Plant dispersal syndromes are unreliable, especially for predicting zoochory and long‐distance dispersal

Abstract

Plant dispersal syndromes are allocated based on diaspore morphology and used to predict the dominant mechanisms of dispersal. Many authors assume that only angiosperms with endozoochory, epizoochory or anemochory syndromes have a longdistance dispersal (LDD) mechanism. Too much faith is often placed in classical syndromes to explain historical dispersal events and to predict future ones. What is usually recorded as the 'endozoochory syndrome' is in reality a 'frugivory syndrome' and this has often diverted attention from endozoochory by non-frugivores (e.g. waterbirds and large herbivores) that disperse a broad range of angiosperms, for which they likely provide the maximum dispersal distances. Neither the endozoochory nor the epizoochory syndromes provide helpful predictions of which plants non-frugivores disperse, or by which mechanism. We combined data from previous studies to show that only 4% of European plant species dispersed by ungulate endozoochory belong to the corresponding syndrome, compared to 36% for ungulate epizoochory and 8% for endozoochory by migratory ducks. In contrast, the proportions of these species that are assigned to an 'unassisted syndrome' are 37, 31 and 28%, respectively. Since allocated syndromes do not adequately account for zoochory, empirical studies often fail to find the expected relationship between syndromes and LDD events such as those underlying the colonization of islands or latitudinal migration rates. We need full incorporation of existing zoochory data into dispersal databases, and more empirical research into the relationship between plant traits and the frequency and effectiveness of different dispersal mechanisms (paying attention to unexpected vectors). Acknowledging the broad role of non-frugivores in facilitating LDD is crucial to improve predictions of the consequences of global change, such as how plant distributions respond to climate change, and how alien plants spread. Networks of dispersal interactions between these vertebrates and plants are a vital but understudied part of the Web of Life.

Trade of commercial potting substrates: A largely overlooked means of the long-distance dispersal of plants

“…The ability of seeds to survive passing through the digestive tract of animals is also a critical factor, which is confirmed by the fact that species that germinated from the substrate samples typically had small, persistent seeds, which traits generally promote gut passage and endozoochorous dispersal (e.g., Albert et al 2015, Picard et al 2016. As most of the species we detected in the substrates do not have specialized structures for long-distance dispersal (e.g., special structures for anemochorous or zoochorous dispersal, see Correira et al 2018or Chen et al 2020, our findings support the notion that dispersal syndromes are inadequate for predicting plant species' ability for LDD (Green et al 2021).…”

Functional Traits Drive Dispersal Interactions Between European Waterfowl and Seeds

“…Dispersal by animal vectors (zoochory) provides longer distance dispersal in comparison to abiotic vectors (Bullock et al, 2017), with migratory birds able to provide extreme dispersal distances (Popp et al, 2011;Viana et al, 2016;Viana, 2017). These birds mainly disperse seeds via gut passage (endozoochory), yet their importance for plants lacking a fleshy-fruit has been underestimated because it is ignored by widely used "dispersal syndromes" (Green et al, 2021). Many of the migratory bird species are waterbirds, which are important for the dispersal of a broad range of both aquatic and terrestrial plants between habitat patches, often facilitating dispersal at extreme distances of >100 km (Green et al, 2016(Green et al, , 2021Viana et al, 2016;Martín-Vélez et al, 2021).…”

“…These birds mainly disperse seeds via gut passage (endozoochory), yet their importance for plants lacking a fleshy-fruit has been underestimated because it is ignored by widely used "dispersal syndromes" (Green et al, 2021). Many of the migratory bird species are waterbirds, which are important for the dispersal of a broad range of both aquatic and terrestrial plants between habitat patches, often facilitating dispersal at extreme distances of >100 km (Green et al, 2016(Green et al, , 2021Viana et al, 2016;Martín-Vélez et al, 2021). The waterbird group best known for seed dispersal is that of the waterfowl (Anatidae: ducks, swans and geese) (Green et al, 2016(Green et al, , 2021Soons et al, 2016).…”

Understanding the relationship between dispersal and range size

“…Firstly, studies differ in their dispersal 'definitions' and therefore also differ in which phenotypic traits are considered to be associated to dispersal ability. Which dispersal-related traits to choose is not a trivial question, particularly because dispersal and dispersal distance are emergent properties (complex traits) resulting from the interactive effects of various dispersalrelated traits (e.g., morphology, physiology, behavioural and life history traits), which are highly dependent on the type of organism studied (Ronce 2007 Green et al 2021). Moreover, dispersal can occur at different life stages (e.g., seeds, eggs, juveniles, adults), it is composed by three phases including departure (i.e., decision to leave the old habitat), transfer (i.e., displacement from the old to a new habitat) and settlement (i.e., arrival and settlement in the new habitat), and can be shaped by external factors and evolve (Ronce 2007, Matthysen 2012.…”