Food webs provide a map of how species are connected in ecosystems, and thus help describe complexity, species interactions, and functioning in ecosystems. Parasites are not often considered in food webs, but when they have been explicitly included, they make large contributions to diversity, biomass, and complexity, changing food web structure . Trophically-transmitted parasites track food chains in completing their life cycles, so can provide valuable information about a species of interest’s diet and predators. Top-down interactions can structure ecosystems, but are subject to change with habitat structure, food-web context, and environmental conditions. Parasites especially can be unseen components of food webs that can impact fisheries via mortality and reduced market value. Thus, accurate food webs and knowledge of parasitic interactions are directly useful to species and ecosystem management.
My research program in marine ecology uses food webs as a tool to provide mechanistic understanding of marine ecosystems. I have a strong foundation in natural history and field ecology, and my projects employ field experiments, observational studies, network analysis, statistical models, and synthesis of large datasets. I use these tools to build food webs that are ecologically relevant, and then use these food webs to generate testable hypotheses about ecosystem function.
My research program in marine ecology uses food webs as a tool to provide mechanistic understanding of marine ecosystems. I have a strong foundation in natural history and field ecology, and my projects employ field experiments, observational studies, network analysis, statistical models, and synthesis of large datasets. I use these tools to build food webs that are ecologically relevant, and then use these food webs to generate testable hypotheses about ecosystem function.
Food webs and parasites
In my past research, I explicitly incorporated the often-overlooked interactions that make up the bulk of complexity and energetic exchanges in ecosystems, such as those involving parasites and other small invertebrates. Working with Armand Kuris and Kevin Lafferty at UCSB, I used extensive sampling and systematic literature review to construct a food web for the kelp forests of the Santa Barbara Channel, CA (Morton et al. 2021). The food web is resolved to the species level for most nodes, and includes free-living and parasitic species, which allowed me to examine the roles of parasites in the system. After controlling for network size, adding parasites increased food-chain length and complexity, consistent with other food webs (Morton and Lafferty, in review). However, kelp-forest parasites were more diverse and specialized than other systems, which reduced network connectance. I am currently examining how food-web stability and structure change with temperature. |
Graph of the kelp-forest food web without (a) and with (b) parasites, showing the magnitude of the node list, density of links in the network, and increase in network size with the inclusion of parasites. Blue nodes are free-living taxa, red nodes are parasites, green are autotrophs, and brown are detritus. Each node represents a life stage of a species, and arrows point from consumers to resources. Created in igraph in R. Credit: Morton et al. 2021; https://doi.org/10.1038/s41597-021-00880-4; Creative Commons License: http://creativecommons.org/licenses/by/4.0/
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Role of habitat
Spatially complex habitats can structure ecosystems by altering trophic interactions as well as organism recruitment. I found that certain invertebrate taxa showed patterns of settlement consistent with a filtering effect of the kelp forest, either due to current modification, predation, or reduced larval supply as larvae settled out of the plankton (Morton and Anderson 2013). The patterns lead me to consider the scale at which organisms are influenced by habitat structure. Using a field experiment, we found that spatial configuration of artificial habitat patches had an effect on settling fishes (Morton and Shima 2013). On a small scale, larger contiguous habitat patches had higher densities of newly settled fish than smaller or large sparse ones, even when the fine-scale habitat quality was the same. The organisms in both of these studies have bipartite life histories, and recruitment to adult habitats was influenced by the spatial arrangement of the habitat itself. However, even when a species reproduces within a given system, they may be influenced by forces operating across multiple scales. We found evidence for this in an additional study of amphipods (which lack a pelagic larval stage) within kelp forests. Amphipods tended to synchronously fluctuate in abundance across a large reef system, suggesting abundances were controlled by forces operating at regional scales, rather than by the density of kelp locally (Morton et al. 2016). These results underscore how scale is central to ecology, and how layers of processes influence species abundance. |
Linking trophic structure to ecosystem dynamics
My future work seeks to examine the relationships between the food webs, primary production and environmental variables, to gain a mechanistic understanding of ecosystem dynamics across spatial and temporal scales.
My future work seeks to examine the relationships between the food webs, primary production and environmental variables, to gain a mechanistic understanding of ecosystem dynamics across spatial and temporal scales.