Temperature‐dependence of minimum resource requirements alters competitive hierarchies in phytoplankton

Abstract

Resource competition theory is a conceptual framework that provides mechanistic insights into competition and community assembly of species with different resource requirements. However, there has been little exploration of how resource requirements depend on other environmental factors, including temperature. Changes in resource requirements as influenced by environmental temperature would imply that climate warming can alter the outcomes of competition and community assembly. We experimentally demonstrate that environmental temperature alters the minimum light and nitrogen requirements – as well as other growth parameters – of six widespread phytoplankton species from distinct taxonomic groups. We found that species require the most nitrogen at the highest temperatures while light requirements tend to be lowest at intermediate temperatures, although there are substantial interspecific differences in the exact shape of this relationship. We also experimentally parameterize two competition models, which we use to illustrate how temperature, through its effects on species’ traits, alters competitive hierarchies in multispecies assemblages, determining community dynamics. Developing a mechanistic understanding of how temperature influences the ability to compete for limiting resources is a critical step towards improving forecasts of community dynamics under climate warming.

Diversity and temperature indirectly reduce CO2 concentrations in experimental freshwater communities

“…The photosynthetic responses of individual phytoplankton species differ in their sensitivity to temperature and to species interactions. In particular, warming can alter community dynamics through changes to the relative competitiveness of individual phytoplankton species (Lewington-Pearce et al 2019). Some species benefit from increases in temperature and diversity if conditions favour their individual temperature optima (Huertas et al 2011;Lewington-Pearce et al 2019;Schabhüttl et al 2013).…”

“…In particular, warming can alter community dynamics through changes to the relative competitiveness of individual phytoplankton species (Lewington-Pearce et al 2019). Some species benefit from increases in temperature and diversity if conditions favour their individual temperature optima (Huertas et al 2011;Lewington-Pearce et al 2019;Schabhüttl et al 2013). Other taxa pushed away from their temperature optima can go locally extinct or experience competitive displacement from dominant species (Lewington-Pearce et al 2019;Schabhüttl et al 2013).…”

“…Some species benefit from increases in temperature and diversity if conditions favour their individual temperature optima (Huertas et al 2011;Lewington-Pearce et al 2019;Schabhüttl et al 2013). Other taxa pushed away from their temperature optima can go locally extinct or experience competitive displacement from dominant species (Lewington-Pearce et al 2019;Schabhüttl et al 2013). This also stands true for the carbon capture abilities of individual phytoplankton species.…”

Warming of aquatic ecosystems disrupts aquatic–terrestrial linkages in the tropics

“…Asymmetric thermal responses among species and functional groups alter community structure and ecosystem function through shifting biotic interactions (Shurin et al, 2012). For instance, increasing predation pressure with warming (Amundrud & Srivastava, 2019;Romero et al, 2018) alters the relative strength of top-down and bottom-up processes (Kratina et al, 2012), while changes in competitive outcomes (Lewington-Pearce et al, 2019) can shift the community size spectra towards a prevalence of small-bodied organisms (Gardner et al, 2011). In aquatic ecosystems, this directly affects organisms which break down terrestrial detritus (Cole et al, 2006), and animals with aquatic larval and terrestrial adult life stages that transfer resources between ecosystems (Recalde et al, 2016).…”

Body size and shape responses to warming and resource competition

“…Whereas previous work has focused on responses to abiotic variables, competition is a fundamental driver of community structure, which alters resource availability (Fox, 2002), and interacts with environmental temperature (Jiang & Morin, 2004; Lewington‐Pearce et al., 2019). As higher temperatures tend to increase metabolic rates up to the thermal optimum of an organism (Brown et al., 2004), warming can increase per capita competitive intensity (Jiang & Morin, 2004) and indirectly influence both body size and shape through reducing resource availability.…”