Limits...
Fractal Hypothesis of the Pelagic Microbial Ecosystem-Can Simple Ecological Principles Lead to Self-Similar Complexity in the Pelagic Microbial Food Web?

Våge S, Thingstad TF - Front Microbiol (2015)

Bottom Line: We discuss a mechanism that could be underlying the formation of repeated patterns at different trophic levels and discuss how this may help understand characteristic biomass size-spectra that hint at scale-invariant properties of the pelagic environment.If the idea of simple underlying principles leading to a fractal-like organization of the pelagic food web could be formalized, this would extend an ecologists mindset on how biological complexity could be accounted for.It may furthermore benefit ecosystem modeling by facilitating adequate model resolution across multiple scales.

View Article: PubMed Central - PubMed

Affiliation: Marine Microbial Ecology Group, Department of Biology, University of Bergen and Hjort Centre for Marine Ecosystem Dynamics Bergen, Norway.

ABSTRACT
Trophic interactions are highly complex and modern sequencing techniques reveal enormous biodiversity across multiple scales in marine microbial communities. Within the chemically and physically relatively homogeneous pelagic environment, this calls for an explanation beyond spatial and temporal heterogeneity. Based on observations of simple parasite-host and predator-prey interactions occurring at different trophic levels and levels of phylogenetic resolution, we present a theoretical perspective on this enormous biodiversity, discussing in particular self-similar aspects of pelagic microbial food web organization. Fractal methods have been used to describe a variety of natural phenomena, with studies of habitat structures being an application in ecology. In contrast to mathematical fractals where pattern generating rules are readily known, however, identifying mechanisms that lead to natural fractals is not straight-forward. Here we put forward the hypothesis that trophic interactions between pelagic microbes may be organized in a fractal-like manner, with the emergent network resembling the structure of the Sierpinski triangle. We discuss a mechanism that could be underlying the formation of repeated patterns at different trophic levels and discuss how this may help understand characteristic biomass size-spectra that hint at scale-invariant properties of the pelagic environment. If the idea of simple underlying principles leading to a fractal-like organization of the pelagic food web could be formalized, this would extend an ecologists mindset on how biological complexity could be accounted for. It may furthermore benefit ecosystem modeling by facilitating adequate model resolution across multiple scales.

No MeSH data available.


Related in: MedlinePlus

Pelagic planktonic food web organized according to size and evolutionary appearance of plankton functional types. Gy = 1 billion years before present. Viruses are not shown for simplicity but add an additional level of complexity to the trophic network within each plankton functional type, as described in the text. Note the organism size-span in this system covering several orders of magnitude. Modified from Thingstad et al. (2010).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4664636&req=5

Figure 7: Pelagic planktonic food web organized according to size and evolutionary appearance of plankton functional types. Gy = 1 billion years before present. Viruses are not shown for simplicity but add an additional level of complexity to the trophic network within each plankton functional type, as described in the text. Note the organism size-span in this system covering several orders of magnitude. Modified from Thingstad et al. (2010).

Mentions: Identifying processes found in different disciplines is an important step toward formulating unifying theories. As KtW and keystone predation are analogous concepts traditionally used to explain coexistence in microbial and macro-ecology, respectively (Våge et al., 2014), this mechanism is a unifying principle linking microbial and macro-ecology. Also, arms-race dynamics with underlying KtW mechanisms leading to increasing plankton size during the evolution of the marine microbial food web (Thingstad et al., 2010) can be understood on similar terms as what is known under “Cope's rule” in macro-ecology (Alroy, 1998; Hone and Benton, 2005); within the pelagic ecosystem, evolution of the planktonic food web is foreseen as a series of advancements in arms technology against predation during the last 3.5 billion years (Thingstad et al., 2010). Starting with heterotrophic prokaryotes, the addition of increasingly more complex organisms such as eukaryotic phytoplankton, ciliates, diatoms and copepods may be explained by antagonistic evolution where newly established predator-prey interactions drive evolution toward larger but competitively inferior prey (Thingstad et al., 2010, Figure 7). Within the pelagic microbial food web, increased body size has a high cost in terms of nutrient limitation and sinking rates as these are roughly proportional to the square of the cell radius (Tambi et al., 2009). Large organisms therefore generally loose in the competition for nutrients in diffusion limited environments and sink faster from productive surface waters. The establishment of large plankton groups must thus have been based on some novel advantage, most likely linked to selective advantage of large prey due to improved predation avoidance. Newly established prey with increased body size escaped the predation pressure of previously established predators adapted to predate on previously established, smaller prey. Increasing size of organisms over time in evolving lineages in macro-ecology is explained analogously in “Cope's rule” (Stanley, 1973; Alroy, 1998; Kingsolver and Pfennig, 2004). According to “Cope's rule,” such directional evolution can only persist when biotic factors are main drivers of selection in a relatively stable environmental setting, whereas extinction events driven by abiotic factors will disrupt this tendency (Stanley, 1973). Size-selective grazing over long periods of time in the relatively stable pelagic environment (compared to other habitats on Earth) may explain why size-structure in the planktonic food web is so clearly expressed.


Fractal Hypothesis of the Pelagic Microbial Ecosystem-Can Simple Ecological Principles Lead to Self-Similar Complexity in the Pelagic Microbial Food Web?

Våge S, Thingstad TF - Front Microbiol (2015)

Pelagic planktonic food web organized according to size and evolutionary appearance of plankton functional types. Gy = 1 billion years before present. Viruses are not shown for simplicity but add an additional level of complexity to the trophic network within each plankton functional type, as described in the text. Note the organism size-span in this system covering several orders of magnitude. Modified from Thingstad et al. (2010).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664636&req=5

Figure 7: Pelagic planktonic food web organized according to size and evolutionary appearance of plankton functional types. Gy = 1 billion years before present. Viruses are not shown for simplicity but add an additional level of complexity to the trophic network within each plankton functional type, as described in the text. Note the organism size-span in this system covering several orders of magnitude. Modified from Thingstad et al. (2010).
Mentions: Identifying processes found in different disciplines is an important step toward formulating unifying theories. As KtW and keystone predation are analogous concepts traditionally used to explain coexistence in microbial and macro-ecology, respectively (Våge et al., 2014), this mechanism is a unifying principle linking microbial and macro-ecology. Also, arms-race dynamics with underlying KtW mechanisms leading to increasing plankton size during the evolution of the marine microbial food web (Thingstad et al., 2010) can be understood on similar terms as what is known under “Cope's rule” in macro-ecology (Alroy, 1998; Hone and Benton, 2005); within the pelagic ecosystem, evolution of the planktonic food web is foreseen as a series of advancements in arms technology against predation during the last 3.5 billion years (Thingstad et al., 2010). Starting with heterotrophic prokaryotes, the addition of increasingly more complex organisms such as eukaryotic phytoplankton, ciliates, diatoms and copepods may be explained by antagonistic evolution where newly established predator-prey interactions drive evolution toward larger but competitively inferior prey (Thingstad et al., 2010, Figure 7). Within the pelagic microbial food web, increased body size has a high cost in terms of nutrient limitation and sinking rates as these are roughly proportional to the square of the cell radius (Tambi et al., 2009). Large organisms therefore generally loose in the competition for nutrients in diffusion limited environments and sink faster from productive surface waters. The establishment of large plankton groups must thus have been based on some novel advantage, most likely linked to selective advantage of large prey due to improved predation avoidance. Newly established prey with increased body size escaped the predation pressure of previously established predators adapted to predate on previously established, smaller prey. Increasing size of organisms over time in evolving lineages in macro-ecology is explained analogously in “Cope's rule” (Stanley, 1973; Alroy, 1998; Kingsolver and Pfennig, 2004). According to “Cope's rule,” such directional evolution can only persist when biotic factors are main drivers of selection in a relatively stable environmental setting, whereas extinction events driven by abiotic factors will disrupt this tendency (Stanley, 1973). Size-selective grazing over long periods of time in the relatively stable pelagic environment (compared to other habitats on Earth) may explain why size-structure in the planktonic food web is so clearly expressed.

Bottom Line: We discuss a mechanism that could be underlying the formation of repeated patterns at different trophic levels and discuss how this may help understand characteristic biomass size-spectra that hint at scale-invariant properties of the pelagic environment.If the idea of simple underlying principles leading to a fractal-like organization of the pelagic food web could be formalized, this would extend an ecologists mindset on how biological complexity could be accounted for.It may furthermore benefit ecosystem modeling by facilitating adequate model resolution across multiple scales.

View Article: PubMed Central - PubMed

Affiliation: Marine Microbial Ecology Group, Department of Biology, University of Bergen and Hjort Centre for Marine Ecosystem Dynamics Bergen, Norway.

ABSTRACT
Trophic interactions are highly complex and modern sequencing techniques reveal enormous biodiversity across multiple scales in marine microbial communities. Within the chemically and physically relatively homogeneous pelagic environment, this calls for an explanation beyond spatial and temporal heterogeneity. Based on observations of simple parasite-host and predator-prey interactions occurring at different trophic levels and levels of phylogenetic resolution, we present a theoretical perspective on this enormous biodiversity, discussing in particular self-similar aspects of pelagic microbial food web organization. Fractal methods have been used to describe a variety of natural phenomena, with studies of habitat structures being an application in ecology. In contrast to mathematical fractals where pattern generating rules are readily known, however, identifying mechanisms that lead to natural fractals is not straight-forward. Here we put forward the hypothesis that trophic interactions between pelagic microbes may be organized in a fractal-like manner, with the emergent network resembling the structure of the Sierpinski triangle. We discuss a mechanism that could be underlying the formation of repeated patterns at different trophic levels and discuss how this may help understand characteristic biomass size-spectra that hint at scale-invariant properties of the pelagic environment. If the idea of simple underlying principles leading to a fractal-like organization of the pelagic food web could be formalized, this would extend an ecologists mindset on how biological complexity could be accounted for. It may furthermore benefit ecosystem modeling by facilitating adequate model resolution across multiple scales.

No MeSH data available.


Related in: MedlinePlus