DOI: 10.5061/dryad.nvx0k6dq5
title: Historical legacies and contemporary processes shape beta diversity in Neotropical montane streams

description: Aim Contemporary dispersal constraints and environmental conditions are
 broadly recognized as significant drivers of beta diversity patterns.
 However, beta diversity patterns may also reflect the legacy of past
 climatic and geological events. In this study, we investigated the
 relative importance of historical and contemporary factors as drivers of
 taxonomic, functional and phylogenetic beta diversity in Neotropical
 stream communities. Location The Colombian Orinoco basin. Major taxa
 studied Diatoms and insects. Methods We estimated taxonomic, phylogenetic,
 and functional beta diversity using Baselga’s (BAS) and Podani’s (POD)
 frameworks. Following both frameworks, we further partitioned every
 biodiversity facet into turnover and nestedness or richness difference
 components. Then, we used generalized linear models (GLM) to relate each
 biodiversity facet with environmental, spatial and historical factors.
 Results We found that both historical and contemporary factors affected
 current patterns of beta diversity. Historical factors and water pH and
 temperature had the strongest effect on beta diversity patterns,
 particularly for taxonomic and phylogenetic facets. GLM models performed
 better for insects than for diatoms in all three facets. Within
 communities, our analysis also revealed a partial congruence between BAS-
 and POD-based results. Main conclusions Due to their past geological
 history and contemporary environmental gradients, tropical montane streams
 are natural laboratory for disentangling the joint effects of ecological
 and biogeographical factors on biodiversity patterns. Our study reveals
 that present-day distribution patterns cannot be fully explained without
 accounting for the effects of past geological and climatic events on
 mountain landscapes. In the Neotropics, montane geology sets the stage for
 speciation and landscape formation, with which ecological (e.g., dispersal
 limitation) and environmental factors interact to generate spatial
 variation in species turnover.
description: <em>Study area </em> The Orinoco
 basin is the third largest basin in South America, covering an area of
 about 990,000 km2that is in most of Venezuela and in the eastern part of
 Colombia(Romero Ruz, Galindo Garca, Otero Garca, Armenteras Pascual,
 2004). The complex geological and climatic history of the basin has shaped
 a broad range of ecosystems across heterogeneous landscapes(Romero Ruz et
 al., 2004). In total, we sampled 26 (for diatoms) and
 32 (for insects) stream segments during the dry season of
 2017(January-February). In each stream segment (100 to 200m long), we
 selected three riffle areas that were representative of the range of
 substratum types, flow velocities, channel widths and depths, and canopy
 cover occurring along the stream. Physical and chemical variables were
 measured during invertebrate sampling (January-February 2017) and on two
 further occasions (November 2016 and, January-February 2018), that
 corresponded to high and low water flows, respectively. Instantaneous
 discharge was estimated in the three riffles by measuring of water depth
 and flow velocity at 15cm intervals along three cross-sections. At each
 interval, we also recorded the dominant substrate. Flow velocitywas
 measured with a digital flow meter (SCHILTKNECHT MiniAir 20). Canopy
 shading (%) was estimated from vertical photographs using a fisheye lens
 and subsequent image analysis.Conductivity, pH, oxygen, and temperature
 were recorded using a HANNA HI98194 water quality meter upon arrival
 (early morning) and departure (dawn) from the site. On
 each occasion, 1 L of water was collected for physico-chemical analyses,
 filtered through 0.7m glass fiber filters (Whatman GF/F, Kent, UK) and
 stored frozen until analysis. In the laboratory, ammonium and nitrate
 concentrations were determined on a Dionex ICS-5000 ion chromatography
 system (Dionex Corporation, Sunnyvale, U.S.A.). Reactive phosphorus (PRS)
 concentrations were determined colorimetrically using the fully automated
 discrete analyzer Smartchem 140 (AMS Allaince, Frpillon, France). Total
 suspended solids (TSS) were analyzed by filtering 500ml of water through a
 pre-weighed GFF and drying the filtrate for 1 hour at 105C. The mean and
 coefficient of variation of all the variables per ecoregion are summarized
 in Table S1. Longer-term hydrological variables were
 estimated using the rational method modified byTmez (2003). This method
 estimates a streams water flow as function of the total precipitation, the
 basin area and associated land uses, the time of concentration, and the
 runoff coefficient (Supplementary Material).Once the daily water flow had
 been determined, we estimated the threshold at which the streams basal
 flow was surpassed, as a unit of disturbance for the invertebrate
 communities.We then calculated: (i) the number of days elapsed since the
 last flood event (defined as the one doubling the basal flow discharge);
 (ii) the number of flood events; and (iii) the ratio between the maximum
 and basal flow discharges. <em>Invertebrate
 sampling </em> Insects were collected using a
 multi-habitat sampling procedure, with 5 Surber (mesh size: 350mm; area:
 0.09 m2) samples collected in stream substrata that were selected
 according to their corresponding habitat coverage. For instance, if a
 riffle was composed of 60% of boulders, 30% gravel, and 10% cobbles, 3
 Surber samples of the first, 1 of the second, and 1 of the third
 substratum type were collected.The substratum distribution in each riffle
 was evaluated visually using the Wentworth scale (mm, diameter-based) as a
 reference(Wentworth, 1922).We only sampled boulders (diameter 250mm)
 smaller than the sample frame. In six of the 32 streams sampled, only two
 riffle sections (10 Surber samples) were sampled because of problems with
 access. In the laboratory, invertebrates were sorted
 and identified to the genus level, followingTrivinho-Strixino Strixino
 (1995), Merritt Cummins (2008), Domnguez Fernndez (2009) and
 Gonzlez-Crdoba et al.(2015). Chironomidae and Ephemeroptera were dissected
 and mounted in Euparal following the protocol ofDomnguez (2006) and
 Andersen et al. (2013). The pupae of Chironomidae were mounted to confirm
 some taxonomical identities (Prat et al. 2014).
 <em>Diatom sampling </em> We
 sampled diatom communities at three different riffle sections of each
 stream segment, each section spanning from 20 to 60m long.At each riffle
 section, we collected 8 cm2of surface, brush-scraped algal material from
 30 boulders and cobbles. In the case of streams from Guiana shield and
 high-Plains, where boulders and cobbles were scarce, we also took samples
 from bedrock, pebbles and sand. Algal material was pooled by riffle
 section (= 3 samples per stream segment) and subsequently preserved in
 aTranseausolution. In the laboratory, the organic material from samples
 was cleaned using hydrogen peroxide. Clean diatom frustules were mounted
 on permanent slides using a Naphrax medium, the slides were then observed
 under a 1000x light microscope and identified at the finest level possible
 using specialized monographs(Krammer and Lange-Bertalot 1986, 1991,
 Metzeltin and Lange-Bertalot 2007, Bellinger and Sigee 2015). At least 400
 valves were counted in each slide.