Selección denso-dependiente de microhabitat en Galaxias platei: un estudio experimental

Abstract

RESUMENGalaxias platei es la especie nativa de mayor distribución en la Patagonia Chilena, habitando ambientes fl uviales y principalmente lacustres. Utiliza variados hábitats, desde plataformas de arcilla consolidada a ambientes de sustrato fi no y otros con presencia de macrófi tas, vegetación leñosa o sustrato rocoso grueso. En este trabajo analizamos experimentalmente la selección de microhábitat de G. platei y su dependencia con la disponibilidad de refugio y la densidad de peces que lo utilizan. Para ello diseñamos experimentos con distintos niveles de refugio a diferentes densidades. Se recrearon microhábitats con refugio de canto rodado (sustrato grueso) y refugio de vegetación acuática, y microhábitats sin refugio de grava (sustrato fi no) y piedra plana simulando sustrato de arcilla consolidada. Las densidades probadas fueron 4, 8, 12 y 16 individuos. Encontramos que en todas las densidades, G. platei selecciona microhábitats con refugio y que al aumentar la densidad se produce un cambio en la preferencia desde microhábitats con vegetación hacia sustratos de canto rodado. Por el contrario, en todas las densidades probadas, los microhábitats sin refugio fueron rechazados signifi cativamente. Tanto la selección denso-dependiente de microhábitats, como la tendencia a un comportamiento gregario a mayor densidad de individuos, sugieren un comportamiento antidepredatorio de la especie. PALABRAS CLAVES:Experimentación, refugio, interacción intraespecífi ca, peces nativos, Patagonia. ABSTRACTGalaxias platei is the most broadly distributed fi sh specie in the Chilean Patagonia that inhabits in rivers and mainly in lakes systems. It occurs on varied habitats from clay platforms to thin substrates with presence of macrophytes, large woody debris and big boulders substrata. In this work we experimentally analyzed the microhabitat use of G. platei with dependence of refuge availability and fi sh density. We conduct experiments at different refuge levels for different fi sh densities. We build refuge microhabitat using boulders (thick substrate) and aquatic vegetation, and microhabitat without refuge using gravel (thin substrate) and slab stone to simulate a clay substrate. Fish densities tested were 4, 8, 12 and 16 individuals. G. platei select microhabitats with refuge at all densities tested, changing preference from vegetation to boulders at increasing density. Whereas, signifi cant selection against to all microhabitats without refuge at all densities. Density dependent use of microhabitat and the tendency to a gregarious behavior at high fi sh density, suggest an antidepredatory behavior of the specie.

A Community-Level, Mesoscale Analysis of Fish Assemblage Structure in Shoreline Habitats of a Large River Using Multivariate Regression Trees

“…Salmonid density in Patagonian lakes has been found to be negatively correlated with trophic level in G. platei of piscivorous body length (Correa et al, 2012), but no specimens of this size were caught in the San Pedro River. Laboratory studies have concluded that native galaxiids show some tendencies towards anti-predatory behaviour (Sobenes et al, 2013b), including increased swimming activity and reduced oxygen consumption but not including enhanced use of refugia in the presence of nonnative predators (Milano et al, 2010;Sobenes, 2013a). It is therefore unclear how much of the apparent segregation shown in the MRTs is as a result of predation, interference, predator avoidance or divergent habitat preferences.…”

“…Ordination showed that the mesohabitats of each bank had similar environmental characteristics, supporting the latter hypothesis. Furthermore, the low swimming capacity of many native species would render them vulnerable to isolation because of the width of the channel and the higher velocities found along the thalweg (García et al, 2012b;Sobenes et al, 2013b). More research into the swimming capacity and dispersal behaviour of these species is required in order to evaluate these hypotheses.…”

Invasive species and postglacial colonization: their effects on the genetic diversity of a Patagonian fish

“…An initial population size of n ¼ 100 000 was chosen as this is the expected maximum size of a G. platei population inhabiting a lake with an area of 10 000 m 2 (i.e. maximum expected density: 10 individuals m 22 ; [44]). We thus simulated a typical G. platei population inhabiting a salmonid-free lake.…”

Past, present, and future of a freshwater fish metapopulation in a threatened landscape

“…The 0% and 90% levels of population size reduction represented 2 extreme scenarios. For these analyses, we used the present genotypic data, a carrying capacity of 500 individuals/km 2 , as suggested for G. platei populations from Chile (Sobenes et al 2013), mean fecundity of 20,000 (Zama 1986), and parameters detailed in Supporting Information.…”