Biology subjects

Hsieh, C.-h.

Publications and source records attributed to Hsieh, C.-h..

7 recordsLinked to original sources

bioRxiv2025

Tracking changes in stability of North Sea Atlantic cod in 40 years

Tracking changes in the stability of low-abundance populations is vital for conservation. While the stability of natural populations is often assessed based on linear dynamics, many exhibit state-dependent dynamics, such as the iconic Atlantic cod in the North Sea (Gadus morhua). This fish population experienced an abrupt decline in the year 2000 and has not shown a clear sign of recovery despite relaxed fishing pressure. To understand the mechanisms behind the recovery dynamics, we used a dynamical systems approach to reconstruct the state space of the population from yearly abundance data of age groups between 1982-2021. Specifically, we estimated yearly interaction matrices of age groups and derived yearly population stability, defined as the rate of recovery to or departure from the current state after a small perturbation to the matrix. We found that since the abrupt decline in abundance of North Sea cod in the year 2000, the population continued to fluctuate closer to the transition threshold; some age groups experienced weaker self-regulation; and age-1 group became more sensitive to perturbations than older groups. These results provide important information on North Sea cods resilience and capacity to buffer natural and anthropogenic impacts.

ecology↗

bioRxiv2023

Larval thermosensitivity shapes adult population dynamics in Anopheles mosquitoes

Mosquitoes are vectors of human life-threatening pathogens, posing a significant global health threat. While the influence of temperature on mosquito life-history traits has been extensively studied in laboratory settings, the ecological factors shaping mosquito development and population dynamics in natural environments remain poorly understood. Here, we used a multi-disciplinary approach, integrating field data from Mali, laboratory experiments, and mathematical modeling, to investigate the causal relationships between climate variables and the abundance of Anopheles gambiae s.l. mosquitoes. Using convergent-cross mapping analyses an adult abundance in the Nanguilabou village, we observed that the dynamics of adult mosquito populations was driven by larval thermosensitivity. To elucidate the underlying mechanisms, we conducted experimental studies that revealed a density-dependent larval thermal response. Through mathematical modeling, we quantified the complex interplay between temperature and larval density, demonstrating that temperature and density have independent, non-synergistic effects on larval developmental speed, mortality, and pupation rates. Our findings provide a mechanistic understanding of how larval development shapes adult mosquito populations, highlighting the significance of multidisciplinary approaches in studying climate-driven mosquito population dynamics.

ecology↗

bioRxiv2022

Niche-based deterministic assembly processes strengthen the effects of β-diversity on metacommunity functioning of marine bacterioplankton

Studies at a local community () level have shown that biodiversity positively affects ecosystem functioning due to niche-based deterministic processes like resource partitioning. Extending to a metacommunity ({beta}) level, we hypothesize that {beta} diversity also positively affects metacommunity functioning. We further hypothesize that the {beta} diversity effect is stronger (more positive) when {beta} diversity is increased by deterministic/non-random assembly processes. To test the hypotheses, we collected bacterioplankton along a transect of 6 stations in the southern East China Sea in 14 cruises. All 6 stations within a cruise were regarded as a metacommunity. For any pairs of the 6 stations, the Bray-Curtis index and summed bacterial biomass were calculated to represent {beta} diversity and metacommunity functioning, respectively. We also calculated deviation of observed mean pairwise phylogenetic similarities among species from random to represent the deterministic influences of assembly processes. We found that bacterial {beta} diversity generally positively affects metacommunity functioning; however, the {beta} diversity effect varied among cruises. Cross-cruise comparison indicates that the {beta} diversity effect increased with the deterministic assembly processes selecting for phylogenetically dissimilar species. This study extends the biodiversity-ecosystem functioning research to a metacommunity level, complementing the current framework by considering community assembly in natural environments.

ecology↗

bioRxiv2021

Trade-off between competition ability and invulnerability to predation in marine microbes; protist grazing versus viral lysis effects

Trade-offs between competition ability and invulnerability to predation are important mechanisms explaining how predation promotes bacterial diversity. However, existence of these trade-offs has apparently not been investigated in natural marine bacterial communities. Here, we address this question with growth-based measurements for each marine bacterial taxon by conducting on-board dilution experiments to manipulate predation pressure and using high-throughput sequencing to assess the response of bacterial communities. We determined that bacterial taxa with a higher predation-free growth rate were accompanied with higher predation-caused mortality, supporting existence of competitiveness-invulnerability trade-off. This trade-off was stronger and more consistent under viral lysis than protist grazing. In addition, predation generally flattened out the rank-abundance distribution and increased the evenness and richness of the bacterial community. These findings supported the "Kill-the-Winner" hypothesis. All experiments supported a significant competitiveness-invulnerability trade-off, but there was substantial variation among bacterial communities in response to predation across experiments conducted in various sites and seasons. Therefore, we inferred that the Kill-the-Winner hypothesis is important but likely not the only deterministic mechanism explaining how predation shapes bacterial assemblages in natural marine systems.

ecology↗

bioRxiv2020

Contrasting species functional trait structuring of subarctic versus subtropical copepod communities

Classic niche theory assumes that species-level functional traits affect species relative fitness and thus community structuring, but empirical tests of this assumption are scarce. Moreover, recent evidence shows increasing functional over-redundancy towards the tropics, suggesting that the extent to which functional traits confer species fitness and thus impact community structuring differs across latitudes. Here, we develop a new method: comparing the frequencies of trait categories in the species-rank abundance distributions of local communities versus their frequencies in the regional average species pool. We contrasted subarctic versus subtropical copepod communities for six important traits. In subarctic communities, medium-sized and cold-water species are selected to dominate, thus traits affect relative fitness as predicted by classic niche theory. In subtropical communities, most species are small and warm-water, but these categories are not selected to dominate, suggesting that greater diversity towards the tropics results from lesser trait-based fitness differences allowing more species to coexist.

ecology↗

bioRxiv2020

Long-term warming weakens stabilizing effects of biodiversity in aquatic ecosystems

Despite the consensus that warming will affect biodiversity, alter physicochemical environments, and disrupt biological interactions, the relative importance of these key processes and how they interact to determine overall ecosystem function is poorly understood. Here, we analyze long-term (16[~]39 years) time series data from ten aquatic ecosystems and use convergent cross mapping (CCM) to quantify the hidden causal network linking species diversity, ecosystem function, and physicochemical factors. We observe that aquatic ecosystems subject to stronger warming exhibit decreased stability (larger fluctuations in phytoplankton biomass). We further show that this effect can be attributed to a weakening of stabilizing causal pathways between biodiversity, nutrient cycling, and phytoplankton biomass. Thus, rather than thinking in terms of separate factors, a more holistic view, that causally links biodiversity and the other ecosystem components, is required to understand and predict climate impacts on the temporal stability of aquatic ecosystems.

ecology↗

bioRxiv2018

Identify and predict environmental change effects on tiger mosquitos, Aedes polynesiensis

SO_SCPLOWUMMARYC_SCPLOWTo control mosquito populations for managing vector-borne diseases, a critical need is to identify and predict their response to causal environmental variables. However, most existing attempts rely on linear approaches based on correlation, which cannot apply in complex, nonlinear natural systems, because correlation is neither a necessary nor sufficient condition for causation. Appling empirical dynamic modelling that acknowledges nonlinear dynamics on nine subpopulations of tiger mosquitos from three neighbouring reef islets of the Raiatea atoll, we identified temperature, precipitation, dew point, air pressure, and mean tide level as causal environmental variables. Interestingly, responses of subpopulations in close proximity (100-500 m) differed with respect to their causal environmental variables and the time delay of effect, highlighting complexity in mosquito-environment causality network. Moreover, we demonstrated how to explore the effects of changing environmental variables on number and strength of mosquito outbreaks, providing a new framework for pest control and disease vector ecology.

ecology↗