Detecting fragmentation extinction thresholds for forest understory plant species in peninsular Spain.

Marta Rueda,Ignacio Morales-Castilla,Mila Ferrero,Miguel Á Rodríguez,Fabio S Albuquerque,Juan Carlos Moreno Saiz

doi:10.1371/journal.pone.0126424

Marta Rueda, Ignacio Morales-Castilla + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0126424

Copy DOI

Abstract

Ecological theory predicts that fragmentation aggravates the effects of habitat loss, yet empirical results show mixed evidences, which fail to support the theory instead reinforcing the primary importance of habitat loss. Fragmentation hypotheses have received much attention due to their potential implications for biodiversity conservation, however, animal studies have traditionally been their main focus. Here we assess variation in species sensitivity to forest amount and fragmentation and evaluate if fragmentation is related to extinction thresholds in forest understory herbs and ferns. Our expectation was that forest herbs would be more sensitive to fragmentation than ferns due to their lower dispersal capabilities. Using forest cover percentage and the proportion of this percentage occurring in the largest patch within UTM cells of 10-km resolution covering Peninsular Spain, we partitioned the effects of forest amount versus fragmentation and applied logistic regression to model occurrences of 16 species. For nine models showing robustness according to a set of quality criteria we subsequently defined two empirical fragmentation scenarios, minimum and maximum, and quantified species’ sensitivity to forest contraction with no fragmentation, and to fragmentation under constant forest cover. We finally assessed how the extinction threshold of each species (the habitat amount below which it cannot persist) varies under no and maximum fragmentation. Consistent with their preference for forest habitats probability occurrences of all species decreased as forest cover contracted. On average, herbs did not show significant sensitivity to fragmentation whereas ferns were favored. In line with theory, fragmentation yielded higher extinction thresholds for two species. For the remaining species, fragmentation had either positive or non-significant effects. We interpret these differences as reflecting species-specific traits and conclude that although forest amount is of primary importance for the persistence of understory plants, to neglect the impact of fragmentation for some species can lead them to local extinction.

Highlights

Key issues concerning conservation related to the anthropogenic alteration of natural habitats include the amount of habitat needed to achieve conservation goals and the importance of habitat fragmentation [1]
For the scenario of increased fragmentation, only two species showed negative Oj, fragm values with 95% Confidence Intervals (CIs) not overlapping zero (Fig 2B). These species were significantly negatively affected by fragmentation and comprised one herb (M. hypopitys) and one fern (P. aculeatum), the latter had a weaker response as indicated by the close proximity of its upper 95% CI to zero
We suggest that variation in shade tolerance across species, and in their respective possibilities to survive in more open, fragmented habitats may likely result in a range of responses to fragmentation that preclude finding clearer patterns

Summary

Introduction

Key issues concerning conservation related to the anthropogenic alteration of natural habitats include the amount of habitat needed to achieve conservation goals and the importance of habitat fragmentation [1]. The term habitat fragmentation has often been used loosely to illustrate habitat destruction by humans even though habitat might be removed without increasing fragmentation [4]. This has generated a misunderstanding of the impacts of habitat amount and fragmentation on biodiversity [3]. The debate extends to distinguishing habitat loss per se from habitat fragmentation per se [2, 3], or to their interdependence, recognizing that fragmentation is usually a consequence of habitat loss [6]

Methods

Results

Conclusion