Traits across trophic levels interact to influence parasitoid establishment in biological control releases

A central goal in ecology is to predict what governs a species’ ability to establish in a new environment. One mechanism driving establishment success is individual species’ traits, but the role of trait combinations among interacting species across different trophic levels is less clear. Deliberate or accidental species additions to existing communities provide opportunities to study larger scale patterns of establishment success. Biological control introductions are especially valuable because they contain data on both the successfully established and unestablished species. Here, we used a recent dataset of importation biological control introductions to explore how life‐history traits of 132 parasitoid species and their herbivorous hosts interact to affect parasitoid establishment. We find that of five parasitoid and herbivore traits investigated, one parasitoid trait—host range—weakly predicts parasitoid establishment; parasitoids with higher levels of phylogenetic specialization have higher establishment success, though the effect is marginal. In addition, parasitoids are more likely to establish when their herbivore host has had a shorter residence time. Interestingly, we do not corroborate earlier findings that gregarious parasitoids and endoparasitoids are more likely to establish. Most importantly, we find that life‐history traits of the parasitoid species and their hosts can interact to influence establishment. Specifically, parasitoids with broader host ranges are more likely to establish when the herbivore they have been released to control is also more of a generalist. These results provide insight into how multiple species’ traits and their interactions, both within and across trophic levels, can influence establishment of species of higher trophic levels.     

黄河上游甘蒙柽柳生长对极端旱涝的响应

青藏高原黄河上游河岸带是典型的生态脆弱区, 然而近年来气候变暖加剧了该地极端旱涝事件的频繁发生, 高原河岸带生态脆弱区植被是否能够应对极端旱涝事件的干扰成为流域生态环境管理工作所关注的重点问题。为了研究黄河上游河岸林中主要树种对极端旱涝的响应, 该研究选取青海省同德县和兴海县3处河岸林中的47株甘蒙柽柳(Tamarix austromongolica), 分别从树干面向邻近山体一侧及与之垂直的一侧分别获取1根树轮样本, 分析其历史生长。通过对比两个方向上的生长速率判断甘蒙柽柳是否受到地质灾害影响从而将其划分为受伤组和对照组, 分析两组甘蒙柽柳在过去63年中径流极值年的抵抗力状况及两个方向的生长差异。研究发现, 甘蒙柽柳对干旱和洪涝均有着很强的抵抗力, 河岸带多样化的水分来源有助于甘蒙柽柳在极端干旱环境中较好地生长; 但洪涝伴随泥石流等地质灾害的频发使甘蒙柽柳面向山体侧面受到严重的生长抑制, 表现出显著的方向性差异, 从而影响甘蒙柽柳的形态。较长的创伤恢复期带来的遗留效应可能造成甘蒙柽柳对外界干扰的较高敏感性。研究黄河上游甘蒙柽柳生长对极端旱涝的响应, 将有助于评估生态脆弱区生态弹性过程, 同时为高原河岸带生态建设和恢复提供科学依据。     

Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra‐annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.     

Elevational Ranges of Montane Birds and Deforestation in the Western Andes of Colombia

Deforestation causes habitat loss, fragmentation, degradation, and can ultimately cause extinction of the remnant species. Tropical montane birds face these threats with the added natural vulnerability of narrower elevational ranges and higher specialization than lowland species. Recent studies assess the impact of present and future global climate change on species’ ranges, but only a few of these evaluate the potentially confounding effect of lowland deforestation on species elevational distributions. In the Western Andes of Colombia, an important biodiversity hotspot, we evaluated the effects of deforestation on the elevational ranges of montane birds along altitudinal transects. Using point counts and mist-nets, we surveyed six altitudinal transects spanning 2200 to 2800m. Three transects were forested from 2200 to 2800m, and three were partially deforested with forest cover only above 2400m. We compared abundance-weighted mean elevation, minimum elevation, and elevational range width. In addition to analysing the effect of deforestation on 134 species, we tested its impact within trophic guilds and habitat preference groups. Abundance-weighted mean and minimum elevations were not significantly different between forested and partially deforested transects. Range width was marginally different: as expected, ranges were larger in forested transects. Species in different trophic guilds and habitat preference categories showed different trends. These results suggest that deforestation may affect species’ elevational ranges, even within the forest that remains. Climate change will likely exacerbate harmful impacts of deforestation on species’ elevational distributions. Future conservation strategies need to account for this by protecting connected forest tracts across a wide range of elevations.     

Current Analogues of Future Climate Indicate the Likely Response of a Sensitive Montane Tropical Avifauna to a Warming World

Among birds, tropical montane species are likely to be among the most vulnerable to climate change, yet little is known about how climate drives their distributions, nor how to predict their likely responses to temperature increases. Correlative models of species’ environmental niches have been widely used to predict changes in distribution, but direct tests of the relationship between key variables, such as temperature, and species’ actual distributions are few. In the absence of historical data with which to compare observations and detect shifts, space-for-time substitutions, where warmer locations are used as analogues of future conditions, offer an opportunity to test for species’ responses to climate. We collected density data for rainforest birds across elevational gradients in northern and southern subregions within the Australian Wet Tropics (AWT). Using environmental optima calculated from elevational density profiles, we detected a significant elevational difference between the two regions in ten of 26 species. More species showed a positive (19 spp.) than negative (7 spp.) displacement, with a median difference of ∼80.6 m across the species analysed that is concordant with that expected due to latitudinal temperature differences (∼75.5 m). Models of temperature gradients derived from broad-scale climate surfaces showed comparable performance to those based on in-situ measurements, suggesting the former is sufficient for modeling impacts. These findings not only confirm temperature as an important factor driving elevational distributions of these species, but also suggest species will shift upslope to track their preferred environmental conditions. Our approach uses optima calculated from elevational density profiles, offering a data-efficient alternative to distribution limits for gauging climate constraints, and is sensitive enough to detect distribution shifts in this avifauna in response to temperature changes of as little as 0.4 degrees. We foresee important applications in the urgent task of detecting and monitoring impacts of climate change on montane tropical biodiversity.     

Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate‐driven hydrological change along the Vindel River in Sweden

1. Riparian plant communities are primarily structured by the hydrological regime of the stream. Models of climate change predict increased temperatures and changed patterns of precipitation that will alter the flow of rivers and streams with consequences for riparian communities. In boreal regions of Europe, stream flows will exhibit earlier spring‐flood peaks of lower magnitude, lower summer flows and higher flows in autumn and winter. We quantified the effects of predicted hydrological change on riparian plant species richness, using four different scenarios for the free‐flowing Vindel River in northern Sweden. 2. We calculated the hydrological niche of vegetation belts by relating the occurrence of species and vegetation belts to data on flood duration for 10 years preceding the vegetation survey. We then used the flood duration predicted for 2071–2100 to estimate expected changes in the extent of each vegetation belt. Using species accumulation curves, we then predicted changes in plant species richness as a result of changes in extent. 3. The two most species‐rich vegetation belts, riparian forest and willow shrub, were predicted to decrease most in elevational extent, up to 39 and 32%, respectively. The graminoid belt below the shrub belt will mainly shift upwards in elevation while the amphibious vegetation belt at the bottom of the riparian zone increases in size. 4. In the Vindel River, the riparian forest and willow shrub zone will lose most species, with reductions of 5–12% and 1–13% per site, respectively, depending on the scenario. The predicted loss from the entire riparian zone is lower, 1–9%, since many species occur in more than one vegetation belt. More extensive species losses are expected in the southern boreal zone for which much larger spring‐flood reductions are projected. 5. With an expected reduction in area of the most species‐rich belts, it becomes increasingly important to manage and protect riparian zones to alleviate other threats, thus minimising the risk of species losses. Restoring river and stream reaches degraded by other impacts to gain riparian habitat is another option to avoid species losses.     

Comparing the fish assemblages and food‐web structures of large floodplain rivers

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Large-scale multi-trophic co-response models and environmental control of pelagic food webs in Québec lakes

Environmental heterogeneity plays a fundamental role in driving species distributions by, for one, fostering niche dimensionality. Within lake ecosystems, species distributions and concordance patterns are driven by both local and regional heterogeneity, though their relative importance across trophic levels has rarely been explored. We developed a statistical framework to compare responses of taxa from different trophic levels to abiotic factors and determine how this affected multi-trophic network structures. In particular, we used multi-species concordance modelling (concordance analysis and RV coefficient) to determine species associations and correlations within and among three trophic levels (phytoplankton, zooplankton and fish communities sampled across 49 southern Québec lakes, covering eight hydrological regions). We then used multiple factor analysis, latent variable modelling and local contributions of sites to beta diversity to assess the relative importance of major environmental gradients in structuring species co-responses and species interaction turnover across the landscape. Our analyses confirmed that concordant species within each trophic level varied jointly or segregated into different pelagic food webs in Québec lakes where important acidification and eutrophication took place. Some keynote species were indicators of different food web compartments and distinguished groups of lakes along multiple environmental niche dimensions. Among the three trophic levels examined, zooplankton depicted the highest proportion of species concordance and appeared to act as a trophic linkage between phytoplankton and fish. Ultimately, the losses or gains in species richness and species interactions were strongly driven by environmental gradients. This study provides for the first time a combined analysis of the effects of environmental heterogeneity on ecological communities belonging to three trophic levels sampled near simultaneously across an 800 km broad lacustrine landscape. The new framework developed in this study has a great potential to better understand the complex response of aquatic ecosystems in a world increasingly affected by multiple, cumulative stressors.     

Signals of Climate Change in Butterfly Communities in a Mediterranean Protected Area

The European protected-area network will cease to be efficient for biodiversity conservation, particularly in the Mediterranean region, if species are driven out of protected areas by climate warming. Yet, no empirical evidence of how climate change influences ecological communities in Mediterranean nature reserves really exists. Here, we examine long-term (1998–2011/2012) and short-term (2011–2012) changes in the butterfly fauna of Dadia National Park (Greece) by revisiting 21 and 18 transects in 2011 and 2012 respectively, that were initially surveyed in 1998. We evaluate the temperature trend for the study area for a 22-year-period (1990–2012) in which all three butterfly surveys are included. We also assess changes in community composition and species richness in butterfly communities using information on (a) species’ elevational distributions in Greece and (b) Community Temperature Index (calculated from the average temperature of species'' geographical ranges in Europe, weighted by species'' abundance per transect and year). Despite the protected status of Dadia NP and the subsequent stability of land use regimes, we found a marked change in butterfly community composition over a 13 year period, concomitant with an increase of annual average temperature of 0.95°C. Our analysis gave no evidence of significant year-to-year (2011–2012) variability in butterfly community composition, suggesting that the community composition change we recorded is likely the consequence of long-term environmental change, such as climate warming. We observe an increased abundance of low-elevation species whereas species mainly occurring at higher elevations in the region declined. The Community Temperature Index was found to increase in all habitats except agricultural areas. If equivalent changes occur in other protected areas and taxonomic groups across Mediterranean Europe, new conservation options and approaches for increasing species’ resilience may have to be devised.     

A Landscape-Scale,Applied Fire Management Experiment Promotes Recovery of a Population of the Threatened Gouldian Finch,Erythrura gouldiae,in Australia’s Tropical Savannas

Fire is an integral part of savanna ecology and changes in fire patterns are linked to biodiversity loss in savannas worldwide. In Australia, changed fire regimes are implicated in the contemporary declines of small mammals, riparian species, obligate-seeding plants and grass seed-eating birds. Translating this knowledge into management to recover threatened species has proved elusive. We report here on a landscape-scale experiment carried out by the Australian Wildlife Conservancy (AWC) on Mornington Wildlife Sanctuary in northwest Australia. The experiment was designed to understand the response of a key savanna bird guild to fire, and to use that information to manage fire with the aim of recovering a threatened species population. We compared condition indices among three seed-eating bird species–one endangered (Gouldian finch) and two non-threatened (long-tailed finch and double-barred finch)—from two large areas (> 2,830 km²) with initial contrasting fire regimes (‘extreme’: frequent, extensive, intense fire; versus ‘benign’: less frequent, smaller, lower intensity fires). Populations of all three species living with the extreme fire regime had condition indices that differed from their counterparts living with the benign fire regime, including higher haematocrit levels in some seasons (suggesting higher levels of activity required to find food), different seasonal haematocrit profiles, higher fat scores in the early wet season (suggesting greater food uncertainty), and then lower muscle scores later in the wet season (suggesting prolonged food deprivation). Gouldian finches also showed seasonally increasing stress hormone concentrations with the extreme fire regime. Cumulatively, these patterns indicated greater nutritional stress over many months for seed-eating birds exposed to extreme fire regimes. We tested these relationships by monitoring finch condition over the following years, as AWC implemented fire management to produce the ‘benign’ fire regime throughout the property. The condition indices of finch populations originally living with the extreme fire regime shifted to resemble those of their counterparts living with the benign fire regime. This research supports the hypothesis that fire regimes affect food resources for savanna seed-eating birds, with this impact mediated through a range of grass species utilised by the birds over different seasons, and that fire management can effectively moderate that impact. This work provides a rare example of applied research supporting the recovery of a population of a threatened species.     

Environment‐driven changes in diversity of riparian plant communities along a mountain river

The study of changes in species richness and composition along rivers has focused on large spatial scales. It has been ignored that in different sections of the river (high mountain area, middle zone, and mouth of the river) the specific environmental conditions can generate different longitudinal patterns of the species richness and composition. In this study, we determine whether species richness and composition of the riparian plant communities change along a mountain river and whether these changes are related to environmental variables. We expect an increase in species richness and turnover along the river, that the upstream communities would be a subset of the downstream communities, and that such would be related to edaphic and hydrologic conditions. To test this, we sampled three strata of the riparian vegetation (upper: individuals with <1 cm of ND, middle: individuals with >1 cm of ND, low: individuals with >1 m tall) in a set of 15 sites that we place along a mountain river. Additionally, we recorded topographic, hydrological, morphological, and soil variables. We performed correlation analyzes to determine whether changes in species richness and turnover were related to increased distance to the origin of the river. Also, we obtained the nestedness and evaluated the importance of environmental variables with GLM, LASSO regression, and CCA. With the increase in distance, the species richness decreases in the upper stratum, but not in the middle and the low stratum (although the highest values were observed near the origin of the river), the turnover increase in all strata and the upstream communities were not a subset of the downstream communities. The changes in species richness and composition were related to topographic (altitude), hydrological (flow), and edaphic (conductivity and pH) variables. Our results indicate that at small spatial scales the patterns of richness and composition differ from what has been found at larger spatial scales and that these patterns are associated with environmental changes in the strong altitude gradients of mountain rivers.     

Interspecific trait variability and local soil conditions modulate grassland model community responses to climate

Medium‐to‐high elevation grasslands provide critical services in agriculture and ecosystem stabilization, through high biodiversity and providing food for wildlife. However, these ecosystems face elevated risks of disruption due to predicted soil and climate changes. Separating the effects of soil and climate, however, is difficult in situ, with previous experiments focusing largely on monocultures instead of natural grassland communities. We experimentally exposed model grassland communities, comprised of three species grown on either local or reference soil, to varied climatic environments along an elevational gradient in the European Alps, measuring the effects on species and community traits. Although species‐specific biomass varied across soil and climate, species'' proportional contributions to community‐level biomass production remained consistent. Where species experienced low survivorship, species‐level biomass production was maintained through increased productivity of surviving individuals; however, maximum species‐level biomass was obtained under high survivorship. Species responded directionally to climatic variation, spatially separating differentially by plant traits (including height, reproduction, biomass, survival, leaf dry weight, and leaf area) consistently across all climates. Local soil variation drove stochastic trait responses across all species, with high levels of interactions occurring between site and species. This soil variability obscured climate‐driven responses: we recorded no directional trait responses for soil‐corrected traits like observed for climate‐corrected traits. Our species‐based approach contributes to our understanding of grassland community stabilization and suggests that these communities show some stability under climatic variation.     

Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions

Climate change is expected to alter the magnitude and variation of flow in streams and rivers, hence providing new conditions for riverine communities. We evaluated plant ecological responses to climate change by transplanting turfs of riparian vegetation to new elevations in the riparian zone, thus simulating expected changes in water‐level variation, and monitored the results over 6 years. Turfs moved to higher elevations decreased in biomass and increased in species richness, whereas turfs transplanted to lower elevations gained biomass but lost species. Transplanted plant communities responded slowly to the new hydrologic conditions. After 6 years, biomass of transplanted turfs was statistically indistinguishable from target level controls, but species richness and species composition of transplants were intermediate between original and target levels. By using projections of future stream flow according to IPCC climate change scenarios, we predict likely changes to riparian vegetation in boreal rivers. Climate‐driven hydrologic changes are predicted to result in narrower riparian zones along the studied Vindel River in northern Sweden towards the end of the 21st century. Present riparian plant communities are projected to be replaced by terrestrial communities at high elevations as a result of lower‐magnitude spring floods, and by amphibious or aquatic communities at low elevations as a result of higher autumn and winter flows. Changes to riparian vegetation may be larger in other boreal climate regions: snow melt fed spring floods are predicted to disappear in southern parts of the boreal zone, which would result in considerable loss of riparian habitat. Our study emphasizes the importance of long‐term ecological field experiments given that plant communities often respond slowly and in a nonlinear fashion to external pressures.     

Community assembly,functional traits,and phylogeny in Himalayan river birds

Heterogeneity in riverine habitats acts as a template for species evolution that influences river communities at different spatio‐temporal scales. Although birds are conspicuous elements of these communities, the roles of phylogeny, functional traits, and habitat character in their niche use or species'' assembly have seldom been investigated. We explored these themes by surveying multiple headwaters over 3000 m of elevation in the Himalayan Mountains of India where the specialist birds of montane rivers reach their greatest diversity on Earth. After ordinating community composition, species traits, and habitat character, we investigated whether river bird traits varied with elevation in ways that were constrained or independent of phylogeny, hypothesizing that trait patterns reflect environmental filtering. Community composition and trait representation varied strongly with increasing elevation and river naturalness as species that foraged in the river/riparian ecotone gave way to small insectivores with direct trophic dependence on the river or its immediate channel. These trends were influenced strongly by phylogeny as communities became more clustered by functional traits at a higher elevation. Phylogenetic signals varied among traits, however, and were reflected in body mass, bill size, and tarsus length more than in body size, tail length, and breeding strategy. These variations imply that community assembly in high‐altitude river birds reflects a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche‐based moulding of trait character. We suggest that the regional co‐existence of river birds in the Himalaya is facilitated by this same array of factors that together reflect the highly heterogeneous template of river habitats provided by these mountain headwaters.     

Importance of scale,land‐use,and stream network properties for riparian plant communities along an urban gradient

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Consistent trophic patterns among fishes in lagoon and channel habitats of a tropical floodplain river: Evidence from stable isotopes

The relationship between food web dynamics and hydrological connectivity in rivers should be strongly influenced by annual flood pulses that affect primary production dynamics and movement of organic matter and consumer taxa. We sampled basal production sources and fishes from connected lagoons and the main channel of a low-gradient, floodplain river within the Orinoco River Basin in Venezuela. Stable isotope analysis was used to model the contribution of four basal production sources to fishes, and to examine patterns of mean trophic position during the falling-water period of the annual flood cycle. IsoSource, a multi-source mixing model, indicated that proportional contributions from production sources to fish assemblages were similar in lagoons and the main channel. Although distributions differed, the means for trophic positions of fish assemblages as well as individual species were similar between the two habitats. These findings contradict recent food web studies conducted in temperate floodplain rivers that described significant differences in trophic positions of fishes from slackwater and floodplain versus main channel habitats. Low between-habitat trophic variation in this tropical river probably results from an extended annual flood pulse (ca. 5 mo.) that allows mixing of sestonic and allochthonous basal production sources and extensive lateral movements of fishes throughout the riverscape.     

Community assembly, stability and signatures of dynamical constraints on food web structure

To understand the dynamics of natural species communities, a major challenge is to quantify the relationship between their assembly, stability, and underlying food web structure. To this end, two complementary aspects of food web structure can be related to community stability: sign structure, which refers to the distributions of trophic links irrespective of interaction strengths, and interaction strength structure, which refers to the distributions of interaction strengths with or without consideration of sign structure. In this paper, using data from a set of relatively well documented community food webs, I show that natural communities generally exhibit a sign structure that renders their stability sensitive to interaction strengths. Using a Lotka-Volterra type population dynamical model, I then show that in such communities, individual consumer species with high values of a measure of their total biomass acquisition rate, which I term “weighted generality”, tend to undermine community stability. Thus consumer species’ trophic modules (a species and all its resource links) should be “selected” through repeated immigrations and extinctions during assembly into configurations that increase the probability of stable coexistence within the constraints of the community's trophic sign structure. The presence of such constraints can be detected by the incidence and strength of certain non-random structural characteristics. These structural signatures of dynamical constraints are readily measurable, and can be used to gauge the importance of interaction-driven dynamical constraints on communities during and after assembly in natural communities.     

Ecological Niche Transferability Using Invasive Species as a Case Study

Species distribution modeling is widely applied to predict invasive species distributions and species range shifts under climate change. Accurate predictions depend upon meeting the assumption that ecological niches are conserved, i.e., spatially or temporally transferable. Here we present a multi-taxon comparative analysis of niche conservatism using biological invasion events well documented in natural history museum collections. Our goal is to assess spatial transferability of the climatic niche of a range of noxious terrestrial invasive species using two complementary approaches. First we compare species’ native versus invasive ranges in environmental space using two distinct methods, Principal Components Analysis and Mahalanobis distance. Second we compare species’ native versus invaded ranges in geographic space as estimated using the species distribution modeling technique Maxent and the comparative index Hellinger’s I. We find that species exhibit a range of responses, from almost complete transferability, in which the invaded niches completely overlap with the native niches, to a complete dissociation between native and invaded ranges. Intermediate responses included expansion of dimension attributable to either temperature or precipitation derived variables, as well as niche expansion in multiple dimensions. We conclude that the ecological niche in the native range is generally a poor predictor of invaded range and, by analogy, the ecological niche may be a poor predictor of range shifts under climate change. We suggest that assessing dimensions of niche transferability prior to standard species distribution modeling may improve the understanding of species’ dynamics in the invaded range.     

Seed dispersal by rivers in tropical dry forests: An overlooked process in tropical central Mexico

Aims

Rivers are important corridors for the movement, migration and dispersal of aquatic organisms, including seeds from riparian plants. Although tropical dry forests (TDF) are among the most extensive and floristically rich ecosystems of tropical habitats, and the most globally endangered ecosystem, less attention has been given to riparian corridors within this ecosystem. Although most TDFs manifest peak seed dispersal during dry seasons, we hypothesized that riparian corridors may show a dispersal peak during the rainy season, due to an anticipated ‘sweep or drag effect’, resulting from river overflow and bank erosion. Our main aims were to investigate whether there were any differences in the seed communities transported by the river to sites in rainy as opposed to dry seasons, and to evaluate any possible relationship between the riparian seed community and river flow.

Location

Amacuzac River, drainage of the Balsas basin, State of Morelos, Mexico.

Methods

To evaluate the above assumption, we associated Amacuzac River flow with the number of species and seeds dispersed by water. We also characterized and evaluated differences between seed communities transported by the river during the rainy and dry seasons, and between four different sites located along the river. We used univariate and ordination NMDS techniques to evaluate patterns between seasons at the community level.

Results

Forty‐five plant species were identified from 909 seeds collected from the river. The composition of riparian seed communities was markedly different between seasons but not between sites. Seed abundances were significantly higher in the rainy than in the dry season and varied between sites. Seed species diversity in the river (H’ = 1.6–1.9) showed no significant differences between seasons or sites, but species assemblages and dominance varied according to season. Ordination techniques and subsequent fitting analyses showed that seed species composition was positively associated with river flow.

Conclusions

Seed dispersal patterns generated by rivers are significant mechanisms for structuring the composition and distribution of the riparian plant community in Mexican TDF. Varying species assemblages and seed abundance dispersed by the river throughout the year is a relevant and until now unknown consequence that may affect the dynamics and composition of riparian plant communities in this region. This study initiative will promote new avenues of research regarding plant establishment and succession.