass. We observed a linear decline in plant species richness as we ascended the mountain but there was a unimodal relationship between plant biomass and elevation. Generally, the highest biomass values at mid-elevations were associated with the lowest nutritive values, except mineral contents which declined with elevation. Intra-specific and inter-specific increases in nutritive values nearer the top and bottom of the mountain indicated that physiological, phenological and compositional mechanisms may have played a role. The shape of the relationship between resource availability and elevation was different depending on the metric. Many consumers actively select or avoid plants based on their nutritive values and the abundances of consumer taxa vary in their relationships with elevation. Consideration of multiple nutritive metrics and of the nutritional requirements of the consumer may provide a greater understanding of changes to plant and animal communities at higher elevations. We propose a novel hypothesis for explaining elevational diversity gradients, which warrants further study; the ‘nutritional complexity hypothesis’, where consumer species coexist due to greater variation in the nutritional chemistry of plants.

Species Diversity, Distribution and Abundance of Fishes of Seti Gandaki River Basin, Pokhara, Nepal

Species diversity with indices, distribution and abundance of fishes of Seti Gandaki River Basin, Pokhara, Nepal are described from five study sites, three along the main channel and two in major tributaries. Fishes were sampled using a cast-net following pass-removal method. Environmental variables were determined following the standard methods. In total, 30 species belonging to five orders, nine families and 24 genera with absolute abundance of 10,659 were recorded. A longitudinal pattern of distribution and species richness from upstream to downstream sites (17 to 21 species) was observed. Cyprinids were dominant followed by silurids, balitorids, channids, mastacembelids, belonids and cobitids. Distribution pattern and abundance data showed that the species Tor tor, Tor putitora, Chaguninus chagunio, Barilius barila, Opsarius barna, Danio rerio, Lepidocephalichthys guntea, Parachiloglanis hodgarti and Amblyceps mangois were not common in the study area. The environmental variables such as depth, width, discharge and temperature showed effect upon species richness, abundance, distribution and diversity indices, which had lower values at upstream pre-urban sites than at downstream post-urban sites. A sharp decline in species richness, abundance and diversity indices at urban site (10 species) indicated urban influence.