The Importance of Ambient Sound Level to Characterise Anuran Habitat

<div><p>Habitat characterisation is a pivotal step of any animal ecology study. The choice of variables used to describe habitats is crucial and need to be relevant to the ecology and behaviour of the species, in order to reflect biologically meaningful distribution patterns. In many species, acoustic communication is critical to individuals’ interactions, and it is expected that ambient acoustic conditions impact their local distribution. Yet, classic animal ecology rarely integrates an acoustic dimension in habitat descriptions. Here we show that ambient sound pressure level (SPL) is a strong predictor of calling site selection in acoustically active frog species. In comparison to six other habitat-related variables (i.e. air and water temperature, depth, width and slope of the stream, substrate), SPL had the most important explanatory power in microhabitat selection for the 34 sampled species. Ambient noise was particularly useful in differentiating two stream-associated guilds: torrents and calmer streams dwelling species. Guild definitions were strongly supported by SPL, whereas slope, which is commonly used in stream-associated habitat, had a weak explanatory power. Moreover, slope measures are non-standardized across studies and are difficult to assess at small scale. We argue that including an acoustic descriptor will improve habitat-species analyses for many acoustically active taxa. SPL integrates habitat topology and temporal information (such as weather and hour of the day, for example) and is a simple and precise measure. We suggest that habitat description in animal ecology should include an acoustic measure such as noise level because it may explain previously misunderstood distribution patterns.</p> </div

Multiple factorial analysis (MFA) of advertising male frogs microhabitat.

<p>a, b. MFA including all variables. c, d. MFA without the SPL variable. e, f. MFA without the slope variable. a, c, e. Mapping of individuals in the first two dimensions resulting from the MFA. Colours of the circles correspond to cluster attribution of the individuals obtained by the hierarchical cluster analysis. Full circles represent the individuals in the MFA space, and open squares the centres of clusters. Black cluster = ‘torrents’, red cluster = ‘ponds’, green cluster = ‘rivers’. b, d, f. Contribution of the quantitative variables to the MFA axes. The length of the vectors corresponds to the amplitude of the variable contribution. Orientations of vectors represent the correlation to the two represented axes. Groups of variables are colour-coded.</p

Dendrogram of the individual male frogs resulting from the hierarchical cluster analysis based on their microhabitats.

<p>The coloured rectangles correspond to the cluster attribution: black cluster = ‘torrents’, red cluster = ‘ponds’, green cluster = ‘rivers’. Inertia gain for additional dimensions is inset in the top left corner.</p

Table_S4

Call variables average values per species

Ecological and life history differences of 2 focal consumers in 3 reaches.

<p>Ecological and life history differences of 2 focal consumers in 3 reaches.</p

Time series plot for chlorophyll a and leaf matter.

<p>Raw data (circles) and predicted values (curves) from mixed model analyses of periphyton chlorophyll <i>a</i> accrual rates (left panels) and leaf decomposition (right panels). Responses in controls (C) are solid symbols and lines, exclosures (E) are hollow symbols and dashed lines. Periphyton biomasses were evaluated at day 20 or 21 of the experiment.</p

Mean (±1SE) response values in control (C) and exclusion (E) treatments for all three reaches. Significantly larger values (<i>P</i><.05) for each treatment pair indicated in bold.

<p>Chlorophyll <i>a</i> biomass and periphyton AFDM (ash-free dry mass) collected in week 3 for all reaches.</p><p>Invertebrate biomass and abundance collected after 4 weeks in upstream and midstream reaches, after 3 weeks in downstream reach.</p

Mean (±1SE) visitation by guppies, killifish and crabs in all three stream reaches during day and night.

<p>Total daily mean was based on 12 hr diel periods and weighted to compensate for fewer night observations.</p><p>NA = not applicable (guppies not present in upstream reach).</p