Identifying consumer–resource population dynamics using paleoecological data

Abstract

Ecologists have long been fascinated by cyclic population fluctuations, because they suggest strong interactions between exploiter and victim species. Nonetheless, even for populations showing high-amplitude fluctuations, it is often hard to identify which species are the key drivers of the dynamics, because data are generally only available for a single species. Here, we use a paleoecological approach to investigate fluctuations in the midge population in Lake Mývatn, Iceland, which ranges over several orders of magnitude in irregular, multigeneration cycles. Previous circumstantial evidence points to consumer-resource interactions between midges and their primary food, diatoms, as the cause of these high-amplitude fluctuations. Using a pair of sediment cores from the lake, we reconstructed 26 years of dynamics of midges using egg remains and of algal groups using diagnostic pigments. We analyzed these data using statistical methods that account for both the autocorrelated nature of paleoecological data and measurement error caused by the mixing of sediment layers. The analyses revealed a signature of consumer-resource interactions in the fluctuations of midges and diatoms: diatom abundance (as inferred from biomarker pigment diatoxanthin) increased when midge abundance was low, and midge abundance (inferred from egg capsules) decreased when diatom abundance was low. Similar patterns were not found for pigments characterizing the other dominant primary producer group in the lake (cyanobacteria), subdominant algae (cryptophytes), or ubiquitous but chemically unstable biomarkers of total algal abundance (chlorophyll a); however, a significant but weaker pattern was found for the chemically stable indicator of total algal populations (β-carotene) to which diatoms are the dominant contributor. These analyses provide the first paleoecological evaluation of specific trophic interactions underlying high amplitude population fluctuations in lakes.

Increased duration of aquatic resource pulse alters community and ecosystem responses in a subarctic plant community

“…As such, we hypothesize that the centuries of midge emergence from Mývatn (Einarsson et al. ) and the repeated allochthonous deposition to land could have shifted the terrestrial system from heath dominant, as is the condition at nearby non‐midge lakes (Gratton et al. ), to one that is graminoid dominant (Raudenbush ).…”

Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production, biomass, and composition

“…The midges in turn support higher trophic levels, including fish and waterfowl. The midge species undergo large population fluctuations that have irregularly timed peaks and crashes (Einarsson et al., ), and these fluctuations are thought to be driven by consumer‐resource interactions between larvae of the dominant midge species, Tanytarsus gracilentus (Holmgren), and benthic diatoms (Einarsson, Gardarsson, Gíslason, & Ives, ; Einarsson, Hauptfleisch, Leavitt, & Ives, ; Ives, Einarsson, Jansen, & Gardarsson, ). Therefore, characterising the controls on benthic algal production is necessary for understanding the dynamics of the whole system.…”

Post‐fire vegetation and climate dynamics in low‐elevation forests over the last three millennia in Yellowstone National Park

“…Autoregressive models are simple linear models that include lagged effects in both the response variable and environmental noise (Ives et al 2010). AR models and similar autoregressive moving average (ARMA) and autoregressive integrated moving average (ARIMA) models have been widely used to model the dynamical characteristics of ecological time series (Williams et al 2003, Ives et al 2010, Einarsson et al 2016. To assess the conditions during the recruitment window, we first determined if a charcoal peak took place within the 40-100 yr prior to a pollen sample.…”