Abstract: Riverine ecosystems are linked to their watersheds, and both land use and physiographic... more Abstract: Riverine ecosystems are linked to their watersheds, and both land use and physiographic environmental
conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship
with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas,
USA) to examine the interactions between land use and physiography and their combined influences on riverine
nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients
explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively).
The response of nutrient concentrations to spatial patterns of land use and physiography depended
on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were
associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the
catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality
and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients,
whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on
dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients
when studying the interactions between a river and its watershed, especially in large, complex watersheds or those
that cross steep environmental gradients.
Background/Question/Methods In order to understand biodiversity-ecosystem functioning relationshi... more Background/Question/Methods In order to understand biodiversity-ecosystem functioning relationship, we examined effects of riparian vegetation diversity on leaf litter decomposition in a stream. Because terrestrial leaf-litter is the dominant energy source to many streams, riparian vegetation diversity can have profound influence on streams ecosystems, which are impacted by human watershed disturbances, including species losses and non-native species introduction. If introduced tree species influences biodiversity-ecosystem functioning relationship in streams is largely unknown. The objective of this study is to assess the effects of tree species diversity (five native riparian species and one introduced species) on leaf litter breakdown in a stream. We conducted a field experiment over 56 days in Barton Creek (Central Texas) to examine temporal patterns of litter breakdown and to detect any non-additive effects of litter diversity on decomposition. The 12 treatments of leaf-bags we...
Light pollution can reduce night time drift of larval aquatic insects in urban streams by disrupt... more Light pollution can reduce night time drift of larval aquatic insects in urban streams by disrupting their circadian rhythms. Previous studies on larval insect drift show that disruption in drift leads to changes in reproduction as well as intraspecific and interspecific interactions. The purpose of this study was to conduct a preliminary investigation into the effects of extreme artificial light on insect drift in urbanized, high clarity spring systems of the karst Edwards Plateau, TX. We quantified taxa richness, diversity, and abundance in aquatic insect night time drift under two treatments (ambient night time light and artificial light addition) and among five streams using a paired design. Richness and diversity of drifting aquatic insects were similar between treatments but abundance was 37% less in the light addition treatment than that of the control. Effects of light addition on mean abundance was more notable in large streams with a 58% decrease in Simuliidae (compared to that of the control) and 51% decrease in Baetidae. Reduced drift from light addition suggests the potential of artificial lighting disrupting insect drift and consequently community structure. Results of this experiment support a growing body of knowledge on how urbanized systems influence stream communities.
Riverine ecosystems are linked to their watersheds, and both land use and physiographic environme... more Riverine ecosystems are linked to their watersheds, and both land use and physiographic environmental conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas, USA) to examine the interactions between land use and physiography and their combined influences on riverine nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively). The response of nutrient concentrations to spatial patterns of land use and physiography depended on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients, whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients when studying the interactions between a river and its watershed, especially in large, complex watersheds or those that cross steep environmental gradients.
Freshwater mussels (Family Unionidae) are among the most imperiled group of organisms in the worl... more Freshwater mussels (Family Unionidae) are among the most imperiled group of organisms in the world, with nearly 65% of North American species considered endangered. Anthropogenic disturbances, including altered flow regimes, habitat alteration, and pollution, are the major driver of this group's decline. We investigated the effects of tertiary treated municipal wastewater effluent on survivorship, growth, and condition of freshwater mussels in experimental cages in a small Central Texas stream. We tested the effluent effects by measuring basic physical parameters of native three ridge mussels (Amblema plicata) and of nonnative Asian clams (Corbicula fluminea), before and after 72-day exposure at four sites above and below a municipal wastewater treatment plant outfall. Survivorship and growth of the non-native Asian clams and growth and condition indices of the native three ridge mussels were significantly higher at the reference site above the outfall than in downstream sites. We attribute this reduction in fitness below the outfall to elevated nutrient and heavy metal concentrations, and the potential presence of other untested-for compounds commonly found in municipal effluent. These results, along with an absence of native mussels below the discharge, indicate a significant negative impact of wastewater effluent on both native and non-native mussels in the stream.
The effect of red-eared sliders (Trachemys scripta elegans) on aquatic ecosystem processes and ma... more The effect of red-eared sliders (Trachemys scripta elegans) on aquatic ecosystem processes and macroinvertebrate community was investigated in artificial ponds that were stocked with turtles or kept free of them. Compared to ponds without turtles, ponds with turtles displayed significantly higher values of pH, conductivity, sediment accumulation, and leaf litter decomposition rates, as well as a higher abundance of invertebrates, specifically that of the Hemiptera and Ephemeroptera. The biomass of periphyton was not affected by the presence of turtles. These results suggest that the presence of T. s. elegans affects environmental conditions in ponds, and thus potentially ecosystem processes. Reduced abundance or loss of turtles in aquatic systems could therefore result in significant consequences on ecosystem functioning.
Terrestrial food subsidies are important energy sources to stream fishes worldwide. However, thei... more Terrestrial food subsidies are important energy sources to stream fishes worldwide. However, their importance is not fully understood, except perhaps for some salmonid communities. Using the published literature, we investigated patterns of fish taxonomy and jaw morphology in the consumption of terrestrial food subsidies by nonsalmonid stream fishes in the USA. We hypothesised that: (1) in general, non-salmonid fishes would consume terrestrial food items to the same extent as salmonids; and (2) subsidy consumption would be associated with jaw morphology. Cyprinids and fundulids consumed terrestrial subsidies approaching levels observed in salmonids (20-44%) whereas other groups (e.g. catostomids and moronids) consumed far less (,2%) terrestrial food. Fishes with terminal jaw positions tended to consume more terrestrial items than those with subterminal or inferior jaw positions. Within a species, there were highly variable propensities for consuming terrestrial subsidies. Our findings justify focusing on trophic linkages between fishes and riparian systems across a wide range of taxa, especially considering the spatio-temporal variability of environmental conditions across a variety of habitats. It is necessary to assess the relative contribution of terrestrial subsidies in fish growth and population dynamics with a focus on nutritional and energetic benefits across different groups.
Ecological subsidies are materials and energy that cross a boundary between two ecosystems. An ex... more Ecological subsidies are materials and energy that cross a boundary between two ecosystems. An example is terrestrial leaf litter that falls into a stream to ultimately become the basis of the stream food web. Terrestrial arthropods that fall into streams are often an important food resource for fishes, but variation in the nutritional quality of aquatic versus terrestrial items has not been fully assessed. Carbon and nitrogen ratios in invertebrates roughly reflect relative amounts of structural chitin and since chitin is mostly indigestible to fishes, it can be an indicator of food quality, where a greater amount of chitin (or greater C:N) indicates lower quality. To better understand potential differences in the quality of terrestrial versus aquatic arthropods, we sampled terrestrial and aquatic arthropods during winter, spring, and summer, and measured their molar C:N values. We tested arthropod C:N values for origin (terrestrial vs. aquatic), taxonomy (order level), and time of year (winter, spring, and summer). We did not detect significant differences in any of these comparisons. The average molar C:N (AE 1 SD) for aquatic arthropods (n ¼ 81 samples) was 5.0 AE 0.6 and ranged from 4.7 to 5.6 and that for terrestrial arthropods (n ¼ 42 samples) was 5.1 AE 0.7 and ranged from 4.4 to 5.6. Molar C:N values were not different among aquatic and terrestrial arthropods (df ¼ 74.3, t ¼ À0.995, p ¼ 0.418) and did not differ across arthropod taxa (F 7,50 ¼ 1.9, p ¼ 0.087). Any trends in molar C:N variability in arthropods, whether they be aquatic or terrestrial, are probably due to relative amounts of structural chitin. Since chitin is largely undigested in fish diets, molar C:N might be important in considering the true benefits of terrestrial subsidies on fish life histories.
G. M. 2011: Mountain ridge and sea: Geographic-barrier effects on genetic diversity and different... more G. M. 2011: Mountain ridge and sea: Geographic-barrier effects on genetic diversity and differentiation of the Hong Kong newt (Paramesotriton hongkongensis) revealed by AFLP. -Ann. Zool. Fennici 48: 119-127.
Cross-ecosystem subsidies, such as terrestrial invertebrates and leaf litter falling into water a... more Cross-ecosystem subsidies, such as terrestrial invertebrates and leaf litter falling into water as resources for aquatic communities, can vary across environmental gradients. We examined whether the effect of terrestrial subsidy inputs on benthic invertebrates was mediated by resident coastal cutthroat trout (Oncorhynchus clarki) in two representative streams. We experimentally manipulated the input rates (reduced, ambient) of terrestrial subsidies (terrestrial invertebrates and leaf litter) as well as the presence or absence of cutthroat trout in the two streams. The hypothesis that the reduction of terrestrial subsidies to the stream influences benthic invertebrate assemblages was supported by experimental results. The treatments of terrestrial subsidy reduction and cutthroat trout presence had a significant negative effect on benthic invertebrate community biomass and shredder biomass in East Creek with high natural terrestrial subsidy input and small amount of large wood in channel. In contrast, results from Spring Creek with low subsidy input and large amount of large wood in channel showed that only the terrestrial subsidy reduction significantly reduced the biomass of shredders. The effects of the terrestrial subsidy input and trout predation on benthic invertebrate communities varied between the two streams.
Your article is protected by copyright and all rights are held exclusively by Springer Basel AG. ... more Your article is protected by copyright and all rights are held exclusively by Springer Basel AG. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
Terrestrial arthropods might represent an important energy source for stream predators, but these... more Terrestrial arthropods might represent an important energy source for stream predators, but these trophic linkages have seldom been studied in the tropics. Terrestrial arthropod inputs (essentially, arthropod 'rain') into four streams with different riparian vegetation (two draining shrublands and two draining forests) were measured over three consecutive seasons (dry, wet, dry) from 2005 to 2007 in monsoonal Hong Kong. Predatory minnows, Parazacco spilurus (Cyprinidae), were collected and their consumption of terrestrial arthropods was estimated. Inputs of arthropods were dominated by Diptera, Collembola, Formicidae and aerial Hymenoptera, accounting for ≥73% of the arthropod abundance. Seasonal variation was marked: numbers in the dry seasons were approximately half (47-57%) those in the wet season, and biomass fell to one-third (33-37%) of the wet-season value. Shrubland streams received 19-43% fewer individuals and 6-34% less biomass than shaded forest streams. An analysis of fish diets in three of the four streams showed that terrestrial insects and spiders were more important prey in the two forest streams, accounting for 35-43% of prey abundance (39-43% by volume) v. 28% (27%) in the shrubland stream. Because riparian vegetation is the source of terrestrial arthropod inputs to streams, degradation of streamside forests that reduce these inputs will have consequences for the diets of stream fishes.
Spiders that are abundant along streams may depend on energy subsidies across land–water ecotones... more Spiders that are abundant along streams may depend on energy subsidies across land–water ecotones, but the effects of season and habitat structure on this trophic linkage remain poorly understood in the tropics. We carried out surveys and a manipulative experiment to investigate the effects of season and substrate availability on the distribution of riparian orb-web spiders in Hong Kong, southern China. In the surveys, spider abundance, prey, substrate use, and web orientation were recorded. The experiment involved installation of in-stream artificial substrates (ropes and bamboo poles) to increase substrate availability for web attachment. We found no seasonal difference in web abundance, but seasonal differences were observed for the prey on webs: aquatic insects (mostly Ephemeroptera and chironomid midges) contributed 69 percent of total prey collected during the wet season, but only 38 percent during the dry season. Most webs (50–80%) were < 0.5 m above the water and 45–51 percent of them tended to be orientated horizontally to the water surface and supported by overhanging vegetation and boulders. The addition of artificial substrates resulted in a 23–34 percent increase in the number of webs at the four treatment sites compared to controls, indicating that availability of web-building substrates is a critical determinant of the spider distribution. Our results suggest that riparian zones are potential ‘hotspots' of food availability for spiders, and that the aquatic insect subsidy allows this habitat to support increased densities of spiders when the constraint of substrate availability is relaxed.
Spatial subsidies of energy and nutrients can influence the distribution of consumers in riparian... more Spatial subsidies of energy and nutrients can influence the distribution of consumers in riparian habitats. This study compared the abundance and composition of bird assemblages and the availability of volant insect prey within the riparian zone (≤ 30 m from the stream) and further inland (100-250 m away) within a secondary forest in monsoonal Hong Kong. Replicated point-counts of birds and insect light trapping were conducted in each zone during the wet and dry season of 2006-2007. The biomass of adult aquatic insects in the riparian zone was nine to 12 times higher than inland during both seasons, however, total insect biomass (aquatic plus terrestrial insects) in the riparian zone was only 49 percent (wet season) and 18 percent (dry season) greater. More birds (both numbers of individuals and species) were recorded in the riparian zone, and this difference was particularly conspicuous during the wet season. Most of the wet-season difference was due to the greater number of insectivorous birds in the riparian zone (123% greater than inland), and may have reflected the relative availability of adult aquatic insects. These findings confirm the importance of riparian zones as feeding habitats for forest birds, and have implications for conservation planning and setting the boundaries of protected areas.
Organisms through phenotypic plasticity can cope with multiple changed environmental conditions. ... more Organisms through phenotypic plasticity can cope with multiple changed environmental conditions. Theory predicts that animals in streams and rivers should be able to balance demands of the needs to obtain food efficiently and to adjust response to hydrodynamic variability. This study examined effects of variations in food availability and current velocity on the feeding structure and growth rate of Simulium noelleri blackfly larvae. The larvae developed larger labral fans and more rays under slow current and low food regimes than in fast current and high food conditions. In both fast and slow current regimes, growth rates were higher and development periods to the final-instar stage were shorter in high food treatments. The estimated flux rates of food particles through labral fans under high food treatments for both fast and slow current regimes were higher than those under low food treatments. Although both food and current velocity appeared to have selected for flexibility of feeding structure and growth rate, food availability was a more important factor for phenotypic and developmental plasticity than current velocity. The results indicate a strong link between environmental changes in food availability and current velocity, phenotypic plasticity, and growth rate of S. noelleri. This study suggests that plasticity of ecomorphs with macroevolutionary significance may play a role in the early evolutionary stages of blackfly larvae.
The contribution of adult aquatic insects to riparian prey availability at four sites along three... more The contribution of adult aquatic insects to riparian prey availability at four sites along three hillstreams in Hong Kong was estimated during 2004-2006 dry and wet seasons using light traps deployed at different distances from the banks. The number and biomass of aquatic and terrestrial insects collected were markedly higher during the wet season. Numerically, aquatic insects (especially Chironomidae and Philopotamidae) remained a major catch component along banks throughout the year comprising 77% (range: 61-85%) of total insects. Their contribution to total biomass was higher in the wet season (mean: 50%, range: 33-62%) than during the dry season (mean: 21%, range: 8-45%). Aquatic insect abundance decreased with increasing distance from streams during both seasons: numbers at 10-20 m distance were less than 45% of those at the banks, declining to less than 13% at 80 m distance. No such decline with distance was observed for terrestrial insects, but the limited dispersal of aquatic insects meant total insect catches were highest along stream banks. Changes in biomass with distance from streams were similar to those for abundance. Adult aquatic insects may represent an important water-to-land energy subsidy for riparian predators in Hong Kong, but the magnitude varied seasonally and fell sharply with increasing distance from streams.
Abstract: Riverine ecosystems are linked to their watersheds, and both land use and physiographic... more Abstract: Riverine ecosystems are linked to their watersheds, and both land use and physiographic environmental
conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship
with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas,
USA) to examine the interactions between land use and physiography and their combined influences on riverine
nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients
explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively).
The response of nutrient concentrations to spatial patterns of land use and physiography depended
on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were
associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the
catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality
and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients,
whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on
dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients
when studying the interactions between a river and its watershed, especially in large, complex watersheds or those
that cross steep environmental gradients.
Background/Question/Methods In order to understand biodiversity-ecosystem functioning relationshi... more Background/Question/Methods In order to understand biodiversity-ecosystem functioning relationship, we examined effects of riparian vegetation diversity on leaf litter decomposition in a stream. Because terrestrial leaf-litter is the dominant energy source to many streams, riparian vegetation diversity can have profound influence on streams ecosystems, which are impacted by human watershed disturbances, including species losses and non-native species introduction. If introduced tree species influences biodiversity-ecosystem functioning relationship in streams is largely unknown. The objective of this study is to assess the effects of tree species diversity (five native riparian species and one introduced species) on leaf litter breakdown in a stream. We conducted a field experiment over 56 days in Barton Creek (Central Texas) to examine temporal patterns of litter breakdown and to detect any non-additive effects of litter diversity on decomposition. The 12 treatments of leaf-bags we...
Light pollution can reduce night time drift of larval aquatic insects in urban streams by disrupt... more Light pollution can reduce night time drift of larval aquatic insects in urban streams by disrupting their circadian rhythms. Previous studies on larval insect drift show that disruption in drift leads to changes in reproduction as well as intraspecific and interspecific interactions. The purpose of this study was to conduct a preliminary investigation into the effects of extreme artificial light on insect drift in urbanized, high clarity spring systems of the karst Edwards Plateau, TX. We quantified taxa richness, diversity, and abundance in aquatic insect night time drift under two treatments (ambient night time light and artificial light addition) and among five streams using a paired design. Richness and diversity of drifting aquatic insects were similar between treatments but abundance was 37% less in the light addition treatment than that of the control. Effects of light addition on mean abundance was more notable in large streams with a 58% decrease in Simuliidae (compared to that of the control) and 51% decrease in Baetidae. Reduced drift from light addition suggests the potential of artificial lighting disrupting insect drift and consequently community structure. Results of this experiment support a growing body of knowledge on how urbanized systems influence stream communities.
Riverine ecosystems are linked to their watersheds, and both land use and physiographic environme... more Riverine ecosystems are linked to their watersheds, and both land use and physiographic environmental conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas, USA) to examine the interactions between land use and physiography and their combined influences on riverine nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively). The response of nutrient concentrations to spatial patterns of land use and physiography depended on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients, whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients when studying the interactions between a river and its watershed, especially in large, complex watersheds or those that cross steep environmental gradients.
Freshwater mussels (Family Unionidae) are among the most imperiled group of organisms in the worl... more Freshwater mussels (Family Unionidae) are among the most imperiled group of organisms in the world, with nearly 65% of North American species considered endangered. Anthropogenic disturbances, including altered flow regimes, habitat alteration, and pollution, are the major driver of this group's decline. We investigated the effects of tertiary treated municipal wastewater effluent on survivorship, growth, and condition of freshwater mussels in experimental cages in a small Central Texas stream. We tested the effluent effects by measuring basic physical parameters of native three ridge mussels (Amblema plicata) and of nonnative Asian clams (Corbicula fluminea), before and after 72-day exposure at four sites above and below a municipal wastewater treatment plant outfall. Survivorship and growth of the non-native Asian clams and growth and condition indices of the native three ridge mussels were significantly higher at the reference site above the outfall than in downstream sites. We attribute this reduction in fitness below the outfall to elevated nutrient and heavy metal concentrations, and the potential presence of other untested-for compounds commonly found in municipal effluent. These results, along with an absence of native mussels below the discharge, indicate a significant negative impact of wastewater effluent on both native and non-native mussels in the stream.
The effect of red-eared sliders (Trachemys scripta elegans) on aquatic ecosystem processes and ma... more The effect of red-eared sliders (Trachemys scripta elegans) on aquatic ecosystem processes and macroinvertebrate community was investigated in artificial ponds that were stocked with turtles or kept free of them. Compared to ponds without turtles, ponds with turtles displayed significantly higher values of pH, conductivity, sediment accumulation, and leaf litter decomposition rates, as well as a higher abundance of invertebrates, specifically that of the Hemiptera and Ephemeroptera. The biomass of periphyton was not affected by the presence of turtles. These results suggest that the presence of T. s. elegans affects environmental conditions in ponds, and thus potentially ecosystem processes. Reduced abundance or loss of turtles in aquatic systems could therefore result in significant consequences on ecosystem functioning.
Terrestrial food subsidies are important energy sources to stream fishes worldwide. However, thei... more Terrestrial food subsidies are important energy sources to stream fishes worldwide. However, their importance is not fully understood, except perhaps for some salmonid communities. Using the published literature, we investigated patterns of fish taxonomy and jaw morphology in the consumption of terrestrial food subsidies by nonsalmonid stream fishes in the USA. We hypothesised that: (1) in general, non-salmonid fishes would consume terrestrial food items to the same extent as salmonids; and (2) subsidy consumption would be associated with jaw morphology. Cyprinids and fundulids consumed terrestrial subsidies approaching levels observed in salmonids (20-44%) whereas other groups (e.g. catostomids and moronids) consumed far less (,2%) terrestrial food. Fishes with terminal jaw positions tended to consume more terrestrial items than those with subterminal or inferior jaw positions. Within a species, there were highly variable propensities for consuming terrestrial subsidies. Our findings justify focusing on trophic linkages between fishes and riparian systems across a wide range of taxa, especially considering the spatio-temporal variability of environmental conditions across a variety of habitats. It is necessary to assess the relative contribution of terrestrial subsidies in fish growth and population dynamics with a focus on nutritional and energetic benefits across different groups.
Ecological subsidies are materials and energy that cross a boundary between two ecosystems. An ex... more Ecological subsidies are materials and energy that cross a boundary between two ecosystems. An example is terrestrial leaf litter that falls into a stream to ultimately become the basis of the stream food web. Terrestrial arthropods that fall into streams are often an important food resource for fishes, but variation in the nutritional quality of aquatic versus terrestrial items has not been fully assessed. Carbon and nitrogen ratios in invertebrates roughly reflect relative amounts of structural chitin and since chitin is mostly indigestible to fishes, it can be an indicator of food quality, where a greater amount of chitin (or greater C:N) indicates lower quality. To better understand potential differences in the quality of terrestrial versus aquatic arthropods, we sampled terrestrial and aquatic arthropods during winter, spring, and summer, and measured their molar C:N values. We tested arthropod C:N values for origin (terrestrial vs. aquatic), taxonomy (order level), and time of year (winter, spring, and summer). We did not detect significant differences in any of these comparisons. The average molar C:N (AE 1 SD) for aquatic arthropods (n ¼ 81 samples) was 5.0 AE 0.6 and ranged from 4.7 to 5.6 and that for terrestrial arthropods (n ¼ 42 samples) was 5.1 AE 0.7 and ranged from 4.4 to 5.6. Molar C:N values were not different among aquatic and terrestrial arthropods (df ¼ 74.3, t ¼ À0.995, p ¼ 0.418) and did not differ across arthropod taxa (F 7,50 ¼ 1.9, p ¼ 0.087). Any trends in molar C:N variability in arthropods, whether they be aquatic or terrestrial, are probably due to relative amounts of structural chitin. Since chitin is largely undigested in fish diets, molar C:N might be important in considering the true benefits of terrestrial subsidies on fish life histories.
G. M. 2011: Mountain ridge and sea: Geographic-barrier effects on genetic diversity and different... more G. M. 2011: Mountain ridge and sea: Geographic-barrier effects on genetic diversity and differentiation of the Hong Kong newt (Paramesotriton hongkongensis) revealed by AFLP. -Ann. Zool. Fennici 48: 119-127.
Cross-ecosystem subsidies, such as terrestrial invertebrates and leaf litter falling into water a... more Cross-ecosystem subsidies, such as terrestrial invertebrates and leaf litter falling into water as resources for aquatic communities, can vary across environmental gradients. We examined whether the effect of terrestrial subsidy inputs on benthic invertebrates was mediated by resident coastal cutthroat trout (Oncorhynchus clarki) in two representative streams. We experimentally manipulated the input rates (reduced, ambient) of terrestrial subsidies (terrestrial invertebrates and leaf litter) as well as the presence or absence of cutthroat trout in the two streams. The hypothesis that the reduction of terrestrial subsidies to the stream influences benthic invertebrate assemblages was supported by experimental results. The treatments of terrestrial subsidy reduction and cutthroat trout presence had a significant negative effect on benthic invertebrate community biomass and shredder biomass in East Creek with high natural terrestrial subsidy input and small amount of large wood in channel. In contrast, results from Spring Creek with low subsidy input and large amount of large wood in channel showed that only the terrestrial subsidy reduction significantly reduced the biomass of shredders. The effects of the terrestrial subsidy input and trout predation on benthic invertebrate communities varied between the two streams.
Your article is protected by copyright and all rights are held exclusively by Springer Basel AG. ... more Your article is protected by copyright and all rights are held exclusively by Springer Basel AG. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
Terrestrial arthropods might represent an important energy source for stream predators, but these... more Terrestrial arthropods might represent an important energy source for stream predators, but these trophic linkages have seldom been studied in the tropics. Terrestrial arthropod inputs (essentially, arthropod 'rain') into four streams with different riparian vegetation (two draining shrublands and two draining forests) were measured over three consecutive seasons (dry, wet, dry) from 2005 to 2007 in monsoonal Hong Kong. Predatory minnows, Parazacco spilurus (Cyprinidae), were collected and their consumption of terrestrial arthropods was estimated. Inputs of arthropods were dominated by Diptera, Collembola, Formicidae and aerial Hymenoptera, accounting for ≥73% of the arthropod abundance. Seasonal variation was marked: numbers in the dry seasons were approximately half (47-57%) those in the wet season, and biomass fell to one-third (33-37%) of the wet-season value. Shrubland streams received 19-43% fewer individuals and 6-34% less biomass than shaded forest streams. An analysis of fish diets in three of the four streams showed that terrestrial insects and spiders were more important prey in the two forest streams, accounting for 35-43% of prey abundance (39-43% by volume) v. 28% (27%) in the shrubland stream. Because riparian vegetation is the source of terrestrial arthropod inputs to streams, degradation of streamside forests that reduce these inputs will have consequences for the diets of stream fishes.
Spiders that are abundant along streams may depend on energy subsidies across land–water ecotones... more Spiders that are abundant along streams may depend on energy subsidies across land–water ecotones, but the effects of season and habitat structure on this trophic linkage remain poorly understood in the tropics. We carried out surveys and a manipulative experiment to investigate the effects of season and substrate availability on the distribution of riparian orb-web spiders in Hong Kong, southern China. In the surveys, spider abundance, prey, substrate use, and web orientation were recorded. The experiment involved installation of in-stream artificial substrates (ropes and bamboo poles) to increase substrate availability for web attachment. We found no seasonal difference in web abundance, but seasonal differences were observed for the prey on webs: aquatic insects (mostly Ephemeroptera and chironomid midges) contributed 69 percent of total prey collected during the wet season, but only 38 percent during the dry season. Most webs (50–80%) were < 0.5 m above the water and 45–51 percent of them tended to be orientated horizontally to the water surface and supported by overhanging vegetation and boulders. The addition of artificial substrates resulted in a 23–34 percent increase in the number of webs at the four treatment sites compared to controls, indicating that availability of web-building substrates is a critical determinant of the spider distribution. Our results suggest that riparian zones are potential ‘hotspots' of food availability for spiders, and that the aquatic insect subsidy allows this habitat to support increased densities of spiders when the constraint of substrate availability is relaxed.
Spatial subsidies of energy and nutrients can influence the distribution of consumers in riparian... more Spatial subsidies of energy and nutrients can influence the distribution of consumers in riparian habitats. This study compared the abundance and composition of bird assemblages and the availability of volant insect prey within the riparian zone (≤ 30 m from the stream) and further inland (100-250 m away) within a secondary forest in monsoonal Hong Kong. Replicated point-counts of birds and insect light trapping were conducted in each zone during the wet and dry season of 2006-2007. The biomass of adult aquatic insects in the riparian zone was nine to 12 times higher than inland during both seasons, however, total insect biomass (aquatic plus terrestrial insects) in the riparian zone was only 49 percent (wet season) and 18 percent (dry season) greater. More birds (both numbers of individuals and species) were recorded in the riparian zone, and this difference was particularly conspicuous during the wet season. Most of the wet-season difference was due to the greater number of insectivorous birds in the riparian zone (123% greater than inland), and may have reflected the relative availability of adult aquatic insects. These findings confirm the importance of riparian zones as feeding habitats for forest birds, and have implications for conservation planning and setting the boundaries of protected areas.
Organisms through phenotypic plasticity can cope with multiple changed environmental conditions. ... more Organisms through phenotypic plasticity can cope with multiple changed environmental conditions. Theory predicts that animals in streams and rivers should be able to balance demands of the needs to obtain food efficiently and to adjust response to hydrodynamic variability. This study examined effects of variations in food availability and current velocity on the feeding structure and growth rate of Simulium noelleri blackfly larvae. The larvae developed larger labral fans and more rays under slow current and low food regimes than in fast current and high food conditions. In both fast and slow current regimes, growth rates were higher and development periods to the final-instar stage were shorter in high food treatments. The estimated flux rates of food particles through labral fans under high food treatments for both fast and slow current regimes were higher than those under low food treatments. Although both food and current velocity appeared to have selected for flexibility of feeding structure and growth rate, food availability was a more important factor for phenotypic and developmental plasticity than current velocity. The results indicate a strong link between environmental changes in food availability and current velocity, phenotypic plasticity, and growth rate of S. noelleri. This study suggests that plasticity of ecomorphs with macroevolutionary significance may play a role in the early evolutionary stages of blackfly larvae.
The contribution of adult aquatic insects to riparian prey availability at four sites along three... more The contribution of adult aquatic insects to riparian prey availability at four sites along three hillstreams in Hong Kong was estimated during 2004-2006 dry and wet seasons using light traps deployed at different distances from the banks. The number and biomass of aquatic and terrestrial insects collected were markedly higher during the wet season. Numerically, aquatic insects (especially Chironomidae and Philopotamidae) remained a major catch component along banks throughout the year comprising 77% (range: 61-85%) of total insects. Their contribution to total biomass was higher in the wet season (mean: 50%, range: 33-62%) than during the dry season (mean: 21%, range: 8-45%). Aquatic insect abundance decreased with increasing distance from streams during both seasons: numbers at 10-20 m distance were less than 45% of those at the banks, declining to less than 13% at 80 m distance. No such decline with distance was observed for terrestrial insects, but the limited dispersal of aquatic insects meant total insect catches were highest along stream banks. Changes in biomass with distance from streams were similar to those for abundance. Adult aquatic insects may represent an important water-to-land energy subsidy for riparian predators in Hong Kong, but the magnitude varied seasonally and fell sharply with increasing distance from streams.
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Papers by Yixin Zhang
conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship
with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas,
USA) to examine the interactions between land use and physiography and their combined influences on riverine
nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients
explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively).
The response of nutrient concentrations to spatial patterns of land use and physiography depended
on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were
associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the
catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality
and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients,
whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on
dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients
when studying the interactions between a river and its watershed, especially in large, complex watersheds or those
that cross steep environmental gradients.
richness, diversity, and abundance in aquatic insect night time drift under two treatments (ambient night time light and artificial light addition) and among five streams using a paired design. Richness and diversity of drifting aquatic insects were
similar between treatments but abundance was 37% less in the light addition treatment than that of the control. Effects of light addition on mean abundance was more notable in large streams with a 58% decrease in Simuliidae (compared to that of the control) and 51% decrease in Baetidae. Reduced drift from light addition suggests the potential of artificial lighting disrupting insect drift and consequently community structure. Results of this experiment support a growing body of knowledge on how urbanized systems influence stream communities.
on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were
associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients, whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients when studying the interactions between a river and its watershed, especially in large, complex watersheds or those that cross steep environmental gradients.
below the discharge, indicate a significant negative impact of wastewater effluent on both native and non-native mussels in the stream.
conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship
with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas,
USA) to examine the interactions between land use and physiography and their combined influences on riverine
nutrient dynamics. Patterns in physiography and land use were highly correlated, but physiographic gradients
explained ∼2× more of the variability in riverine nutrient concentrations than land use (25 and 12%, respectively).
The response of nutrient concentrations to spatial patterns of land use and physiography depended
on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were
associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the
catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality
and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients,
whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on
dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients
when studying the interactions between a river and its watershed, especially in large, complex watersheds or those
that cross steep environmental gradients.
richness, diversity, and abundance in aquatic insect night time drift under two treatments (ambient night time light and artificial light addition) and among five streams using a paired design. Richness and diversity of drifting aquatic insects were
similar between treatments but abundance was 37% less in the light addition treatment than that of the control. Effects of light addition on mean abundance was more notable in large streams with a 58% decrease in Simuliidae (compared to that of the control) and 51% decrease in Baetidae. Reduced drift from light addition suggests the potential of artificial lighting disrupting insect drift and consequently community structure. Results of this experiment support a growing body of knowledge on how urbanized systems influence stream communities.
on the specific nutrient and scale of analysis. However, elevated dissolved nutrient concentrations typically were
associated with areas of higher rainfall, greater stream density, and more intensive human alteration of the catchment. In contrast, particulate nutrients were more responsive to catchment area and seasonality. Seasonality and reach-scale % rangeland had the strongest independent effects on concentrations of particulate nutrients, whereas the specific ecoregion type and catchment-scale % urban use had the strongest independent effects on dissolved nutrients. Our study highlights the importance of incorporating physiographic environmental gradients when studying the interactions between a river and its watershed, especially in large, complex watersheds or those that cross steep environmental gradients.
below the discharge, indicate a significant negative impact of wastewater effluent on both native and non-native mussels in the stream.