Selective feeding behaviour of key free-living protists: avenues for continued study

Abstract

Phagotrophic protists are diverse and abundant in aquatic and terrestrial environments, making them fundamental to the transfer of matter/energy within their respective food webs. Recognising their grazing impact is essential to evaluate the role of protists in ecosystems, and this includes appreciating prey selectivity. Efforts have been made by groups and individuals to understand selective grazing behaviour by protists: many approaches and perspectives have been pursued, not all of which are compatible. This article, which is not a review, is the product of our discourse on this subject at the SAME 10 meeting. It is the work of individuals, assembled for their breadth of backgrounds, approaches, views, and expertise. Firstly, to communicate ideas and approaches, we develop a framework for selective feeding processes and suggest 6 steps: searching, contact, capture, processing, ingestion, digestion. We then separate study approaches into 2 categories: (1) those examining whole organisms at the community, population, and individual levels, and (2) those examining physiology and molecular attributes. Finally, we explore general problems associated with the field of protistan selective feeding (e.g. linking food selection into food webs and modeling). We do not present all views on any one topic, nor do we cover all topics; instead, we offer opinions and suggest avenues for continued study. Overall, this paper should stimulate further discourse on the subject and provide a roadmap for the future.

Some Mixotrophic Flagellate Species Selectively Graze on Archaea

“…The significance of predation on bacterial activity and community structure in natural aquatic systems has been demonstrated (10,(37)(38)(39)(40). Consequently, effort is currently placed on understanding the details and dynamics of grazing by protists (11). From laboratory experiments, evidence exists that certain taxa feed selectively (41,42).…”

“…Cell size and grazing pressure. Protist prey selection may occur at various feeding steps, namely, capture, prey processing, ingestion, and digestion (11,43). Prey size is a trait that is easy to measure.…”

“…General selection mechanisms have been identified (11). However, the current view is still mainly based on laboratory data, using readily growing species (12).…”

Trait- and size-based descriptions of trophic links in freshwater food webs: current status and perspectives

“…For predators, the entire process can be divided into four main stages: encounter with prey, attack, handling (ingestion), and digestion (Jürgens and Matz, 2002;Montagnes et al, 2008). From the prey perspective, the main stages include encounter, escape from attack and escape after being caught by the predator (Greene, 1983).…”

“…Moreover, there is clearly room for multivariate descriptions of food webs and validation of existing theory (Osenberg and Mittelbach, 1989;Hildrew et al, 2007;Montagnes et al, 2008;Petchey et al, 2008;Ings et al, 2009;Rossberg et al, 2009;Jacob et al, 2011) despite the enormous success of purely size-based studies in aquatic ecology. Even if we could define a single abstract feeding niche to characterize trophic links in a food web, body size may not correlate strongly with the niche parameters (Williams et al, 2010).…”