Elsevier

Fungal Ecology

Volume 13, February 2015, Pages 77-82
Fungal Ecology

Local dispersal dynamics determine the occupied niche of the red-listed lichen Seirophora villosa (Ach.) Frödén in a Mediterranean Juniperus shrubland

https://doi.org/10.1016/j.funeco.2014.08.008Get rights and content

Highlights

  • In the studied population of the lichen S. villosa mature thalli were rare.

  • S. villosa showed a very limited propagation ability.

  • The effect of habitat filtering is negligible.

Abstract

The red-listed lichen Seirophora villosa is associated with undisturbed coastal dune systems dominated by Juniperus spp. The clustered distribution of this species suggests that propagative traits may be responsible for its conservation status. We tested whether the local distribution of an S. villosa population under undisturbed conditions is limited by habitat filtering or by low dispersal fitness. Using Strip Adaptive Cluster Sampling, we estimated the size of one of the largest undisturbed Italian populations of S. villosa. We considered the abundance of both mature and juvenile thalli in relation to geographical and environmental spaces. Multiple regression on distance matrices models were in accordance with the hypothesis that S. villosa is occupying only a small portion of its colonizable niche because of a very limited propagation ability. Apart from the co-occurrence of mature thalli, the presence of juvenile thalli was independent of pure spatial and environmental factors.

Introduction

Epiphytic lichens are an ecologically important component of coastal Juniperus habitats, which are characterized by assemblages of predominantly Mediterranean-distributed species restricted to coastal ranges (Nimis and Schiavon, 1986). One such epiphytic lichen, Seirophora villosa, is a red-listed macrolichen (Nascimbene et al., 2013) strictly associated with dune environments such as coastal Juniperus shrublands (Natura 2000 priority habitat code 2250*).

These habitats are presently threatened worldwide owing to various anthropogenic pressures, such as urban coastal development, tourism, habitat fragmentation, alien species introduction and coastal erosion (Mclachlan and Brown, 2006, Picchi, 2008, Prisco et al., 2012, Bertacchi and Lombardi, 2014).

The distribution of S. villosa is spatially clustered on both large and local scales (Frödén and Lassen, 2004). The large-scale clustering is mainly due to the effect of habitat fragmentation caused by anthropogenic and natural disturbances such as tourism pressure or dune erosion (Benesperi et al., 2013). On a local scale, the clustered distribution of S. villosa is purportedly driven by both environmental filtering and the species' dispersal capability as previously reported for other epiphyte species (Öckinger et al., 2005, Schei et al., 2012). However, the importance of different predictors seems to vary with spatial scale (McGill, 2010).

Dispersal is a process fundamental for the persistence and dynamics of a population (Levin et al., 2003). Its relevance in shaping population distribution is particularly important in organisms whose habitats exhibit spatiotemporal dynamics and in patch-tracking organisms, such as several epiphytic lichens (Snäll et al., 2005, Werth et al., 2006).

The recruitment of new individuals in lichen populations depends on two non-mutually exclusive processes (Werth et al., 2006): dispersal limitation, i.e., a limited availability of propagules in a given habitat (Öckinger et al., 2005, Belinchón et al., 2009), and establishment limitation, i.e., the inability of young individuals to become established in a given habitat due to interactions with biotic and/or abiotic factors. This issue recurs in epiphytic communities independently by the colonized habitat. For example, Schei et al. (2012) showed that both local dispersal and environmental conditions influence the spatial distribution and abundance of epiphytic lichen species of the Lobarion community at fine spatial scales, in contrast with the assumption of McGill (2010) who suggests that microclimate and dispersal are more important than habitat-related factors at scales < 102 m.

According to metapopulation theory, both local habitat availability and habitat isolation are important in determining a species' distribution (Hanski, 1999), so that sometimes species may not be able to colonize all suitable habitat because they cannot disperse to isolated habitat fragments (Johansson and Ehrlén, 2003). The abiotic niche of a species, defined using only scenopoetic variables, contributes to shape its colonizable niche. Reductions of the abiotic niche, due to competition and dispersal restrictions, lead to the occupied niche (Soberón, 2007).

In this work, we explored the colonizable versus the occupied niche of S. villosa in one of its larger, undisturbed populations situated at the Feniglia dune system (Tuscany, Italy). Basing on a Strip Adaptive Cluster Sampling procedure and by applying unbiased Horwitz–Thompson estimators to the sampled data, we calculated the total abundances of both mature and juvenile thalli in the entire dune system. Then, we used the detailed plot-level dataset for testing two alternative hypotheses for the propagation of S. villosa. According to the first hypothesis, S. villosa is presently occupying most of its potential niche because many parts of the Juniperus shrubland are not a suitable habitat for this species. In this case, the environmental predictors would play a decisive role in shaping the abundance of both mature and juvenile thalli within the population. The second hypothesis predicts that the occupied niche of S. villosa is considerably smaller than its colonizable area because of the poor dispersal performance of the species. If the second hypothesis is correct, the effects of pure space and/or the abundance of mature thalli on the occurrence of juvenile thalli should overcome those of environmental factors, the juvenile thalli being in strict relation with the occurrence of mature thalli at the same site.

Section snippets

Methods

Seirophora villosa is a fruticose lichen with compressed-canaliculate laciniae, a hispid villose cinereous upper side, and a whitish, naked lower side. Apothecia are usually present, and are sub-apical, concave, and with red disks. In the Mediterranean basin this lichen is widespread, but not common, along the coasts of Spain, Portugal, Italy, the Greek islands, Israel and North Africa (Frödén and Lassen, 2004). In Italy, S. villosa has a western distribution along the peninsula (Nimis and

Results

By means of SACS, we detected four networks of sampling units occupied by S. villosa. Network extension and abundance were quite uneven, the latter ranging from only one sampled thallus to more than 3 000 (Table 1). Using Horvitz–Thompson estimators, we calculated that the overall population of S. villosa at the Feniglia dune system comprised more than 47 000 thalli. Nearly 90 % of individuals were juvenile, with only about 6 000 mature apothecia-producing thalli recorded. The entire population

Discussion

The S. villosa population was abundant at Feniglia, and included a considerable number of juvenile thalli, suggesting high spore production and good population fitness. On the other hand, mature thalli producing sexual spores were relatively rare, and were scattered throughout the Juniperus shrubland and clustered into very small sub-populations.

The small, non-significant effect of environmental distance on S. villosa abundance leads us to reject our first hypothesis that the species is

Acknowledgment

This research was carried out under the project COREM (Cooperazione delle Reti Ecologiche nel Mediterraneo) of the Operational Programme Italy – Maritime France 2007–2013, financed by European Regional Development Fund (ERDF).

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