Department of Biology
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Assistant Professor Phone: 512-245-3552 Fax: 512-245-8713 E-mail:yz11@txstate.edu Office: FAB 274 Department of Biology |
Research Interest |
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| My research interests focus on understanding ecological processes underlying stream ecosystems at a range of spatial scales. My small-scale researches involve functional morphology, phenotypic plasticity, emergent impacts of multiple predators on prey, and trout foraging-mode shift to study how habitat condition change influences these community properties. For large-scale research, I am working on the ecology of headwater stream systems, where I try to understand the effects of trophic flows across terrestrial-aquatic habitats on cutthroat trout growth and benthic community assemblages, watershed impacts of land use on stream physical structure and ecosystem functioning, and relationship between life-history attributes, landscape genetics and conservation. |
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| Functional morphology, phenotypic plasticity and community structure of black fly larvae Species assemblages in different habitats depend on ecosystem properties, in terms of physical setting and ecological processes, which influence organisms functional roles in the system. My previous works in stream ecology from laboratory experiments to regional surveys used black fly larvae as a model system to study how physical setting and ecological processes affect functional morphology, phenotypic plasticity, distribution, and community structure in a variety of lotic ecosystems with different habitat characteristics. The relationship among the morph-metrics of labral fans (modified mouthparts), body size and habitat characteristics was investigated for insights into the ecological processes of forming the adaptive morphological, hydrological, and phylogenetic traits of black fly larvae. A number of hypotheses on the distribution pattern of black fly larvae including fan traits-habitat relationships were tested in field studies (Zhang & Malmqvist 1996, Malmqvist, Zhang & Adler 1999). The patterns of fan phenotypic plasticity of two species in response to current velocity and food concentration were examined in laboratory experiments (Zhang & Malmqvist 1997, Zhang 2006). In a field experiment, I investigated the effects of fan morphological traits on feeding performance of several black fly species (Zhang 2000). In a large-scale field study, through an intensive field survey combining with a modeling approach (partial least squares projection to latent structures), we examined impacts of hydraulic disturbance of river regulation, biotic interactions, and food resources on the black fly larval community structure (Zhang, Malmqvist & Englund 1998). |
| Emergent predator-prey interactions: risk reduction and risk enhancement Most of ecosystems are characterized by multiple predators and food resource fluctuation at spatial and temporal scales. My interest in the area of predator-prey interaction is to examine the emergent impacts of multiple predators on a shared prey. In many cases, the emergent effects of multiple predators often cannot be predicted simply by a sum of individual effects of single predator types. Predation reduction refers to the case where the combined effect of multiple predators is smaller than the sum of single predator effects, whereas predation enhancement is that larger than the sum of individual effects of predators. The energetic state difference of predators may influence the interaction between predators by changing their flexible behaviors. I have tested this state-dependent predation hypothesis using one mayfly prey species and two sympatric dragonfly predators that have different foraging modes (sit-and-wait, and actively searching). Results present that predator energetic state variation affected consequences of emergent predator-prey interaction, in terms of risk enhancement and risk reduction. |
| Fish foraging-mode shift and its effects on benthic populations Consumer’s adaptive behavioral switches in food utilization in response to resource limitation are ubiquitous in natural food webs. Food availability can strongly affect predator–prey dynamics. When change in habitat condition reduces the availability of one prey type, predators often search for other prey, perhaps in a different habitat. Interactions between behavioral and morphological traits of different prey, such as prey activity and body coloration, may influence foraging success of visual predators. We tested the hypothesis that foraging success of stream-dwelling cutthroat trout (Onchorhyncus clarki) on cryptically colored, less-active benthic prey (larval mayfly; Paraleptophebia sp.) can be enhanced by the presence of distinctly colored, active prey (larval stonefly shredder; Despaxia augusta). Cutthroat trout preyed on benthic insects when drifting invertebrates were unavailable. When stonefly larvae were present, the trout ate most of the stoneflies and also consumed a higher proportion of mayflies than under mayfly only treatment. The putative mechanism is that active stonefly larvae supplied visual cues to the predator that alerted trout to the mayfly larvae. Foraging success of visual predators on cryptic prey can be enhanced by distinctly colored, active benthic taxa through unidirectional facilitation to the predators. This study suggests that prey– predator facilitation can modify species interactions that may affect community dynamics (Zhang & Richardson 2007). |
| Detritus processing, ecosystem engineering, and benthic diversity The interference between the species from different functional groups may influence ecosystem functioning and biological diversity. Do the interactions between predacious cutthroat trout and an omnivorous crayfish modify the crayfishs trophic and engineering effects within a detrital-based, stream benthic community? My field trough experiment shows that, as ecosystem processors and engineers, the omnivorous crayfish through their trophic and engineering roles can enhance detritus decomposition, reduce the accumulation of particulate organic matter, and diminish the diversity in leaf packs. Predatory cutthroat trout did not affect those variables and did not interfere with the crayfish (Zhang, Richardson & Negishi 2004). |
| Trophic flows across habitats and their effects on ecosystem processes One important aspect of terrestrial-aquatic linkages in riparian forest zones is trophic flows across habitats. Inputs of terrestrial trophic flows, such as leaf litter and terrestrial invertebrates, bring both nutrient and energetic resources into streams. How do the terrestrial arthropod inputs influence the growth of fish populations in headwater streams in young- and old-growth riparian forests? My experimental evidence indicates that the terrestrial arthropod input in summer may be a seasonal subsidy for cutthroat trout, but not a determined food resource for supporting cutthroat population growth in headwater streams in both clear-cut deciduous forests and old-growth coniferous forests. Ecologists realize that energy and nutrient subsidies transported across ecosystem boundaries are often key drivers of consumer-resource dynamics. How do marine-derived nutrients (salmon carcasses) influence the detrital processing and benthic food web in oligotrophic headwater streams? We found that salmon carcasses indirectly reduced alder leaf decomposition through temporarily decoupling the detrital resource-consumer relation within the short term. Detrital consumers shifted their diet to high-nutritional carcasses and grew larger. The results suggest that following the marine-derived nutrients pulse, this relation could be recoupled as the large consumers may shift their diet back to their original detrital resource and increase detrital processing (Zhang et al. 2003). |
| Cumulative watershed effects of land use on stream ecosystems Ecological studies show that historical land-use activities have had a variety of lasting effects on aquatic ecosystems. Watershed effects of human activities and disturbances accumulate in various landscapes where operations and management have occurred for long periods, which may change physical habitats, such as sedimentation, large wood debris reduction, and stream channel erosion, and result in community extinction at a local scale. By comparing 11 watersheds with different forest practice histories, we investigated impacts of past forest practices associating with cumulative watershed effects on streams ecosystems in Chilliwack River basin area in British Columbia. We detected characteristic differences of stream habitats that were related to past forestry operation. Reference study sites in well-matured forests were separated from recently impacted sites in a diagram of two principal components. Stream reaches in matured forests had coarser substrates than did stream reaches in young-growth forests that were impacted by recent forest practices. Through PLS modeling ( Partial least squares projection to latent structures ) and field-survey data analyzing, we found that reference reaches with high benthic species richness and high relative abundance were characterized by small volume of large woody debris, less FPOM and CPOM accumulated on substrate. A significant impact of past forestry practices was found at the test sites with recent disturbance. Species richness and relative abundance of benthic invertebrates at recently disturbed sites were significantly lower than that the model expected. The overall biomass of invertebrate communities at recently disturbed sites was significantly lower than that at the reference sites. This study provides evidence for the importance of past forest management practices associating with cumulative watershed effects in influencing habitat alteration and determining present-day stream biodiversity. |
| Life-history attributes, landscape genetics and conservation Variations in population attributes, such as population growth, age structure and dispersal, are influenced by environmental fluctuation and heterogeneous habitats, which are usually of more immediate importance for small populations. Landscape genetics combines landscape ecology and population genetics to study how landscape environmental variables affect population genetic structure and diversity. Landscape features such as islands, rivers and streams, and biotic interactions can influence ecological traits, dispersal, and gene flow among populations. The spatial detection and location of genetic discontinuities between populations is a key step of landscape genetics. This project is studying the Hong Kong newt (Paramesotriton hongkongensis), the only salamander species in Hong Kong, which is categorized as globally Near Threatened on the IUCN Red List of endangered species. Since it is likely to be included within a threatened category in the near future, conservation and management action for this animal must be formulated. However, the population ecology, genetic diversity, and gene flow among populations of P. hongkongensis have not been studied despite their fundamental importance to conservation of this protected species. In this research project, we are investigating the linkages among landscape features, life-history attributes, and population genetics relating with conservation of the Hong Kong newt. |
Education |
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| Postdoc | Stream Ecology | 2000-2003 | University of British Columbia, Canada |
| Postdoc | Stream Ecology | 1999-2000 | University of California at Santa Barbara, USA |
| Ph.D. | Animal Ecology | 1998 | Umeå University, Umeå, Sweden |
| M.Sc. | Animal Ecology | 1992 | Umeå University, Umeå, Sweden |
| B.Sc. | Biology | 1983 | Nanjing Normal University, Nanjing, China |
Publications |
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Courses Taught |
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General Entomology - Syllabus
Freshwater Ecology
Stream Ecology
Students & Postdocs |
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| Frances Lash | 2008 - | M.S. student (chair) |
| Susanna Scott | 2007 - | M.S. candidature, Texas State University |
| Tina Gonzales | 2007 - | M.S. student (committee) |
| Kristen Epp | 2006 - | Ph.D. student (committee) |