Controls on niche stability in geologic time: congruent responses to biotic and abiotic environmental changes among Cincinnatian (Late Ordovician) marine invertebrates

Abstract

The set of environmental conditions under which a taxon can survive and maintain viable populations, known as the ecological niche, is a fundamental determinant of a taxon's distribution. Because of the central importance of ecological niches, they have been assumed to remain relatively stable during intervals of morphological stasis. However, the assumption of niche stability has rarely been tested directly with fossil data spanning multiple temporal intervals. Thus, the conditions under which this assumption is likely to be accurate are not well understood. In this study, we use ecological niche modeling (ENM) to reconstruct the ecological niche for 11 genera of marine benthos (crinoids, trilobites, molluscs, bryozoans, and corals) from the Type Cincinnatian Series (Late Ordovician, Katian Stage) across nine temporal intervals spanning approximately three million years. This interval includes both abiotic environmental change (gradual sea-level fall) and biotic change (rapid pulses of the Richmondian Invasion), thus allowing the relative effect of different environmental perturbations to be constrained. A previous symmetrical analysis of niche stability of brachiopod species recovered an increase in niche evolution following the Richmondian Invasion. Herein we test the generality of the brachiopod pattern within the community. Niche stability was evaluated in geographic space, ecological space, and niche parameter space. Niche stability varied through time; during the Pre-Invasion interval, taxa exhibited niche stability during gradual shallowing of sea level in the basin, whereas niche evolution became more common during the Richmondian Invasion. Taxa adjusted to the increased competition by altering aspects of their niche. Notably, surviving taxa contracted their niche into a subset of their previous niche parameters. This represents an adaptive response to increased competition for resources with the newly established invader taxa, and it was employed most successfully by generalist taxa. Patterns of niche evolution were congruent between clades, among feeding styles, and across taxonomic levels.

When and how do species achieve niche stability over long time scales?

“… Summary of the weighted percent geographic overlap and environmental parameter similarity data through time. Patterns are congruent between the species‐level brachiopod data of Malizia and Stigall () and the cross‐faunal genus‐level data of Brame and Stigall (). The geographic overlap percentage declines significantly between the pre‐invasion and invasion intervals, whereas environmental parameter similarity statistically increases between the pre‐invasion and invasion intervals.…”

“…Combined, the analyses of Malizia and Stigall ()and Brame and Stigall () generated 111 niche models with an average AUC value of 0.80 (range 0.70 to 1.0). Although critiques of AUC as an accuracy measure have been raised (Peterson et al , Jiménez‐Valverde ), it remains a widely reported non‐threshold based metric, and the recovered values indicate good model fit to the data.…”

“…In geographic space, taxa exhibit high percent overlap between original and forward‐projected distribution models during the pre‐invasion interval, but geographic overlap declines following the Richmondian invasion. Geographic overlap values for the brachiopod species‐level dataset of Malizia and Stigall () and the multi‐phyla genus‐level dataset of Brame and Stigall () for each of the pre‐invasion, invasion, and post‐invasion intervals are statistically indistinguishable (p = 0.505, 0.638, and 0.433, respectively). The combined data indicate that geographic overlap is high during the pre‐invasion interval (mean = 80.6%) and is reduced during the invasion and post‐invasion intervals (mean = 66.8 and 62.3%, respectively) (Supplementary material Appendix 1).…”

“…The Maxent algorithm (Phillips et al ) was used to generate ecological niche models for all taxa in each time slice with greater than 7 discrete points in a temporal interval as detailed in Malizia and Stigall () and Brame and Stigall (). Maxent ver.…”

Phylogenetic paleobiogeography of Late Ordovician Laurentian brachiopods; pp. 189–194

“…Invasive taxa also included members of all trophic levels from pelagic predators to sessile benthos. The introduction of these new taxa caused a fundamental rearrangement of the community structure which had been stable for nearly 5 million years before the invasion (Patzkowsky & Holland 2007) and resulted in niche evolution among both native and incumbent species (Brame & Stigall 2014). …”