Navegando por Orientadores "GERHARD, Pedro"

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Acesso aberto (Open Access)
Clima, solo e água: importância de variáveis ambientais na determinação da distribuição potencial de peixes de rios e riachos amazônicos
(Universidade Federal do Pará, 2017-10-19) ALVAREZ, Facundo; MONTAG, Luciano Fogaça de Assis; http://lattes.cnpq.br/4936237097107099; GERHARD, Pedro; http://lattes.cnpq.br/5621269098705408
Estimating the spatial distributions of species is one of the main objectives of macroecology, especially when sampling efforts fail to reach the demographic knowledge of the target species. In this sense, the species distribution models (SDM) allow us to approach the fundamental niche of the species from the extrapolation of predictor variables. The Amazonas-Tocantins basin is characterized by a strong environmental and physical dynamics that act differently in the regional ichthyofauna at different spatial scales. Due to the differential perception of hábitats by the species, four species of rivers were included, Ageneiosus inermis, Acestrorhynchus falcatus, Pygocentrus nattereri and Plagioscion squamosissimus, and four species of streams, Crenuchus spilurus, Helogenes marmoratus, Helogenes marmoratus and Trichomycterus hasemani. The objectives of the study were: (i) To determine which set of predictor variables allows better spatial representations for the species of rivers and streams using SDM; and (ii) To evaluate the predictive power of MaxEnt to generate SDM of rivers and streams using different sets of Predictor variables. The spatial records that presented spatial autocorrelation were processed from the spThin package. To characterize the environmental dynamics, 78 predictors were divided into three treatments: PCA1 (climatic variables), PCA2 (climatic variables, slope and accumulated flow) and PCA3 (climatic variables, slope, accumulated flow, topographic and edaphic variables). MaxEnt software was used and configured from the ENMeval package. Two aspects can be observed in the results: the use of hydrological, topographic and edaphic variables allows to obtain more precise and spatially restricted representations than only climatic variables. In the second place, it is evident that, regardless of the dimensional complexity of the system, MaxEnt allows to obtain MDEs with high predictive power for both river species and species of streams. In the case of river species, the macroscopic predictors (climatic variables - PCA1) allowed to represent their environmental requirements and their wide spatial distributions. Meanwhile, climatic, hydrological, topographic and edaphic variables (PCA3) acted as environmental filters restricting the spatial distributions of both species of rivers and streams. The dimensional complexity of the system does not affect the spatial representation capacity of Maxent, observing that, in the case of species of streams MaxEnt showed greater capacity of spatial representation.
Acesso aberto (Open Access)
Comunidade de insetos bentônicos em igarapés do nordeste paraense - Amazônia Oriental
(Universidade Federal do Pará, 2012-08-31) MONTELES, Josinete Sampaio; GERHARD, Pedro; http://lattes.cnpq.br/5621269098705408
This study aimed to know the community of benthic insects in 17 streams in northeastern Pará, Eastern Amazonia under different land uses and investigate the variations in the abundance, richness and diversity of aquatic insect community to vegetation cover the immediate surrounding area (riparian zone) and landscape (slopes of the watershed where it enters the stream sampled). The benthic macroinvertebrates were collected between July and October 2010, the period of lowest rainfall. At each point were made to 10 Surber samples for quantitative analysis and three hand-net only qualitative character. To evaluate differences between the richness, EPT abundance and diversity, we used an ANOVA and cluster analysis to summarize the biotic data. For differences in the scales of study were then used an ANOSIM and routine SIMPER. Environmental characteristics were also evaluated searching to correlate them to the taxonomic composition and distribution of taxa by Canonical Correspondence Analysis (CCA). A total of 46,371 individuals were collected, in which 11,384 with Surber, distributed in 61 taxa with a predominance of aquatic insects. The highest abundances were observed Chironomidae, Ephemeroptera, Trichoptera and Coleoptera. Abundance, richness and EPT were greater in sections of streams to riparian vegetation and watershed predominantly of igapó anthropic forest (references). The environmental variables of greatest influence on the community were percentage of forest environment in the riparian zone, average water temperature, turbidity, percentage of coarse and fine litter, pH, flow channel and coefficient of variation of channel width. The results showed differences in community composition in relation to different land uses. Through the ecological descriptors, it was detected that the watershed with the highest percentage of anthropic forest area and successional and higher percentage of riparian vegetation surrounding (30m) showed better environmental conditions than those dominated pastures.
Acesso aberto (Open Access)
Estradas, alagados antrópicos, peixes e a fragmentação de redes fluviais em uma paisagem agrícola do Nordeste do Pará
(Universidade Federal do Pará, 2011-04-18) BREJÃO, Gabriel Lourenço; GERHARD, Pedro; http://lattes.cnpq.br/5621269098705408
Badly planned roads crossing streams can generate small impoundments in channel segments upstream these crossings, turning lotic environments into lentic ones. The aim of this work was to study the diversity and functional structure of fish communities in anthropic impoundments in northeastern Pará state. These impoundments are formed due to roads construction on the riverine network, with large or small impacts on the hydrological connectivity, subject that is largely ignored for Neotropical lotic systems. Eighteen reaches were sampled in seven streams: six crossed by roads, and one not crossed by roads, used as a reference. Five streams are located in the cities of Igarapé-Açu and Marapanim in an agricultural landscape, and two in the city of São Francisco do Pará in a forest matrix. Five of six streams crossed by roads showed the formation of large impounded areas. In these locations three reaches were selected to sample fish: one upstream, one inside, and another one downstream the impoundment. In the not impounded stream only two reaches, upstream and downstream the road crossing the channel, were selected. The selected environments were sampled once between June and November, 2010, using visual census techniques (ad libitum and linear transect) in 200 m extension reaches. Seventy three species distributed in six orders, 26 families and 63 genera were registered. Characiformes (38.4%) and Siluriformes (31.5%) were the most representative orders in species number. Characidae, with 15 species (20.5%), e Cichlidae, with 10 (13.7%), were the most representative families in species number. These species were organized in 18 functional trophic groups (FTG) formed according to the most frequency observed feeding tactics to and its observed spatial distribution during the diving sessions. The impoundments enforced modifications in the streams biotic (assemblage taxonomic and functional structure) and physical structure of the streams. These environments showed lower species richness, higher abundance and lower FTG diversity in relation to the upstream and downstream reaches. The impoundments showed larger width, depth and high temperature besides less average speed and dissolved oxygen when compared to the upstream and downstream reaches. The use of functional trophic groups approach allowed to understand how the riverine network fragmentation process interfere in the studied fish assemblage structure.