I am a PhD student with Marissa Baskett at UC Davis since 2014. I am most excited about using ecological models and statistics to understand the dominant mechanisms governing the dynamics of aquatic systems. My research focuses firstly on exploring how processes commonly found in nature like nontrophic interactions, dispersal, and environmental stochasticity, affect community dynamics using carefully parameterized, system-specific models. The other, equally important, theme of my research is applying these and other existing ideas in theoretical and quantitative ecology to long-term datasets, using model selection and statistics to elucidate the deterministic backbone underlying the observed population or community dynamics. As lakes, streams, and coastal marine systems are hotspots of both human activity and biotic diversity, figuring out how these systems work to facilitate their management and conservation drives my research.
CAN OPEN FORESTS COLLAPSE TO URCHIN BARRENS? We have prominent examples of alternative ecosystem states in systems largely closed to dispersal, such as lakes and grasslands. On the other hand, whether local dynamics in coastal systems can abruptly shift between alternatively stable states is questionable given that most recruits originate from subpopulations tens or hundreds of kilometers away. To explore this question, we built a simple tritrophic model of giant kelp, purple urchins, and predators in a local area, which exhibits two stable states - a forest or an urchin barren - when closed (no external recruitment). Indeed, we find that when a moderate proportion (20-30%) of new urchin and predator recruits originate from nearby kelp forests, this prevents predator extinction and the formation of barrens. However, in strongly open systems, urchin recruitment is sufficiently high to overcome natural mortality and predation, and urchin barrens may again occur. Overall, the levels of fishing of predators and openness in urchin recruitment have a greater effect on the occurrence of urchin barrens than openness in predator recruitment. These results can help determine areas where kelp forest communities are more prone to an abrupt collapse, and where management can help alleviate this threat by limiting predator fishing levels. Karatayev, V.A., and Marissa L. Baskett
Below you can find some of my recently completed or ongoing (non-thesis) projects:
GREAT LAKES: CAN HABITAT-SPECIFIC DEMOGRAPHY OF INVASIVES REGULATE THEIR LARGE-SCALE IMPACTS? We often quantify the ecological impacts of invasive species based on the strength of their presence in their environment. Dreissena spp. mussels are the world's most invasive freshwater species which energetically deplete open-water food webs by filter feeding on phytoplankton. Since 1986, they have colonized the vast majority of benthic habitats of the Great Lakes, typically attaining high densities across 10-200m depths. Whereas the immense ecosystem-scale effects of these species have been predicted based on individual growth rates in shallow water, growth and mortality rates appear to be drastically reduced in habitats below the thermocline (>90% of total benthic area in the lakes). I'm aiming to attain spatially explicit growth and longevity estimates (which together reflect the species' impacts on phytoplankton) by fitting integral projection models to population size structure observed across hundreds of sites. Integrating these estimates with the spatial distribution of mussel densities may offer an insight into the extent to which the ability to live in a wide range of environments, which makes these invaders so successful, might also limit their system-wide ecological impacts. Karatayev, V.A., Sebastian Schreiber (UC Davis), Thomas Nalepa (University of Michigan), Alexander Karatayev, Lyubov Burlakova (Great Lakes Center), and others
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RACING THROUGH LIFE: MATURATION RATE PLASTICITY REGULATES OVERCOMPENSATION AND INCREASES PERSISTENCE Induced changes in the demographic traits of harvested populations produce ecological responses to mortality that would not be predicted by traditional models that assume such traits to be fixed. Such plasticity in maturation rates, which positively affect the population growth rate, can be strong in intensely harvested populations. We explore how density-dependent maturation rates affect the dynamics of populations which exhibit overcompensation, a scenario in which population control through harvest results in an increase in abundance. We found that such plasticity in maturation rates dampens or eliminates overcompensation (A), which could account for the relatively few reported cases of strong overcompensation. On the other hand, density dependence in maturation greatly amplifies the harvest effort required to reduce or collapse populations with low survival rates (B). This effect can frustrate efforts to control or eradicate invasive or nuisance populations, and may also inform management of ecologically and/or economically important populations. Karatayev, V.A., Clifford E. Kraft (Cornell), and Elise F. Zipkin (Michigan S.U.) Ecosphere October 2015
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EUTROPHICATION AND DREISSENA INVASION AS DRIVERS OF LAKE BIODIVERSITY Lakes are known to exhibit alternative ecosystem states, most prominently turbid (phytoplankton-dominated) vs. clear-water (macrophyte-dominated) states. Although several communities are known to differ distinctly between these states, few studies report a connection between alternate states and changes in system-wide biodiversity. Thanks to detailed studies spanning the past century on the diverse (~30 species) mollusc assemblage of Oneida Lake, we were able to associate a switch to the eutrophication-induced turbid phase with both a 95% decline in abundance and a 40% reduction in lakewide biodiversity of native grazing molluscs. These changes were markedly reversed following the invasion of filter-feeding dreissenid mussels. The species of grazing molluscs we studied are both a key link between the benthic and pelagic communities, also may be representative of the overall changes experienced by the benthic communities of aquatic systems facing increased nutrient loading. Karatayev VA, Karatayev AY, Burlakova LE, Rudstam LG (2014). PLoS ONE 9(7): e101388.
LAKEWIDE DOMINANCE DOES NOT PREDICT THE POTENTIAL FOR SPREAD OF DREISSENIDS Lakewide dominance does not predict the potential for spread of dreissenids Zebra and quagga mussels (Dreissena sp.) are among the most invasive aquatic species in the world. These cogeners exhibit an interesting case of competition-colonization tradeoff: quagga mussels outcompete zebras within lakes due to a higher energetic efficiency, while zebra mussels have colonized many times more waterbodies. As few studies have attempted to address the latter pattern, we looked at dreissenid presence on recreational boats (the main vector of dreissenid spread across North America) and similar substrates in marinas on the Lower Great Lakes. It turns out that although quagga mussels comprise >95% of the dreissenid abundance in both lakes, zebras remain in shallow-water refuges, and are often more abundant and grow faster on recreational boats. We attribute this trend to the shell morphology and stronger attachment strength of zebra mussels - two small physiological differences which contribute to a dramatic difference in the spread of these cogeners. Karatayev, V. A., A. Y. Karatayev, L. E. Burlakova, and D. K. Padilla. 2013. Journal of Great Lakes Research 39: 622-629. PDF