Common and rare species differ in their level of dispersal ability and habitat specialization, and thus should respond to distinct assembly rules. Rare species are much more spatially restricted and usually show higher habitat specialization, so they can be much more vulnerable to landscape changes than common species. We simulated three species-loss scenarios to assess how different groups of stream fish species respond to environmental and spatial variables and how potential extinctions affected regional functional richness and the average functional distinctiveness. Rare and common species contribute similarly to the global functional richness, but the loss of common species led to a marked decrease in local redundancy. Whilst intermediate and rare species are regulated by dispersal, dominant species respond to niche processes and are more affected by land-use changes. Therefore, common and rare species are under distinct assembly rules and may exhibit distinct responses in the face of environmental anthropization. Addressing rare species is often overlooked, despite constant claims regarding their importance and their frequently concerning conservation status. Accounting for their rarity can offer a more refined look at the responses of species to human modifications, providing valuable information on how to tackle biodiversity loss.Keywords Species loss Á Land-use changes Á Dispersal ability Á Environmental filtering Á Extinction Naraiana Loureiro Benone and Bruno Eleres Soares are sharing co-first authorship.
ABSTRACT. Bathygobius soporator (Valenciennes, 1837) is one of the most common fi shes in tide pools in the estuary of Pará state, and has an omnivorous feeding habit. This study examined the diet of the species in Maiandeua Island, and aimed to: (i) describe the diet of B. soporator through indexes based on the occurrence and weight of consumed items; and (ii) evaluate if there is variation in diet composition between males and females. Frequency of Occurrence, frequency of weight and Alimentary Index were calculated for each item, and diff erences in the diet composition of males and females were observed through multivariate analyses (ANOSIM, NMDS and SIMPER). Bathygobius soporator presented carnivorous feeding habit, eating mainly crustaceans, and diff erences among males and females were observed, males consuming smaller amounts of crustaceans and including algae in their diet.
KEYWORDS. Estuaries, diet, trophic guild.RESUMO. Diferença entre sexos na alimentação do peixe gobídeo Bathygobius soporator em poças de maré da Ilha de Maiandeua, Pará, Brasil. Bathygobius soporator (Valenciennes, 1837) é um dos peixes mais comuns em poças de maré no estuário paraense e apresenta hábito alimentar onívoro. Esse estudo examinou a dieta da espécie na Ilha de Maiandeua, com o objetivo de: (i) descrever a dieta de B. soporator através de índices baseados na ocorrência e biomassa dos itens alimentares; (ii) avaliar se há variação na composição da dieta entre machos e fêmeas. Calculou-se a frequência de ocorrência, frequência de peso e o Índice de Importância Alimentar, e utilizaram-se análises multivariadas (ANOSIM, NMDS e SIMPER) para avaliar a diferença na composição da dieta de machos e fêmeas. Bathygobius soporator apresentou hábito carnívoro, consumindo predominantemente crustáceos, e houve variação na dieta de machos e fêmeas, sendo que machos consumiram crustáceos em menor quantidade e incluíram algas em sua dieta.PALAVRAS-CHAVE. Estuário, dieta, guilda trófi ca.
The length‐weight relationship is important for the study of populational dynamics. This study aimed to describe the length‐weight relationships (LWR) of 11 fish species sampled on 18 streams of the Capim river basin on eastern Amazon. Specimens were captured in 2014, 2015 and 2017, using sieve nets with 2 mm of mesh size. Fixed specimens were fixed in 10% formalin and conserved in alcohol 70%, measured for standard length (SL, 0.1 cm) and total weight (W, 0.01 g). The 11 species analysed were: Hemigrammus bellottii, Hemigrammus ocellifer, Hyphessobrycon heterorhabdus, Iguanodectes rachovii, Copella arnoldi, Nannostomus trifasciatus, Apistogramma regani, Apistogramma agassizii, Gymnorhamphichthys rondoni, Hypopygus lepturus, Anablepsoides urophthalmus.
Species are going extinct 1,000 times faster than expected due to human impacts. When the extinction of species culminates in functional loss, ecosystem functioning is altered. Functional extinction risk depends on taxonomic and functional rarity, with the non‐redundant traits found in rare species being the most vulnerable.
To investigate the relationship between taxonomic rarity and functional extinction, we ran extinction simulations driven by taxonomic rarity. Firstly, we sampled the fish fauna of 40 pristine Amazonian streams and compiled functional traits related to the body size, defence, diet, stratification, and activity of species. Then, we removed species, beginning with the rarest and ending with the commonest (and vice‐versa) and compared the observed patterns with random extinction at local and regional scales.
Following the removal of rare species, the functional rarity and body size of the community both decreased, and functional extinctions occurred after less than 10% of extinction at both spatial scales. Otherwise, the removal of common species resulted in an increase in functional rarity at the local scale, although widespread species ensured the persistence of a set of unique functional traits at a regional scale. Additionally, more than 60% of the common species had to go extinct before any functional extinction occurred at either scale.
If the ongoing mass extinction targets rare species, Amazonian stream ecosystems will be impacted by the loss of fish species associated with vulnerable functions.
We propose an extinction risk assessment based on the ecosystem and recommend that future studies apply our approach to other taxa and ecosystems, to better understand the effects of human impacts on ecosystem functioning.
Spatial and temporal variations in streams promote large fluctuations of resource availability, thus affecting the diet of fishes. We evaluated the effects of hydrological periods and stream order within periods on the diet of the flag tetra Hyphessobrycon heterorhabdus. We analyzed 160 stomachs in eight streams ranging from 1st to 3rd order between dry and flood period. Sampled streams belonged to a well-preserved area in the Eastern Amazon. The flag tetra is omnivorous, with a tendency towards insectivory. During the dry period, the species exhibited a higher amount of autochthonous than allochthonous items. Fish consumed more allochthonous items in 1st and 2nd order streams in the dry period and in 1st and 3rd order streams in the flood period. These results reflect the interactions between temporal and longitudinal factors on resource availability and its influence on fish diet. This pattern is probably dependent on the extensive riparian vegetation as a direct and indirect source of food for stream fish.
Length‐weight relationships (LWR) and length‐length relationships (LLR) were analyzed for three species inhabiting tidepools in the Amazon Coastal Zone, two of them non‐native. Tidepools were sampled in five beaches along the Amazon Coastal Zone in 2011, and samplings were carried out using hand nets. The coefficients of allometry and proportionality were within the ranges estimated for fishes. All three species exhibited coefficients of allometry (b) higher than 3 in the LWR.
This study evaluated the reproductive characteristics of pike-characids, Boulengerella cuvieri, during the hydrological cycle in the Xingu River, eastern Amazon. The sex ratio was 1:1 and the gonado-somatic index and relative frequency of maturation stages indicate a short breeding season of single phase spawning that coincides with a filling and flood period. Mean standard length at first sexual maturity for female B. cuvieri was estimated to be 22·9 cm.
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