Invasion and Colonisation of a Tropical Stream by an Exotic Loricariid Fish: Indices of Gradual Displacement of the Native Common Pleco (<i>Hypostomus punctatus</i>) by the Red Fin Dwarf Pleco (<i>Parotocinclus maculicauda</i>) over Fifteen Years

<div><p>The introduction of invasive species represents a major threat to the integrity of stream-dwelling fish populations worldwide, and this issue is receiving increasing attention from scientists, in particular because of potential impact on biodiversity. In this study, we analysed the dispersal of an exotic loricariid fish the red fin dwarf pleco (<i>Parotocinclus maculicauda</i>) in a stream of the Atlantic Forest biome in coastal south-eastern Brazil and evaluated the effects of this invasion on the native loricariid common pleco (<i>Hypostomus punctatus</i>). Specimens were collected at eight sites located along the course of the stream over a 15-year period. The distribution and density of the two species were determined by the Successive Removal Method. The introduction of <i>P</i>. <i>maculicauda</i> occurred in the medium sector of the stream, and during the course of the study, the species dispersed to new sites further upstream. By the end of the study, it was found at all points upstream from the original site. <i>Hypostomus punctatus</i> was registered at all sample sites both before and after the introduction of <i>P</i>. <i>maculicauda</i>, but its density decreased at all upstream sites after the arrival of the exotic species. Our analysis shows that colonisation by <i>P</i>. <i>maculicauda</i> seems to have a negative effect on <i>H</i>. <i>punctatus</i> densities. The maintenance of <i>H</i>. <i>punctatus</i> densities at the sites not colonised by <i>P</i>. <i>maculicauda</i> reinforces the conclusion that the colonisation of the stream by the exotic species had deleterious effects on the density of the resident <i>H</i>. <i>punctatus</i> populations, either by direct or indirect action.</p></div

Downstream densities of <i>Hypostomus punctatus</i>.

<p>Fig 3. Temporal variation in the density of <i>Hypostomus punctatus</i> in the sites of Rio Ubatiba sites (A) 6, (B) 7, and (C) 8.</p

Study area and the dispersal of <i>P</i>. <i>maculicauda</i>.

<p>Fig 1. Geographic location of Ubatiba stream system showing the dispersal of the dwarf pleco <i>Parotocinclus maculicauda</i> until 2009, following its introduction in 1999. The arrows indicate its suggestive dispersal, and the dates refer to the first record of the species at the respective site. The black line between sites 1 and 2 indicates the location of a waterfall.</p

Pairwise Spearman correlations between the densities of <i>H</i>. <i>punctatus</i> and <i>P</i>. <i>maculicauda</i>, and the first and second PCA axes.

<p>The correlation coefficient, <i>r</i>, is shown above the diagonal, and tCe <i>P</i> values are shown below the diagonal (italics).</p

Frequency of electrofishing samples collection at the Rio Ubatiba between 1994 and 2009.

<p>Frequency of electrofishing samples collection at the Rio Ubatiba between 1994 and 2009.</p

The eight different models based on the density of <i>Hypostomus punctatus</i> at the five sampling sites as the response variable, with all the possible combinations of independent variables (density of <i>Parotocinclus maculicauda</i>, and first and second PCA axes) were fitted and compared using Akaike’s Information Criterion and the relative weight (<i>w</i>_i) for each model.

<p>The best model, with the highest <i>w</i>_<i>i</i> value, includes the predictors <i>P</i>. <i>maculicauda</i> density and the second PCA axis.</p

Upstream densities of <i>Parotocinclus maculicauda</i> and <i>Hypostomus punctatus</i>.

<p>Fig 2. Temporal variation in the density of <i>Parotocinclus maculicauda</i> (black circles) and <i>Hypostomus punctatus</i> (grey squares) in the Rio Ubatiba at sites (A) 5, (B) 3, (C) 4, (D) 2, and (E) 1. Note that Y-axis is not at the same scale.</p