Papers by Guillermo de Mendoza
PLoS ONE, 2024
Nematodes disperse passively and are amongst the smallest invertebrates on Earth. Freeliving nema... more Nematodes disperse passively and are amongst the smallest invertebrates on Earth. Freeliving nematodes in mountain lakes are highly tolerant of environmental variations and are thus excellent model organisms in dispersal studies, since species-environment relationships are unlikely to interfere. In this study, we investigated how population or organism traits influence the stochastic physical nature of passive dispersal in a topologically complex environment. Specifically, we analyzed the influence of female proportion and body size on the geographical distribution of nematode species in the mountain lakes of the Pyrenees. We hypothesized that dispersal is facilitated by (i) a smaller body size, which would increase the rate of wind transport, and (ii) a higher female proportion within a population, which could increase colonization success because many nematode species are capable of parthenogenetic reproduction. The results showed that nematode species with a low proportion of females tend to have clustered spatial distributions that are not associated with patchy environmental conditions, suggesting greater barriers to dispersal. When all species were pooled, the overall proportion of females tended to increase at the highest elevations, where dispersal between lakes is arguably more difficult. The influence of body size was barely relevant for nematode distributions. Our study highlights the relevance of female proportion as a mechanism that enhances the dispersal success of parthenogenetic species, and that female sex is a determining factor in metacommunity connectivity.
Proceedings of the National Academy of Sciences, 2024
In mountain regions globally, climate change is reducing snowpack, advancing snowmelt, and alteri... more In mountain regions globally, climate change is reducing snowpack, advancing snowmelt, and altering environmental regimes of rivers born in these elevations. Here, we conducted an experiment simulating end-ofcentury vs. current flow regimes in Sierra Nevada mountain streams to examine impending shifts in biodiversity and ecosystem processes. Early snowmelt destabilized stream epilithic biofilm metabolism and altered key ecosystem functions such as insect production and emergence, via shifts in community composition, structure, and phenology (i.e., timing of development). Notably, some processes showed sensitivity to climate change on fine timescales, with implications for predatorprey synchrony. As climate continues to change quickly in high-altitude mountain ecosystems, the resilience of stream ecosystem functions may hinge on the presence of diverse ecological communities.
Hydrobiologia, 2024
The Younger Dryas-Holocene transition represents a period of significant thermal change, comparab... more The Younger Dryas-Holocene transition represents a period of significant thermal change, comparable in magnitude to modern warming, yet in a colder context and without the effect of anthropogenic disturbance. This is useful as a reference to tackle how biodiversity is affected by temperature in natural conditions. Here, we addressed the thermal change during this period in a southern Baltic coastal lake (Konarzewo Lake, Poland), as inferred by chironomid remains. We evaluated changes in chironomid communities and used Hill numbers to explore how commonness and rarity underlie biodiversity changes attributable to warming. We found evidence of warming at Konarzewo Lake during the Younger Dryas-Holocene transition, with inferred temperatures in the Younger Dryas period supporting the NW–SE gradient in Younger Dryas summer temperatures across Europe. Chironomid communities drastically
changed during the thermal transition. However, Hill numbers showed no response to temperature when rare morphotypes were emphasized (order q = 0) or a weak response when they were balanced with common morphotypes (order q = 1). Hill number of order q = 2, emphasizing the most common morphotypes, consistently increased with temperature
across different sample sizes or coverages. This illustrates how common morphotypes, rather than the rare ones, may boost biodiversity facing warming.
Diversity, 2023
Climate warming is expected to drive an upward altitudinal shift of species distributions in moun... more Climate warming is expected to drive an upward altitudinal shift of species distributions in mountain areas. In this study, we consider how environmental variables constrain the distribution of freshwater mollusks across elevations based on an extensive survey of the entire Pyrenean range. Results show that several altitude-related variables are significantly relevant for the distribution of all mollusks (i.e., temperature, sediment organic content). Others respond more precisely to some variables: fine substrate proportion increases the probability of finding Pisidium sensu lato (mostly Euglesa species), and the latter, the macrophyte presence, and Ampullaceana balthica. Despite the low acid-neutralizing capacity in many of the lakes, only the distribution of A. balthica was significantly constrained by this factor, independent from elevation. The results confirm a likely altitudinal expansion of the distributions of all species, particularly toward lakes with a summer surface temperature increasing above 12 °C. The pace of change is expected to differ among species according to different nonlinear thresholds in thermal response, which temperature value increases from Pisidium s.l. to Ampullaceana to Ancylus, and the taxon-specific sensitivity to substrates and chemical conditions.
Ecology, 2023
Biota in disturbance-prone landscapes have evolved a variety of strategies to persist long term, ... more Biota in disturbance-prone landscapes have evolved a variety of strategies to persist long term, either locally (resistance) or by regional recolonization (resilience). Habitat fragmentation and isolation can limit the availability of recolonization pathways, and thus the dynamics of post-disturbance community reestablishment. However, empirical studies on how isolation may control the mechanisms that enable community recovery remain scarce. Here, we studied a pristine intermittent stream (Chalone Creek, Pinnacles National Park, California) to understand how isolation (distance from a perennial pool) alters invertebrate community recolonization after drying. We monitored benthic invertebrate reestablishment during the rewetting phase along a ~2-km gradient of isolation, using mesh traps that selected for specific recolonization pathways (i.e., drift, flying, swimming/crawling, and vertical migration from the hyporheic). We collected daily emigration samples, surveyed the reestablished benthic community after 6 weeks, and compared assemblages across trap types and sites. We found that isolation mediated migration dynamics by delaying peak vertical migration from the hyporheic by ca. 1 day on average per 250 m of dry streambed. The relative importance of reestablishment mechanisms varied longitudinally–with more resistance strategists (up to 99.3% of encountered individuals) in the upstream reaches, and increased drift and aerial dispersers in the more fragmented habitats (up to 17.2% and 18%, respectively). Resistance strategists persisting in the hyporheic dominated overall (88.2% of individuals, ranging 52.9%–99.3% across sites), but notably most of these organisms subsequently outmigrated downstream (85.6% on average, ranging 52.1%–96% across sites). Thus, contrary to conventional wisdom, resistance strategists largely contributed to downstream resilience as well as to local community recovery. Finally, increased isolation was associated with a general decrease in benthic invertebrate diversity, and up to a 3-fold increase in the relative abundance of drought-resistant stoneflies. Our results advance the notion that understanding spatial context is key to predicting post-disturbance community dynamics. Considering the interaction between disturbance and fragmentation may help inform conservation in ecosystems that are subject to novel environmental regimes.
Ecology and Evolution, 2017
Nematode species are widely tolerant of environmental conditions and disperse passively. Therefo... more Nematode species are widely tolerant of environmental conditions and disperse passively. Therefore, the species richness distribution in this group might largely depend on the topological distribution of the habitats and main aerial and aquatic dispersal pathways connecting them. If so, the nematode species richness distributions may serve as null models for evaluating that of other groups more affected by environmental gradients. We investigated this hypothesis in lakes across an altitudinal gradient in the Pyrenees. We compared the altitudinal distribution, environmental tolerance, and species richness, of nematodes with that of three other invertebrate groups collected during the same sampling: oligochaetes, chironomids, and nonchironomid insects. We tested the altitudinal bias in distributions with t-tests and the significance of narrowranging altitudinal distributions with randomizations. We compared results between groups with Fisher’s exact tests. We then explored the influence of environmental factors on species assemblages in all groups with redundancy analysis (RDA), using 28 environmental variables. And, finally, we analyzed species richness patterns across altitude with simple linear and quadratic regressions. Nematode species were rarely biased from random distributions (5% of species) in contrast with other groups (35%, 47%, and 50%, respectively). The altitudinal bias most often shifted toward low altitudes (85% of biased species). Nematodes showed a lower portion of narrow-ranging species than any other group, and differed significantly from nonchironomid insects (10% and 43%, respectively). Environmental variables barely explained nematode assemblages (RDA adjusted R2 = 0.02), in contrast with other groups (0.13, 0.19 and 0.24). Despite these substantial differences in the response to environmental factors, species richness across altitude was unimodal, peaking at mid elevations, in all groups. This similarity indicates that the spatial distribution of lakes across altitude is a primary driver of invertebrate richness. Provided that nematodes are ubiquitous, their distribution offers potential null models to investigate species richness across environmental gradients in other ecosystem types and biogeographic regions.
Ecography, Dec 2016
Species distributions can be analysed under two perspectives: the niche-based approach, which foc... more Species distributions can be analysed under two perspectives: the niche-based approach, which focuses on species–environment relationships; and the dispersal-based approach, which focuses on metapopulation dynamics. The degree to which each of these two components affect species distributions may depend on habitat fragmentation, species traits and phylogenetic constraints. We analysed the distributions of 36 stream insect species across 60 stream sites in three drainage basins at high latitudes in Finland. We used binomial generalised linear models (GLMs) in which the predictor variables were environmental factors (E models), within-basin spatial variables as defined by Moran's eigenvector maps (M models), among-basin variability (B models), or a combination of the three (E + M + B models) sets of variables. Based on a comparative analysis, model performance was evaluated across all the species using Gaussian GLMs whereby the deviance accounted for by binomial GLMs was fitted on selected explanatory variables: niche position, niche breadth, site occupancy, biological traits and taxonomic relatedness. For each type of model, a reduced Gaussian GLM was eventually obtained after variable selection (Bayesian information criterion). We found that niche position was the only variable selected in all reduced models, implying that marginal species were better predicted than non-marginal species. The influence of niche position was strongest in models based on environmental variables (E models) or a combination of all types of variables (E + M + B models), and weakest in spatial autocorrelation models (M models). This suggests that species–environment relationships prevail over dispersal processes in determining stream insect distributions at a regional scale. Our findings have clear implications for biodiversity conservation strategies, and they also emphasise the benefits of considering both the niche-based and dispersal-based approaches in species distribution modelling studies.
Annals de la Delegació de la Garrotxa de la Institució Catalana d'Història Natural, Aug 2016
Studies of the aquatic macroinvertebrates in the region of La Garrotxa (Catalonia, NE Spain) are ... more Studies of the aquatic macroinvertebrates in the region of La Garrotxa (Catalonia, NE Spain) are relatively scarce. In this paper, we report the results of the sampling efforts carried out at 29 sites along the watercourses of La Garrotxa in the basins of the Ter and Fluvià rivers. Overall, we identified 163 invertebrate species, including 39 non-biting midges, 28 mayflies, 21 beetles, 19 caddisflies, 14 stoneflies, 14 dragonflies and damselflies, and 11 molluscs. Records of two species of non-biting midges (Diptera: Chironomidae) are new for the Iberian Peninsula: Micropsectra logani (Edwards) and Stempellinella flavidula (Johannsen). As well, we briefly comment on the contribution that this study makes to knowledge of the distribution of certain species, and the environmental conditions of the sampled watercourses.
Ecology and Evolution, 2015
Aiming to elucidate whether large-scale dispersal factors or environmental species sorting prevai... more Aiming to elucidate whether large-scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran’s eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in-lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in-lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances.
In book: Ecosistemes dels Països Catalans, Suplement Història Natural dels Països Catalans (David Bueno, dir.), Publisher: Enciclopèdia Catalana, Barcelona, pp.258-259, 2013
A ls Pirineus hi ha més d'un miler d'estanys petits que fan entre 0,5 i 10 ha de superfície (la m... more A ls Pirineus hi ha més d'un miler d'estanys petits que fan entre 0,5 i 10 ha de superfície (la majoria, menys de 3 ha) i menys de 12 m de fondària (mapa a la pàgina 256). Es distribueixen entre els 1.600 i els 2.900 m d'altitud i l'aigua és transparent i molt pobra en sals i nutrients.
Organohalogen compounds are some of the most notorious persistent pollutants disturbing the Earth... more Organohalogen compounds are some of the most notorious persistent pollutants disturbing the Earth biosphere. Although human-made, these chemicals are not completely alien to living systems. A large number of natural organohalogens, part of the secondary metabolism, are involved in chemical trophic interactions. Surprisingly, the relationship between organisms' trophic position and synthetic organohalogen biotransformation capability has not been investigated.
Freshwater Biology, 2012
1. Most high mountain lakes were free of fish until humans stocked them. This provides the opport... more 1. Most high mountain lakes were free of fish until humans stocked them. This provides the opportunity to study the extent to which predation constrains the thermal distribution of large macroinvertebrates, among lakes of a suitable temperature for them.
2. We analysed the distribution of aquatic beetles (Coleoptera, Dytisicidae, including the genera Agabus, Platambus, Hydroporus and Boreonectes) in a set of 82 lakes in the Pyrenees. Temperature was the most important variable explaining the overall distribution of dytiscids (out of 29 environmental variables considered). The presence of fish (i.e. salmonids) and macrophyte cover (plants provide refuge from predators) was also important. Indeed, either salmonids or macrophytes as single factors explained more of the variance in dytiscid distribution than temperature.
3. Further analysis showed that the presence of salmonids was particularly important for the medium-sized dytiscid Agabus bipustulatus. This species is generally eurythermic, although in the Pyrenees it is found mainly in cold lakes. This is attributed to predation pressure from fish, since the latter are more likely to be present in warm lakes. As a consequence, salmonids increase fragmentation of A. bipustulatus with respect to populations occupying lowland habitats.
4. Predation can therefore constrain the distribution of species to a fraction of habitats that appear suitable based on simple thermal responses. As humans also facilitate the dispersal of non-native fish, the consequent modification of distribution patterns in fresh waters could make it difficult to predict how distributions might change in relation to climate warming.
Hydrobiologia, 2010
The distribution of different macroinvertebrate groups inhabiting the littoral zone of 82 mountai... more The distribution of different macroinvertebrate groups inhabiting the littoral zone of 82 mountain lakes in the Pyrenees was investigated in relation to the altitudinal environmental gradient. For each lake, altitude, longitude and latitude, together with 28 environmental variables, relating to chemical and physical characteristics and to lake general productivity, were considered. Using Principal Component Analysis (PCA) we showed that the altitudinal environmental gradient (i.e. altitude and altitude-related variables) represented the largest gradient of environmental variability. We found that incidence was related to altitude in about 50% of macroinvertebrate groups, most relationships being inverse, and also that the number of macroinvertebrate groups found per lake was better described by a second-order polynomial function than by simple linear regression. However, this relationship was linear for a subset of high-altitude lakes above 2,500 m a.s.l., suggesting an ecological threshold around this altitude. Redundancy Analyses (RDAs) showed the importance of environmental factors varying with altitude for the distribution of macroinvertebrate groups. Organic matter, salmonid presence, fine substrate dominance, macrophyte coverage, temperature and altitude by itself were, in this order, the most relevant factors. Partial RDAs showed that different combinations of these variables contributed to the explanation of the distribution of each group. However, the variable that uniquely explained most variability differed from group to group. We conclude that the altitudinal gradient is a multi-faceted ecological factor, which impinges on each group by means of some specific environmental variable(s) that are particularly relevant for the life history of that group.
Limnetica, 2006
High mountain lakes offer research opportunities beyond what could be expected from their quantit... more High mountain lakes offer research opportunities beyond what could be expected from their quantitative relevance in the Earth system. In this article we present a brief summary of the research carried out in the lakes of the Pyrenees in the last twenty years by the group of limnology of the Centre for High Mountain Research (CRAM) of the University of Barcelona. The studies can be included in three main topics: life in extreme conditions, catchment-lake relationships and environmental changes.
In: VI Jornades sobre Recerca al Parc Nacional d'Aigüestortes i Estany de Sant Maurici (Espot, 8-10 October 2003), pp. 39-48. Departament de Medi Ambient i Habitatge. Generalitat de Catalunya, Barcelona, 2004
The study analyses the ecological and geographical factors underlying the distribution and abunda... more The study analyses the ecological and geographical factors underlying the distribution and abundance of macroinvertebrates in the Pyrenean lakes, through an extensive 'sampling of &2 lakes, The results show that the main gradient of variability indicates a directional change in the richness of taxonomical groups. Macroinvertebrate groups involved in the extremes of this gradient are Turbellaria and PLecoptera at the low-diversity extreme, and Amphipoda, Odonata, Hirudinea, Heteroptera, Ephemeroptera and Leptoceridae at the high-diversity extreme, The environrnental factors that covary with this main gradient are not only altitude and within lake factots such as temperature, nitrate, organic matter in the sediment and macrophyte ocurrence, but also catchment factors such as scree, meadow and coniferous forest dominance. A subset of nine lakes from Aigüestortes i Eslany de Sant Maurici National Park are localized along the gradient. The results obtained here indicate that these lakes tend to accumulate more group diversity than randomly expected.
Botanica Complutensis, 2003
A chorological compilation of the native Cytiseae Brecht. & J. Presl. tribe is presented from the... more A chorological compilation of the native Cytiseae Brecht. & J. Presl. tribe is presented from the ‘Comunidad de Madrid’ area. Localities and 10 x 10 km UTM coordinates distribution maps are shown for 20 species, belonging to Adenocarpus, Cytisus, Echinospartum, Erinacea, Genista, Lupinus, Pterospartum and Retama genera. The obtained results suggest that the chorological information compiled might be biased, in favour of more restrictedly distributed species.
Revista de Diagnóstico Biológico, 1999
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Papers by Guillermo de Mendoza
changed during the thermal transition. However, Hill numbers showed no response to temperature when rare morphotypes were emphasized (order q = 0) or a weak response when they were balanced with common morphotypes (order q = 1). Hill number of order q = 2, emphasizing the most common morphotypes, consistently increased with temperature
across different sample sizes or coverages. This illustrates how common morphotypes, rather than the rare ones, may boost biodiversity facing warming.
2. We analysed the distribution of aquatic beetles (Coleoptera, Dytisicidae, including the genera Agabus, Platambus, Hydroporus and Boreonectes) in a set of 82 lakes in the Pyrenees. Temperature was the most important variable explaining the overall distribution of dytiscids (out of 29 environmental variables considered). The presence of fish (i.e. salmonids) and macrophyte cover (plants provide refuge from predators) was also important. Indeed, either salmonids or macrophytes as single factors explained more of the variance in dytiscid distribution than temperature.
3. Further analysis showed that the presence of salmonids was particularly important for the medium-sized dytiscid Agabus bipustulatus. This species is generally eurythermic, although in the Pyrenees it is found mainly in cold lakes. This is attributed to predation pressure from fish, since the latter are more likely to be present in warm lakes. As a consequence, salmonids increase fragmentation of A. bipustulatus with respect to populations occupying lowland habitats.
4. Predation can therefore constrain the distribution of species to a fraction of habitats that appear suitable based on simple thermal responses. As humans also facilitate the dispersal of non-native fish, the consequent modification of distribution patterns in fresh waters could make it difficult to predict how distributions might change in relation to climate warming.
changed during the thermal transition. However, Hill numbers showed no response to temperature when rare morphotypes were emphasized (order q = 0) or a weak response when they were balanced with common morphotypes (order q = 1). Hill number of order q = 2, emphasizing the most common morphotypes, consistently increased with temperature
across different sample sizes or coverages. This illustrates how common morphotypes, rather than the rare ones, may boost biodiversity facing warming.
2. We analysed the distribution of aquatic beetles (Coleoptera, Dytisicidae, including the genera Agabus, Platambus, Hydroporus and Boreonectes) in a set of 82 lakes in the Pyrenees. Temperature was the most important variable explaining the overall distribution of dytiscids (out of 29 environmental variables considered). The presence of fish (i.e. salmonids) and macrophyte cover (plants provide refuge from predators) was also important. Indeed, either salmonids or macrophytes as single factors explained more of the variance in dytiscid distribution than temperature.
3. Further analysis showed that the presence of salmonids was particularly important for the medium-sized dytiscid Agabus bipustulatus. This species is generally eurythermic, although in the Pyrenees it is found mainly in cold lakes. This is attributed to predation pressure from fish, since the latter are more likely to be present in warm lakes. As a consequence, salmonids increase fragmentation of A. bipustulatus with respect to populations occupying lowland habitats.
4. Predation can therefore constrain the distribution of species to a fraction of habitats that appear suitable based on simple thermal responses. As humans also facilitate the dispersal of non-native fish, the consequent modification of distribution patterns in fresh waters could make it difficult to predict how distributions might change in relation to climate warming.