Plant height and lifespan predict range size in southern African grasses

Aluoneswi C Mashau,Sally Archibald,Caroline E R Lehmann,Gareth P Hempson,Maria S Vorontsova,Vernon Visser

doi:10.1111/jbi.14261

Abstract

AbstractAimTo understand the geographical distribution of grasses in sub‐Saharan Africa with reference to key plant traits thought to affect range size in this family (Poaceae). Specifically, to test hypotheses on the importance of plant height and lifespan in determining range size and invasion potential in the context of their evolutionary history.LocationSub‐Saharan Africa.TaxonPoaceae.MethodsThe range sizes of 757 grass species native to southern Africa were estimated for the sub‐Saharan African region from geo‐referenced herbarium records using the alpha hull function. Phylogenetic generalised least squares models and linear mixed effects models were fitted to test whether grass range size was related to plant height and lifespan. Tribe‐level relationships between range size and plant height were assessed with linear models. For species introduced to other continents, generalised linear mixed effects models were fitted to test whether invasiveness was related to native range size, plant height and lifespan. Differences in native range size among species in four invasion‐related categories were assessed with linear mixed effects models.ResultsGrass range sizes are larger for taller species and for species with shorter lifespans. The relationship between plant height and range size varies widely among tribes, with some range‐restricted tribes having a non‐significant effect on plant height. Grasses with larger native range sizes and shorter lifespans are more likely to become invasive after being introduced to other continents. Grass species introduced to other continents have larger native range sizes than those that have not, and native range size increases along the introduced‐naturalised‐invasive continuum.Main conclusionsThe increased dispersal opportunities of annual‐biannual grasses appear to have a greater positive effect on range size than do the longer generation times of perennial grasses. Grass height has and continues to be an important driver of grass biogeography, with implications for understanding the spread of certain grass tribes over the Miocene. Factors that promote large native range sizes are also likely to increase the probability of a species becoming invasive.

Highlights

The geographical area a species occupies is a complex product of environmental, competitive, geographic and biological factors (Brown et al, 1996; Gaston, 2003; Morueta-Holme et al, 2013; Sheth et al, 2020)
Human activities impact all parts of the Earth, and range size is important for assessing extinction risk and adaptation capacity (Manne et al, 1999; Staude et al, 2020) and, the potential for species to become naturalised and invasive when introduced to new areas (Hui et al, 2011; Procheş et al, 2012; Pyšek et al, 2009)
Grass species range sizes were strongly related to both plant height and lifespan

Summary

Introduction

The geographical area a species occupies is a complex product of environmental, competitive, geographic and biological factors (Brown et al, 1996; Gaston, 2003; Morueta-Holme et al, 2013; Sheth et al, 2020). Large range sizes can be a consequence of low speciation rates (Gaston, 1998) Each of these processes such as dispersal potential, establishment success, and speciation rates are the result of multiple organismal traits, with range size an emergent property of these interacting processes (Figure 1). Once introduced, factors shaping plant reproduction and dispersal characteristics are likely as important as habitat suitability and establishment success in determining whether a species will become invasive (Pyšek et al, 2009). Supporting these ideas, Hui et al (2011) demonstrated that invasive Acacias are more likely to have larger native range sizes in Australia than non-invasive species

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