Person:

Jiang, Lin

Permanent Link

https://hdl.handle.net/1853/71372

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Organizational Unit

School of Biological Sciences

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Now showing 1 - 10 of 10

Essays on cooperation and/or competition within R&D communities

(Georgia Institute of Technology, 2010-07-01) Jiang, Lin

This dissertation attempts to contribute to our understanding of how firms can manage and benefit from its research and development (R&D) communities. In the first essay, we examine how established firms can leverage a broad R&D community to invent successfully during the early stage of a technological change. We find significant inventions by incumbents outside the existing dominant designs and relate their success to their willingness to search novel areas, explore scientific knowledge in the public domain, and form alliances with a balanced portfolio of partners. We find support for the hypotheses using data from the global semiconductor industry between 1989 and 2002. In the second essay, we examine a classical choice within an R&D community: cooperation or competition with other firms along a technology supply chain. We find that the answer depends not just on the transaction costs, strength of intellectual property protection rights, and asset cospecialization in the buyers' industries, but also the supplier's knowledge transfer capability and a typical buyer's productivity in developing licensed inventions. For instance, the effect of asset cospecialization on licensing is moderated by the factors that affect the buyers' productivity in developing external technology. Additionally, factors that reduce the buyers' development productivity can be mitigated by the supplier's knowledge transfer capability. We find empirical supports for these predictions using a cross-industry panel dataset of a sample of 345 U.S. small technology-based firms for the 1996-2007 period. In the third essay, I develop two game theoretical models to address how research competition from academic researchers affects firms' openness in disclosing intermediate R&D outcomes. Both models predict that such competition increases the firm's incentive to publish research findings, even though the firm would not have had such an incentive without the presence of the competition. The models also suggest several conditions under which the effect takes place. I further discuss the implications of ownership fragmentation for research materials within the scientific community and academic researchers' engagement in entrepreneurial activities. As implied by my models, these phenomena might instigate withholding of research findings by firms.
An experimental test of Darwin's naturalization hypothesis

(Georgia Institute of Technology, 2010-02-19) Jiang, Lin ; Tan, Jiaqi ; Pu, Zhichao

One of the oldest ideas in invasion biology, known as Darwin’s naturalization hypothesis, suggests that introduced species are more successful in communities in which their close relatives are absent. We conducted the first experimental test of this hypothesis in laboratory bacterial communities varying in phylogenetic relatedness between resident and invading species with and without a protist bacterivore. As predicted, invasion success increased with phylogenetic distance between the invading and the resident bacterial species in both the presence and the absence of protistan bacterivory. The frequency of successful invader establishment was best explained by average phylogenetic distance between the invader and all resident species, possibly indicating limitation by the availability of the unexploited niche (i.e., organic substances in the medium capable of supporting the invader growth); invader abundance was best explained by phylogenetic distance between the invader and its nearest resident relative, possibly indicating limitation by the availability of the unexploited optimal niche (i.e., the subset of organic substances supporting the best invader growth). These results were largely driven by one resident bacterium (a subspecies of Serratia marcescens) posting the strongest resistance to the alien bacterium (another subspecies of S. marcescens). Overall, our findings support phylogenetic relatedness as a useful predictor of species invasion success.
Competition for biotic resources and coexistence in variable environments

(Georgia Institute of Technology, 2009-12-01) Jiang, Lin
Different Effects of Species Diversity on Temporal Stability in Single‐Trophic and Multitrophic Communities

(Georgia Institute of Technology, 2009-11) Jiang, Lin ; Pu, Zhichao

The question of how species diversity affects ecological stability has long interested ecologists and yet remains largely unresolved. Historically, attempts to answer this question have been hampered by the presence of multiple potentially confounding stability concepts, confusion over responses at different levels of ecological organization, discrepancy between theoretical predictions, and, particularly, the paucity of empirical studies. Here we used meta‐analyses to synthesize results of empirical studies published primarily in the past 2 decades on the relationship between species diversity and temporal stability. We show that the overall effect of increasing diversity was positive for community‐level temporal stability but neutral for population‐level temporal stability. There were, however, striking differences in the diversity‐stability relationship between single‐ and multitrophic systems, with diversity stabilizing both population and community dynamics in multitrophic but not single‐trophic communities. These patterns were broadly equivalent across experimental and observational studies as well as across terrestrial and aquatic studies. We discuss possible mechanisms for population stability to increase with diversity in multitrophic systems and for diversity to influence community‐level stability in general. Overall, our results indicate that diversity can affect temporal stability, but the effects may critically depend on trophic complexity.
Predation Alters Relationships between biodiversity and Temporal Stability

(Georgia Institute of Technology, 2009-03) Jiang, Lin ; Joshi, Hena ; Patel, Shivani N.

Ecologists disagree on how diversity affects stability. At the heart of the controversy is the relationship between diversity and population stability, with conflicting findings from both theoretical and empirical studies. To help reconcile these results, we propose that this relationship may depend on trophic complexity, such that positive relations tend to emerge in multitrophic but not singletrophic communities. This hypothesis is based on the premise that stabilizing weak trophic interactions restrain population oscillations associated with strong trophic interactions in diverse multitrophic communities. We tested this hypothesis using simple freshwater bacterivorous protist communities differing in diversity with and without a predatory protist species. Coupling weak and strong trophic interactions reduced population temporal variability of the stronginteracting species, supporting the stabilizing role of weak interactions. In keeping with our hypothesis, predation altered the overall effect of diversity on population temporal stability and, in particular, caused a reversal of the diversity-stability relationship (negative without predators and positive with predators) for the strong-interacting species. A similar role of predation was also observed when examining the relationship between diversity and temporal stability of community biomass. Together, these findings demonstrated strong interactive effects of trophic interactions and diversity on temporal stability of population and community properties.
Community assembly in the presence of disturbance: a microcosm experiment

(Georgia Institute of Technology, 2008-05) Jiang, Lin ; Patel, Shivani N.

Ecologists know relatively little about the manner in which disturbance affects the likelihood of alternative community stable states and how the history of community assembly affects the relationship between disturbance and species diversity. Using microbial communities comprising bacterivorous ciliated protists assembled in laboratory microcosms, we experimentally investigated these questions by independently manipulating the intensity of disturbance (in the form of density-independent mortality) and community assembly history (including a control treatment with simultaneous species introduction and five sequential assembly treatments). Species diversity patterns consistent with the intermediate disturbance hypothesis emerged in the controls, as several species showed responses indicative of a trade-off between competitive ability and ability to recover from disturbance. Species diversity in communities with sequential assembly, however, generally declined with disturbance, owing to the increased extinction risk of later colonizers at the intermediate level of disturbance. Similarities among communities subjected to different assembly histories increased with disturbance, a result due possibly to increasing disturbance reducing the importance of competition and hence priority effects. This finding is most consistent with the idea that increasing disturbance tends to reduce the likelihood of alternative stable states. Collectively, these results indicate the strong interactive effects of disturbance and assembly history on the structure of ecological communities.
Negative selection effects suppress relationships between bacterial diversity and ecosystem functioning

(Georgia Institute of Technology, 2007-05) Jiang, Lin

I assembled bacterial communities to explore the effects of bacterial diversity on multiple ecosystem functions, including bacterial community biovolume, decomposition of particulate organic matter, and biomass transfer to the next trophic level. The experiment used a two-way factorial design with four levels of bacterial diversity (one to four species) and the absence/presence of a bacterivorous ciliated protist Tetrahymena pyriformis as two main factors, and all possible combinations of the four bacterial taxa nested within each diversity level. Bacterial community biovolume increased as bacterial diversity increased, a result due largely to positive selection effects. Decomposition and consumer abundance, however, were unaffected by bacterial diversity, though both varied among bacterial composition treatments. Negative selection effects, the dominance of species that do not contribute significantly to ecosystem functioning, accounted for the lack of diversity effects on decomposition and consumer abundance. The presence of Tetrahymena reduced bacterial community biovolume but increased decomposition, without altering the diversity–functioning relationships. Decomposition was strongly linked with consumer abundance such that communities supporting larger consumer biomass exhibited higher decomposition rates. This study suggests that if the negative selection effect is common, as it might be when examining ecosystem variables other than biomass (due to the presence of keystone species that can contribute disproportionably to ecosystem functioning relative to their abundances), basic bacteria-mediated ecosystem processes, such as decomposition and energy transfer to the next trophic level, may not increase with bacterial diversity.
Adaptive Evolution of Phytoplankton Cell Size

(Georgia Institute of Technology, 2005-10) Jiang, Lin ; Schofield, Oscar M. E. ; Falkowski, Paul G.

We present a simple nutrient‐phytoplankton‐zooplankton (NPZ) model that incorporates adaptive evolution and allometric relations to examine the patterns and consequences of adaptive changes in plankton body size. Assuming stable environmental conditions, the model makes the following predictions. First, phytoplankton should evolve toward small sizes typical of picoplankton. Second, in the absence of grazers, nutrient concentration is minimized as phytoplankton reach their fitness maximum. Third, increasing nutrient flux tends to increase phytoplankton cell size in the presence of phytoplankton‐zooplankton coevolution but has no effect in the absence of zooplankton. Fourth, phytoplankton reach their fitness maximum in the absence of grazers, and the evolutionary nutrient‐phytoplankton system has a stable equilibrium. In contrast, phytoplankton may approach their fitness minimum in the evolutionary NPZ system where phytoplankton and zooplankton are allowed to coevolve, which may result in oscillatory (unstable) dynamics of the evolutionary NPZ system, compared with the otherwise stable nonevolutionary NPZ system. These results suggest that evolutionary interactions between phytoplankton and zooplankton may have contributed to observed changes in phytoplankton sizes and associated biogeochemical cycles over geological time scales.
Predator Diet Breadth Influences the Relative Importance of Bottom-Up and Top-Down Control of Prey Biomass and Diversity

(Georgia Institute of Technology, 2005-03) Jiang, Lin ; Morin, Peter J.

We investigated the effects of predator diet breadth on the relative importance of bottom-up and top-down control of prey assemblages, using microbial food webs containing bacteria, bacterivorous protists and rotifers, and two different top predators. The experiment used a factorial design that independently manipulated productivity and the presence or absence of two top predators with different diet breadths. Predators included a "specialist" predatory ciliate Euplotes aediculatus, which was restricted to feeding on small prey, and a "generalist" predatory ciliate Stentor coeruleus, which could feed on the entire range of prey sizes. Both total prey biomass and prey diversity increased with productivity in the predator-free control and specialist predator treatments, a pattern consistent with bottom-up control, but both remained unchanged by productivity in the generalist predator treatment, a pattern consistent with top-down control. Linear food chain models adequately described responses in the generalist predator treatment, whereas food web models incorporating edible and inedible prey (which can coexist in the absence of predators) adequately described responses in the specialist predator treatment. These results suggest that predator diet breadth can play an important role in modulating the relative strength of bottom-up and top-down forces in ecological communities.
Autocorrelated exogenous factors and the detection of delayed density dependence

(Georgia Institute of Technology, 2003-08) Jiang, Lin ; Shao, Nan

Coupled trophic interactions with specialist predators or resources are thought to be primarily responsible for generating delayed density dependence. Previous theoretical studies suggest that autocorrelation in exogenous factors could generate apparent negative delayed density dependence in populations regulated only by direct density dependence. Using both linear and nonlinear models, we show that autocorrelated exogenous factors can generate the spurious appearance of not only negative, but also positive, delayed density dependence in populations regulated only by direct density dependence. Evidence for negative delayed density dependence is found mainly in populations exhibiting monotonic deterministic stability, whereas evidence for positive delayed density dependence is found mainly in populations exhibiting damped or persistent two-point cycles, or more complex deterministic dynamics. We argue that fluctuating resources (e.g., mast seeding) in bottom-up controlled communities could qualify as autocorrelated exogenous factors and cause apparent delayed density dependence in the population of their consumers.