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Map of drainages sampled in the Northern Range of Trinidad (1 = Marianne, 2 = Arima, 3 = Guanapo, 4 = Aripo, 5 = Quare, 6 = Turure). Top center is detail of Heights of Guanapo from the Guanapo drainage, which contains the 4 focal sites (Lower La Laja = LOL, Upper La Laja = UPL, Taylor = TAY, and Caigual = CAI).
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Light, nutrient availability, and flow are strong factors controlling the elemental composition and biomass of epilithon in temperate stream ecosystems. However, comparatively little is known about these relationships in tropical streams. We investigated how gradients of light and nutrient availability, seasonality, and habitat influenced epilithon...
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... Science jnbs-31-04-01.3d 16/8/12 10: 13:36and biomass in 4 first-order streams in the Guanapo drainage: Lower La Laja (LOL), Upper La Laja (UPL), Taylor (TAY), and Caigual (CAI) (Fig. 1). These 4 headwater streams, collectively termed focal streams, are relatively undisturbed, although they drain small areas of active and inactive citrus, coffee, and cocoa plantations ( Helson et al. 2006) and are similar in geology and floral communities. We sampled streams every other month from September 2007 to September 2009. In ...
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... we surveyed 18 stream sites from 6 river basins in Trinidad's Northern Range (Fig. 1). These streams represented a broad range of natural canopy cover and nutrient concentrations. Thus, we were able to examine the effects of light and nutrients on epilithon biomass and stoichiometry across larger gradients than existed in focal streams. Three of these drainages, the Turure, Quare, and Aripo, have prominent CaCO 3 ...
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... stage, and dissolved nutrients.-Scouring flow events were more frequent during the wet season, with fewer days between events raising stream stage §8 cm (t-test, t = 16.81, p , 0.001) or 16 cm (t-test, t = TABLE 1. Minimum adequate generalized least squares models for epilithon variables in focal streams (see Fig. 1 for stream names). df = degrees of freedom, L-ratio = log likelihood ratio, vf = variance function, AFDM = ash-free dry mass, AI = autotrophic index, SRP = soluble reactive P, since.8 = days since an 8-cm increase in stream stage, since.16 = days since a 16-cm increase in stream stage. . Minimum adequate generalized least squares ...
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... L-ratio = log likelihood ratio, vf = variance function, AFDM = ash-free dry mass, AI = autotrophic index, SRP = soluble reactive P, since.8 = days since an 8-cm increase in stream stage, since.16 = days since a 16-cm increase in stream stage. . Minimum adequate generalized least squares models for epilithon variables in survey streams (see Fig. 1 for drainages). Chlorophyll a, ash-free dry mass (AFDM), and autotrophic index (AI) values from samples collected with Loeb samplers were excluded (see text for explanation). df = degrees of freedom, L-ratio = log likelihood ratio, vf = variance function, SRP = soluble reactive P. (Fig. 2). DIN and SRP concentrations ranged from 76 to ...
Citations
... The carbon to nitrogen (CN) ratio of the high-and low-quality food was measured in a CHNS analyser and determined to be an average of 8.7 and 17.5, respectively. These values are comparable with previously reported CN ratios of invertebrates (high-quality food) and algae (low-quality food) in Trinidadian streams [15,18]. Both food types were similar in appearance and consistency, and only differed in nutrient content. ...
Eco-evolutionary theory has brought an interest in the rapid evolution of functional traits. Among them, diet is an important determinant of ecosystem structure, affecting food web dynamics and nutrient cycling. However, it is largely unknown whether diet, or diet preference, has a hereditary basis and can evolve on contemporary timescales. Here, we study the diet preferences of Trinidadian guppies Poecilia reticulata collected from directly below an introduction site of fish transplanted from a high-predation environment into a low predation site where their densities and competition increased. Behavioural assays on F2 common garden descendants of the ancestral and derived populations showed that diet preference has rapidly evolved in the introduced population in only 12 years (approx. 36 generations). Specifically, we show that the preference for high-quality food generally found in high-predation guppies is lost in the newly derived low-predation population, who show an inertia toward the first encountered food. This result is predicted by theory stating that organisms should evolve less selective diets under higher competition. Demonstrating that diet preference can show rapid and adaptive evolution is important to our understanding of eco-evolutionary feedbacks and the role of evolution in ecosystem dynamics.
... Molluscs are filter feeding benthic organisms widely distributed around the world and perform many important functions in aquatic ecosystems. The importance of molluscs in contribution to food security, employment and economy, especially for the poorer segments of the society is well documented (Balian et al., 2008;Strong et al., 2008;Kohler et al., 2012;Ngor et al., 2018). It is also playing an important role in ecosystem services (Ngor et al., 2018;Vaughn, 2018). ...
Lamellidens marginalis (Lamarck, 1819), is a widely distributed mussel species in India and it is an important bivalve that can be used for the production of pearl. In the present study, L. marginalis were collected from low lying areas around Patna and analysed for length-weight relationship, proximate composition, amino acid concentration and fatty acid profile. Growth study was also conducted for a period of 160 days to record the performance of this species, when reared at subsurface and bottom of a fish pond. The length-weight relationship was found to be Y=3.856X-12.81 and growth coefficient "b" was significantly higher indicating allometric growth pattern. Crude protein, fat, ash and moisture content in the flesh recorded were 7.19, 1.64, 3.70 and 83.92% respectively. Among essential amino acids, lysine was most abundant and low levels of isoleucine was recorded, while among non-essential amino acids, glutamate was dominant. Moreover, 32 fatty acids were recorded in the mussel including omega-3-fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Off-bottom culture in the pond performed better than on-bottom culture. Percentage body weight gain (BWG%) and specific growth rate (SGR%) were also higher for off-bottom grown mussels.
... It is possible that the primary production of streams may vary more widely at higher elevations between the dry and wet seasons, influencing stream fish fecundity. Variable stream flow and discharge affect the flow of nutrients to primary producers, and thus affect the quality and quantity of food for stream fishes (Kohler et al. 2012). Seasonal variation in productivity is still poorly understood in tropical streams. ...
Neoheterandria tridentiger (Garman) is a poeciliid fish endemic to freshwater drainages in
Panamá. This species utilizes superfetation, the carrying of broods of different ages. Life history parameters including incidence of superfetation, number of embryos, and size at maturity are presented for a population of N. tridentiger. Fish were collected in May, 2015, at the end of the dry season from Río Antón in El Valle de Antón in central Panamá at an elevation of 700 m. Female size at maturity was 22 mm SL. 75% of mature females were found to be carrying at least one developing embryo, the mean number of embryos was five, and the mean embryo dry mass was 1.42 mg. Superfetation was found in 23% of gravid females. Earlier research findings from two different populations in August, 1973, during the rainy season found that gravid female size was smaller at (17 mm SL), with superfetation rates of 70% and 80%. Males collected in May, 2015, were 16–27 mm SL, whereas those collected in August, 1973, were 10–16 mm SL. Shifting size and fecundity could be driven by seasonal food web changes affecting both adults and offspring.
... We observed guppy courtship in the Caigual (61.275 • W 10.715 • N) and Taylor (61.271 • W 10.708 • N) tributaries of the Guanapo river in the northern range of Trinidad, which have elevations of 297 and 281 m, respectively. These are shallow streams in rainforest less than 1 km apart and are typical of guppy populations at higher elevations in the Northern Range Mountains [29]. Locations and sample sites were chosen with habitats and microhabitats as similar as possible, shaded at the time of observations, as well as a locally higher guppy density to ensure good sample sizes. ...
... In addition, the greenish light of FS results in less total guppy reflectance (brightness) for a given total irradiance compared to OC, reducing visibility further. The relative difference in light usage is probably not due to availability, because Taylor has a relatively more open canopy than Caigual due to experimental canopy thinning [29]. Relative availability depends upon the size of canopy gaps [31]. ...
Male guppies (Poecilia reticulata) have multiple colored spots and perform courtship displays near the edges of streams in Trinidad in shallow water flowing through rainforest. Depending upon the orientation of the pair, the female sees the male displays against gravel or other stream bed substrates or against the spacelight—the roughly uniform light coming from the water column away from the bank. We observed courting pairs in two adjacent natural streams and noted the directions of each male display. We found that the female sees the male more often against spacelight than against gravel when females either faced the spacelight from the opposite bank or from downstream, or both. Visual modelling using natural substrate reflectances and field light measurements showed higher chromatic contrast of males against spacelight than against substrates independent of the two ambient light environments used during displays, but achromatic contrast depended upon the ambient light habitat. This suggests that courtship involves both chromatic and achromatic contrast. We conclude that the orientation of courting pairs and the ambient light spectrum should be accounted for in studies of mate choice, because the visual background and light affect visibility, and these differ with orientation.
... Specifically, we assessed how reproduction scaled with female body size (a) for different measures of reproductive output both in the wild and laboratory, (b) for wild fish sampled either in the dry or (resource-poor) wet season and (c) for laboratory-reared fish fed either a high-quantity or low-quantity diet. During the wet season in Trinidad, increased water flow and flooding scours the streams of the invertebrates, algae, and detritus that guppies feed on, leading to more intense competition for resources (Kohler et al., 2012;Zandonà et al., 2015). In the laboratory, ...
In wild populations, large individuals have disproportionately higher reproductive output than smaller individuals. Some theoretical models explain this pattern—termed reproductive hyperallometry—by individuals allocating a greater fraction of available energy towards reproductive effort as they grow.
Here, we propose a simple ecological explanation for this observation: differences between individuals in rates of resource assimilation, where greater assimilation causes both increased reproduction and body size, resulting in reproductive hyperallometry at the level of the population.
We illustrate this effect by determining the relationship between size and reproduction in wild and laboratory‐reared Trinidadian guppies. We show that (a) reproduction increased disproportionately with body size in the wild but not in the laboratory, where resource competition was eliminated; (b) in the wild, hyperallometry was greatest during the wet season, when resource competition is strongest; and (c) detection of hyperallometric scaling of reproduction at the population level was inevitable if individual differences in assimilation were ignored.
We propose that ecologically driven variation in assimilation—caused by size‐dependent resource competition, niche expansion and chance—contributes substantially to observations of hyperallometric scaling of reproduction in natural populations. We recommend that models incorporate such ecologically caused variation when seeking to explain reproductive hyperallometry.
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... Due to their roughness, stones provide a three-dimensional habitat that protects microphytes from various disturbances and grazers (Bergey, 2008 and references therein). The development and composition of epilithic communities is highly dependent on light, nutrients, and flow regime (Francoeur et al., 1998;Kohler et al., 2012). In a highly turbulent river environment, the epilithon consist mainly of diatoms, which are adapted to poor light conditions and are firmly attached to the substrate (Zelnik and Sušin, 2020), making them less available to other communities. ...
To study the early colonization processes, polyethylene terephthalate (PET) microfragments were immersed in Lake Sakadaš and the Drava River and sampled weekly together with the surrounding biotic communities - phytoplankton, zooplankton, epixylon in the lake and epilithon in the river. At the end of the study, a rise in water level occurred in the river, which altered the environmental conditions and plankton communities. In studied environments, all of the sampled biotic communities were diverse and abundant. Plastispheres formed in both waters by the seventh day of incubation and developed rapidly, reaching a peak in abundance on the last day of the study. Initial colonization was supported equally by planktonic and periphytic taxa in both environments, but after initial settlement, plastisphere assemblages were affected differently in the river and lake. This study suggests that PET microfragments are a suitable substrate for microphyte settlement and may provide an important pathway for their transport in dynamic freshwater floodplains and river systems.
... ILL and IUL were introduced with much lower initial population densities due to fewer introduced fish and larger stream size than either IC and IT. IUL and IT had artificially thinned tree canopies (Fig. 1), which increased primary productivity (Kohler et al. 2012). Natural barriers restrict migration into the experimental populations. ...
Although rapid phenotypic evolution has been documented often, the genomic basis of rapid adaptation to natural environments is largely unknown in multicellular organisms. Population genomic studies of experimental populations of Trinidadian guppies (Poecilia reticulata) provide a unique opportunity to study this phenomenon. Guppy populations that were transplanted from high‐predation (HP) to low‐predation (LP) environments have been shown to evolve toward the phenotypes of naturally colonized LP populations in as few as eight generations. These changes persist in common garden experiments, indicating that they have a genetic basis. Here, we report results of whole genome variation in four experimental populations colonizing LP sites along with the corresponding HP source population. We examined genome‐wide patterns of genetic variation to estimate past demography and used a combination of genome scans, forward simulations, and a novel analysis of allele frequency change vectors to uncover the signature of selection. We detected clear signals of population growth and bottlenecks at the genome‐wide level that matched the known history of population numbers. We found a region on chromosome 15 under strong selection in three of the four populations and with our multivariate approach revealing subtle parallel changes in allele frequency in all four populations across this region. Investigating patterns of genome‐wide selection in this uniquely replicated experiment offers remarkable insight into the mechanisms underlying rapid adaptation, providing a basis for comparison with other species and populations experiencing rapidly changing environments.
... The low turbidity and water discharge, high residence times, and higher water temperatures favor algal development in the lower Usumacinta basin sampling sites. Other tropical rivers have higher algal growth under these environmental conditions during the drier stages [72]. Primary production in floodplains or lentic-like environments also enhances autochthonous organic matter inputs to the rivers [73]; for instance, the lower-basin floodplains of the Orinoco River display nutrient-rich waters fostering higher algal contributions [74]. ...
Particulate organic carbon (POC) derived from inland water plays an important role in the global carbon (C) cycle; however, the POC dynamic in tropical rivers is poorly known. We assessed the POC concentration, flux, and sources in the Usumacinta, the largest tropical river in North America, to determine the controls on POC export to the Gulf of Mexico. We examined the Mexican middle and lower Usumacinta Basin during the 2017 dry (DS) and rainy (RS) seasons. The POC concentration ranged from 0.48 to 4.7 mg L−1 and was higher in the RS, though only in the middle basin, while remaining similar in both seasons in the lower basin. The POC was predominantly allochthonous (54.7 to 99.6%). However, autochthonous POC (phytoplankton) increased in the DS (from 5.1 to 17.7%) in both basins. The POC mass inflow–outflow balance suggested that floodplains supply (C source) autochthonous POC during the DS while retaining (C sink) allochthonous POC in the RS. Ranging between 109.1 (DS) and 926.1 t POC d−1 (RS), the Usumacinta River POC export to the Gulf of Mexico was similar to that of other tropical rivers with a comparable water discharge. The extensive floodplains and the “Pantanos de Centla” wetlands in the lowlands largely influenced the POC dynamics and export to the southern Gulf of Mexico.
... In the other two streams (LL and CA), we left the dense canopy intact. Previous assessment revealed substantial differences in light availability resulting from thinning the forest canopy (Kohler et al. 2012). Natural barrier waterfalls divided all four study streams into two distinct sections: a downstream guppy introduction reach (i.e., introduction) and an upstream killifish-only (i.e., reference). ...
... We recorded light intensity every 30 min with Onset HOBO temperature/light loggers (Onset Instruments, Bourne, MA, USA) attached one meter above streambed, approximately 10 m apart. Light intensity was transformed into instantaneous photosynthetically active radiation (PAR), determined by integrating the 30-min readings for each day (Kohler et al. 2012). ...
... Across streams and experimental treatments (i.e., open or closed canopy sites), there was substantial variation in all measured parameters (Fig. 4). This may well be explained by intervals of flooding which can reduce the standing crop of algae by five-to ten-fold (Kohler et al. 2012), the abundance of invertebrates by up to a thousandfold (Heatherly 2012) and the abundance of guppies by up to sevenfold (Travis et al. 2014). This may explain why stage had an effect on GPP and CR. ...
The ecological consequences of biological range extensions reflect the interplay between the functional characteristics of the newly arrived species and their recipient ecosystems. Teasing apart the relative contribution of each component is difficult because most colonization events are studied retrospectively, i.e., after a species became established and its consequences apparent. We conducted a prospective experiment to study the ecosystem consequences of a consumer introduction, using whole-stream metabolism as our integrator of ecosystem activity. In four Trinidadian streams, we extended the range of a native fish, the guppy (Poecilia reticulata), by introducing it over barrier waterfalls that historically excluded it from these upper reaches. To assess the context dependence of these range extensions, we thinned the riparian forest canopy on two of these streams to increase benthic algal biomass and productivity. Guppy's range extension into upper stream reaches significantly impacted stream metabolism but the effects depended upon the specific stream into which they had been introduced. Generally, increases in guppy biomass caused an increase in gross primary production (GPP) and community respiration (CR). The effects guppies had on GPP were similar to those induced by increased light level and were larger in strength than the effects stream stage had on CR. These results, combined with results from prior experiments, contribute to our growing understanding of how consumers impact stream ecosystem function when they expand their range into novel habitats. Further study will reveal whether local adaptation, known to occur rapidly in these guppy populations, modifies the ecological consequences of this species introduction.
... Generally, autochthonous resources such as benthic algae are a higher quality food resource than allochthonous detritus because the N and P content of living plant material tends to be higher than that of detrital leaves and wood (Evans-White et al., 2005;McManamay et al., 2011). Previous work has indicated that light, nutrient availability, and flow interactively affect both water column and benthic algal stoichiometry Kohler et al., 2012). Specifically, enhanced nutrient availability decreases C: nutrient ratios while light increases C:nutrient ratios Sanches et al., 2011), and variation in flow impacts stoichiometry of primary producers by shaping algal community structure and influencing nutrient flux (Dodds and Biggs, 2002;Francoeur and Biggs, 2006). ...
Ecological stoichiometry (ES) is the study of how the availability of multiple elements, including carbon, nitrogen, and phosphorus, constrain ecological interactions. Since its inception, ES has provided an integrative framework to advance the science of stream ecology across organismal to ecosystem levels. Here, we review principles of ES in streams, focusing on homeostatic regulation among stream organisms, patterns of elemental imbalances within stream food webs, and scaling from organismal processes to community and ecosystem levels using the concept of consumer-driven nutrient dynamics. We close with a list of knowledge gaps and future directions for ES to continue advancing stream ecology.
