Endangered Plants in Novel Urban Ecosystems Are Filtered by Strategy Type and Dispersal Syndrome, Not by Spatial Dependence on Natural Remnants

Greg Planchuelo,Moritz von der Lippe,Ingo Kowarik

doi:10.3389/fevo.2020.00018

Abstract

Understanding the contribution of cities to nature conservation is gaining increasing importance with a globally accelerating urbanization and requires insights into the mechanisms that underlie urban distribution patterns. While a considerable number of endangered plant species have been reported for cities, the spatial dependence of populations of these species on natural remnants versus anthropogenic ecosystems is critically understudied due to deficiencies in population distribution data. To which extent endangered species in anthropogenic ecosystems spatially rely on natural remnants is thus an open question. We used a unique dataset of 1,742 precisely mapped populations of 213 endangered plant species in the city of Berlin and related these point data to habitat patches that had been assigned to natural remnants, hybrid ecosystems and novel ecosystems according to the novel ecosystem approach. By applying recent techniques in point pattern analysis (Ripley's K function, cross K function, cross pair correlation function) we unraveled the spatial dependence of the populations towards the different ecosystem types. Moreover, we tested how plant traits related to plant strategy and dispersal filter for species assemblages across ecosystems. Differentiating populations on anthropogenic sites revealed that populations in hybrid ecosystems spatially depended on natural remnants, but populations in novel ecosystems (i.e. more than a third of all populations) surprisingly didn’t. A conditional inference tree showed that endangered plant species in novel ecosystems are filtered for ruderal strategy type and wind dispersal syndrome, while competitive and stress-tolerant species were assigned to natural remnants. Our results highlight the importance of conserving natural remnants as habitats and seed sources of endangered plants. Yet novel urban ecosystems can support many populations of endangered plant species beyond the adjacency to natural remnants, with hybrid ecosystems likely acting as stepping stones. This indicates a specific contribution of urban ecosystems to biodiversity conservation. Since different filters modulate the species assemblages of different ecosystem types, novel urban ecosystems are not supposed to substitute fully the habitat functions of natural remnants. Our study thus highlights promising opportunities for involving the total range of urban ecosystem types into urban conservation approaches.

Highlights

Cities can harbor a high biological richness (Kühn et al, 2004; Aronson et al, 2014), including a considerable richness of endangered plant species (Schwartz et al, 2002; Lawson et al, 2008; Lenzen et al, 2009; Shwartz et al, 2014; Ives et al, 2016; Kowarik and von der Lippe, 2018; Planchuelo et al, 2019)
Results from the cross L function show that from the populations located in anthropogenic ecosystems, only those in hybrid ecosystems are spatially correlated to natural remnant ecosystems (Figure 3A, green line), as the observed curve of the point process crosses outside of the boundaries of the global envelope of the null model (Baddeley et al, 2014)
Endangered species assigned to a ruderal strategy type (r, rc, rs, rcs) and with anemochory as main dispersal syndrome were exceedingly represented in novel ecosystems (Node 3, Figure 4)

Summary

Introduction

Cities can harbor a high biological richness (Kühn et al, 2004; Aronson et al, 2014), including a considerable richness of endangered plant species (Schwartz et al, 2002; Lawson et al, 2008; Lenzen et al, 2009; Shwartz et al, 2014; Ives et al, 2016; Kowarik and von der Lippe, 2018; Planchuelo et al, 2019). Urban areas in Australia, for example, host 30% of the country’s endangered plant species (Ives et al, 2016), with some of them occurring today exclusively in urban environments (Soanes and Lentini, 2019) While these studies indicate a high potential of cities to contribute to biodiversity conservation at a global scale (McKinney, 2008; Kowarik, 2011), survival in urban environments is a challenge for many species as demonstrated by establishment failures (Kowarik and von der Lippe, 2018), extinction debts (Hahs and McDonnell, 2014) and completed extinctions (Knapp et al, 2010; Duncan et al, 2011). This is an essential gap of knowledge because responses of large species sets to urbanization cannot be translated to endangered species, as indicated by contrasting species’ traits that have gone extinct or, alternatively, persist in cities (Knapp et al, 2010; Duncan et al, 2011; Williams et al, 2015)

Methods

Results

Conclusion