Spatial Patterns Of Tadpole Diversity And Its Environmental Determinants In Mount Emei

Exploring the spatial patterns of biodiversity along elevational gradients and the mechanisms driving them is a main focus in ecology,biogeography,and conservation biology.As the larvae of amphibians,tadpoles are primary consumers in aquatic ecosystems,playing important roles in the exchange of material,nutrient cycling and energy flow.This is especially true in those barren and fragile ecosystems that predator species were limited.Despite studies related to spatial patterns of biodiversity and its determinants have been conducted across regions and taxa,most of them are only focused on species richness.More importantly,tadpole diversity patterns were usually explored in aquatic ecosystems of tropical areas,studies are still needed to be conducted in other regions(e.g.,streams in temperate forest).In addition,the diversity patterns reflect which kind of community assembly rules of tadpole community in mountainous streams are not clear.In this present study,Mount Emei was selected as the study area to quantify the spatial patterns of tadpole diversity(in particular,functional diversity),as well as its microhabitat environmental determinants.Specifically,18 streams were first selected as the transects along an elevational gradient(485 – 2865 m).We then monitored tadpole communities and microhabitat environmental variables of each transect from May to June in2018 and 2019,respectively.After that,tadpole morphological traits were measured,and phylogenetic tree was constructed.The aims of the present study were to(1)investigate the species composition,elevational patterns and its microhabitat environmental determinants;(2)explore the elevational patterns of tadpole diversity(both taxonomic and functional diversity)and quantify the relative contribution of elevation and microhabitat environmental variables to the variation of tadpole diversity;(3)demonstrate tadpole community assembly rules based on phylogenetics and functional traits.The results are as follows:1.Species composition,elevational patterns and its microhabitat environmental determinants.During the two years field work,a total of 1496 individuals belonging to 20 species from6 families were sampled in 18 forest streams.The dominant species were Bufo gargarizans,Megophrys omeimontis,Oreolalax omeimontis,and Leptobrachium boringii.These species accounted for 79.31% of the total number of individuals.The number of Megophrys shapingensis,Oreolalax major,Oreolalax schmidti,Oreolalax popei,Microhyla fissipes,Amolops chunganensis,and Amolops granulosus tadpoles accounted for 1.81% of the total number,which can be considered as the rare species in the streams.These results illustrated that species richness and composition differed between streams located in different elevations.Specifically,there were 15 species in the low elevational areas(485-807 m),and 10 species in the medium elevational sites(828-1248 m).However,only eight species were detected in the high elevational regions(1320-1602 m).Four elevational generalists including Quasipaa boulengeri,M.omeimontis,O.omeimontis,and O.popei were detected from low to high elevational areas.The CCA model testing the relationships between microhabitat environmental variables and tadpole species composition was significant,and a total of eight microhabitat environmental variables(i.e.,pH,conductivity,dissolved oxygen,water temperature,current velocity,total nitrogen and chlorophyll a)had significant effects on the distribution of tadpoles.2.The elevational patterns and microhabitat environmental determinants of tadpole diversity.Our results demonstrated a hump-shape relationship between tadpole entities richness and elevation,indicating that more entities were detected at the middle elevational streams.However,there were no significant relationships between elevation and other taxonomic diversity indices(i.e.,Shannon index,Pielou evenness)or functional diversity indices(i.e.,functional richness,functional evenness,functional divergence,and functional specialization).Variance partitioning showed that the variation of different diversity indices explained by elevation was extremely low.Instead,microhabitat environmental variables(i.e.,water conductivity,current velocity,pH and water temperature)contributed largely to the variation of all the diversity indices.In addition,the joint effects of microhabitat environmental variables and elevation on the variation of diversity indices were also extremely low.Hierarchical partitioning analyses indicated that discrepancy exists on the contribution of microhabitat variables to diversity indices.3.Tadpole community assembly rules.The Blomberg’s K values of all the 11 functional traits were less than 1,which indicated weaker phylogenetic signal than expected by a Brownian motion model of trait evolution.However,although it was weak,the functional traits related to locomotion(except tail shape and body section shape)had significant phylogenetic signals.Phylogenetic diversity(i.e.,Faith’s PD)had a hump-shape response to the increasing of elevation,which was consistent with the response of species richness to the elevation.Based on phylogenetic diversity and functional traits related to locomotion,we detected a phylogenetic clustering in the low and high elevational areas,while a phylogenetic overdispersion in the middle elevational regions.In contrast,phylogenetic composition was detected based on functional traits described food acquisition in the low and high elevational areas,while a clustered phylogenetic composition was occurred in the middle elevational regions.In conclusion,the present study demonstrated that both elevation and microhabitat features shape tadpole composition,supporting the claim that the assembly of montane communities is determined by both spatial processes and environmental filtering.However,the explanation of elevation to diversity is extreme low.Tadpole taxonomic and functional diversity were strongly determined by microhabitat environmental features(i.e.,conductivity,current velocity,pH,and water temperature)in mountainous streams,providing evidences that microhabitat should be a priority in tadpole diversity conservation.Based on the results of phylogenetic and functional structure along an elevation gradient,habitat filtering is the main driver of the community assembly in the low and high elevational area,while limiting similarity is the primary driver in the medium elevational sites.The results also gave strong supports for a deterministic model of tadpole community assembly in mountainous streams,which is supported by niche hypothesis.Since tadpoles are important omnivorous consumers in mountainous streams,further study could focus on their trophic niche,and investigate how the change of tadpole functional diversity can affect food web structures and functions in forest stream ecosystems.