1,345 research outputs found
Critical turbulence revisited: The impact of submesoscale vertical mixing on plankton patchiness
By supplying nutrients to the ocean surface, submesoscale vertical motions can have a strong impact on phytoplankton growth and phytoplankton distributions. To study this impact, we model a phytoplankton population in a baroclinically unstable submesoscale eddy using a phytoplankton model coupled to a three-dimensional hydrodynamic model. In the eddy, strong vertical transports are generated as a consequence of baroclinic instability. The resulting plankton distributions turn out to depend strongly on the light intensity and local vertical transport. To analyze these distributions in detail, we use more idealized coupled hydrodynamic-biological models and we extend the critical turbulence concept to three dimensions
Modes of Growth in Dynamic Systems
Regardless of a system's complexity or scale, its growth can be considered to
be a spontaneous thermodynamic response to a local convergence of down-gradient
material flows. Here it is shown how growth can be constrained to a few
distinct modes that depend on the availability of material and energetic
resources. These modes include a law of diminishing returns, logistic behavior
and, if resources are expanding very rapidly, super-exponential growth. For a
case where a system has a resolved sink as well as a source, growth and decay
can be characterized in terms of a slightly modified form of the predator-prey
equations commonly employed in ecology, where the perturbation formulation of
these equations is equivalent to a damped simple harmonic oscillator. Thus, the
framework presented here suggests a common theoretical under-pinning for
emergent behaviors in the physical and life sciences. Specific examples are
described for phenomena as seemingly dissimilar as the development of rain and
the evolution of fish stocks.Comment: 16 pages, 6 figures, including appendi
Cross-ecosystem effects of terrestrial predators link treefrogs, zooplankton, and aquatic primary production
Predators can directly or indirectly shape food webs through a combination of consumptive and non-consumptive effects. Yet, how these effects vary across natural populations and their consequences for adjacent ecosystems remains poorly resolved. We examined links between terrestrial predators and aquatic ecosystems through their effects on a locally abundant amphibian, the red-eyed treefrog (Agalychnis callidryas), which has arboreal eggs (heavily predated by snakes and wasps) and aquatic larvae; embryos can escape terrestrial threats by hatching at an earlier age and smaller size. Our multi-site field survey indicates that in natural populations, the relative contributions of these consumptive and non-consumptive effects of predators can be substantial and remarkably similar. However, in mesocosms where we experimentally mimicked these predator effects, changes in the density and initial hatching age of tadpoles carried distinct consequences for aquatic food webs. Density-dependent growth resulted in peak tadpole biomass at intermediate densities (reflecting intermediate predation), and early-hatched tadpoles grew 16% faster and produced 26% more biomass than their late-hatched counterparts. These changes in tadpole growth and size differentially affected zooplankton communities, and the production and stability of phytoplankton. Together, these results illustrate multiple pathways through which predators in one ecosystem can modulate the structure of adjacent food webs
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