SECCIÓN ESPECIAL
IMPACTO DE ACTIVIDADES PRODUCTIVAS SOBRE MAMÍFEROS DE ARGENTINA

Native mammals across grazing and restored woodlands: an overview of ecological connectivity in the central Monte Desert

Solana Tabeni¹, Florencia Spirito², and M. Florencia Miguel¹

¹ Instituto Argentino de Investigaciones de las Zonas Aridas, CCT CONICET MENDOZA. Mendoza, Argentina. [Correspondence: Solana Tabeni <stabeni@mendoza-conicet.gob.ar>].
² Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA) – CONICET, Facultad de Agronomía, Universidad de Buenos Aires. Argentina.

Recibido 20 julio 2016.
Aceptado 24 abril 2017.
Editor invitado: J. Priotto.
Editor asociado: M. Kittlein

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ABSTRACT.

The semi-arid regions of Argentina have been subject to numerous human activities such as grazing by domestic animals. These activities bring about changes in the spatial pattern of the landscape by altering a variety of ecological processes due to loss of natural habitats and reduction of native species diversity. In the central Monte Desert, the establishment of protected areas has been implemented as a strategy for the recovery of native woodland communities. In addition, to ensure woodland perpetuity and the maintenance of ecological functions it is required to incorporate new approaches that include woodland connectivity with the surrounding landscape. The response of small and medium-sized mammals to boundaries highlights the need to consider the species-specific response in the selection of resources, the use of space and scales of observation fitted for the species. We focused on the socio-political boundaries between land uses to illustrate the changes in structural connectivity and their impact on functional connectivity through seed dispersal by mammals. Overall, understanding how differently managed lands are structurally and functionally connected may help us to design better management strategies aimed at biodiversity conservation, with focus both on species and the ecological processes they are involved in.

RESUMEN.

Mamíferos nativos a través de bosques restaurados y pastoreados: una perspectiva de la co-nectividad ecológica en el desierto del Monte central.

Las tierras secas de Argentina han sido objeto de nu-merosas actividades humanas como el pastoreo por herbívoros domésticos. Estas actividades provocan cambios en los patrones espaciales del paisaje alterando una variedad de procesos ecológicos debido a la pérdida de los hábitats naturales y a la reducción de la diversidad de especies nativas. El establecimiento de áreas protegidas en el desierto del Monte central constituye una estrategia para la recuperación de las comunidades de bosques nativos. Adicionalmente, asegurar la perpetuidad del bosque, de sus funciones y procesos, requiere incorporar nuevos enfoques que contemplen acciones tendientes a incrementar la conectividad con el paisaje circundante. La respuesta de mamíferos pequeños y medianos a los bordes pone de relieve la necesidad de considerar sus requerimientos específicos en la selección de los recursos, el uso del espacio, así como también el uso de esca-las de observación ajustadas a las mismas. Nos centramos en los límites sociopolíticos entre usos de la tierra para ilustrar los cambios en la conectividad estructural y su impacto en la conectividad funcional a través de la dispersión de semillas por mamíferos. En general, la comprensión de cómo las áreas bajo diferente manejo están conectadas puede ayudarnos a diseñar mejores estrategias de manejo orientadas a la conservación de la biodiversidad.

Key words: Boundaries; Prosopis flexuosa; Protected areas; Rodents; Seed dispersal.

Palabras clave: Áreas protegidas; Bordes; Dispersión de semillas; Prosopis flexuosa; Roedores.

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INTRODUCTION

Grazing by domestic herbivores is considered one of the land uses that most contribute to global degradation of drylands (Peters et al. 2015). Particularly, dry woodland ecosystems are subject to incessant biomass extraction processes linked not only to grazing but also to deforestation (Grau & Aide 2008; Guevara et al. 2009; Vilela et al. 2009). The native woodlands of Prosopis flexuosa in the desert plains of central-western Argentina (Monte Desert) underwent the greatest deforestation during the first decades of the twentieth cen­tury, mainly associated to the expansion of the railway (Villagra et al. 2009). Intensive logging was intended for firewood, charcoal and gas production for urban lighting (Roig 1971). The gradual decline in forest products and the changes in ecosystem structure, mediated by the emergence of heliophilous species, favored the beginning of a new scenario characterized by expansion of livestock production systems. These practices affect multiple biotic and abiotic interactions mainly through loss of habitat, increasing landscape fragmentation, changing plant cover and biodiversity, and the provision of ecosystems services (Alvarez et al. 2006; Rojas et al. 2009).

In the context of land degradation, the estab­lishing of natural reserves has been an effective tool for the maintenance and conservation of woodland resources (Hobbs & Cramer 2008). Conservation efforts in the central region of the Monte Desert have increased the number of protected areas and experimental stations (as Ñacuñán Reserve and Telteca Reserve), promoting the passive recovery of the native communities. Furthermore, the exclusion of livestock activities demarcated the so-called socio-political boundaries as barriers defined by legal, institutional, and social processes (Dallimer & Strange 2015).

As in many dryland landscapes, the limits to the protection areas have not been designed to encompass the flows of water, energy, nutrients, and organisms across the landscape (Defries et al. 2007). On the contrary, protected areas are usually embedded in a matrix of land uses where expansion and intensification of human activities exert new visible pressures at the level of their boundaries. Moreover, the consequences of such fragmentation on preservation of species, ecosystem functions and provision of goods and services demanded by local communities are scarcely explored (Hansen & Defries 2007).

Global initiatives guided by the Strategic Plan for Biodiversity 2011-2020 (see www.cbd.int) and the UNCCD (United Nations Convention to Combat Desertification, see www.unccd.int) identified that one of the biggest chal­lenges ahead for biodiversity conservation is to enhance habitat connectivity, enabling the movement of organisms and resources. Desert mammals have been widely recognized to be mobile link species, with significant effect on ecosystem processes across the landscape. From local to regional scale, they have a role in the distribution of soil nutrients and seed dispersal (Lindenmayer et al. 2008; Giannoni et al. 2013), also having a scarcely explored role in the pol­lination of desert plants and dissemination of mycorrhizal fungi essential for the survival of many higher plants (Wilcox & Murphy 1985; Zoeller et al. 2016).

Overall several questions of growing interest arise: How the conservation practices and land uses can affect landscape connectivity for mam­mals? How the ecological functions performed by these organisms are influenced by changes in land use? In this paper we offer a synthesis based on regional studies to illustrate the ef­fect of grazing on mammals and conservation measures on native woodland. We will focus on how changes in landscape structure influence resources selection and movement of mammals. We will consider studies carried out in the Ñacuñán region in the Monte Desert, where the impact on native communities has been widely studied. Finally we will point out how changes in structural connectivity impact on functional connectivity through seed dispersal mediated by mammals.

PASSIVE RESTORATION AND CONSERVATION OF MAMMAL ASSEMBLAGES IN NATIVE WOODLANDS

Since the pioneering initiatives began, in the 60’s, aimed at the preservation of native wood­land and wildlife in the Monte Desert, the concept of protected area has evolved. Initial efforts setted the focus in restoring the natural conditions prior to disturbances, thus rigidly delimitating protected landscapes in isolation from their adjacent social-ecological context, often considered hostile. This deterministic perspective, based on the Clementsian suc­cessional paradigm (Briske et al. 2003) guided the design of protected areas around the world (Suding et al. 2004) as well as in the Monte woodlands. But the resources over-exploitation in the surrounding of protected areas, prin­cipally by agricultural land uses, resulted in isolation and lack of connectivity among pro­tected areas due to landscape fragmentation (Palomo et al. 2014). The emerging criteria for conservation in the 70’s focused on the inter-relationships between natural ecosystems and socio-economic processes (such as UNESCO’s Man and the Biosphere Programme). These ef­forts were focused on the integration of local communities, through the creation of buffer zones, and on the conservation strategy sup­ported by outstanding environmental values (Rubio et al. 2014).

Passive ecosystem restoration for the manage­ment of wildlife, after eliminating a stressor, such as livestock, seems to be a common approach for restoring degraded lands. While degraded land restoration depends on distur­bance history and intrinsic ecological potential of lands. The unassisted regeneration of eco­systems is considered to be the most efficient way in terms of cost-effectiveness to recover many components of their original biodiversity (Chazdon 2008; Hobbs & Cramer 2008).

The removal of livestock and subsequent development of plant biomass trigger a re­sponse that is inherently linked to disturbance intensity, site-specific properties, and time of cessation of disturbance. As a general pattern, it has been noted, within the first 10-20 years of grazing abandonment, the physiognomy of the fields is characterized by a phase of lower cover of therophyte plants and little recovery of the perennial grass layer. At least 20 years are required to observe a significant increase in the cover of perennial grasses, and 20-30 years to reach a state characterized by domi­nance of shrubs. After 30-40 years, long-term exclusion results in increased plant biomass, in turn leads to a significant spatial rearrangement of plant patches and modifications of certain functions, such as soil stability and nutrient cycling (Ruecker et al. 1998; Valone & Sauter 2005; Cramer et al. 2008; Arnaez et al. 2010).

The increasing appraisal of these areas with long-term exclusion grazing stock rests on the possibility of exploring the regeneration of ecological systems by autogenic processes. Specifically in the central Monte, after 50 years of grazing exclusion, natural habitats showed an increase in species diversity and richness compared to a previous state in which graz­ing was permitted (Rossi 2004). For instance, the abundance-dominance or frequency of the main palatable grasses such as Digitaria californica, Trichloris crinita, Pappophorum caespitosum, as well as some species of shrubs (Lycium tenuispinosum, Capparis atamisquea and Condalia microphylla) have increased con­siderably since then (Rossi 2004). Moreover, the increased of plant cover over time also restored the spatial arrangement of vegetation patches and consequently reestablished landscape con­nectivity (Tabeni et al. 2016). It seems that these changes in vegetation patterns induced spatial homogenization. Inside the protected areas, the strong contrast among pre-exclusion habitats tended to diminish, mainly due to colonization, distribution and expansion of some species through time (Roig 1971; Tabeni & Ojeda 2005).

By contrast, under the dominant production system, peripheral areas are mainly subjected to continuous grazing, by cows or goats, and to a lesser extent to rest-rotational grazing sys­tems (Guevara et al. 2009). These areas showed several signs of degradation, such as a total plant cover and grass strata reduction, and an increase in unpalatable species and bare ground cover (Villagra et al. 2009). Irrespective of these widely reported landscape indicators, habitat structure is important to the occurrence and persistence of native mammals. The continuous livestock grazing produced a landscape pattern with a high number of gaps in plant distribution and higher spatial heterogeneity (Spirito 2015; Fig. 1). This heterogeneity is also observed at a regional scale, showing variable spatial pat­terns of grazing management hotspots (e.g., ranch settlements, water sources) and a regional mosaic of highly aggregated vegetation clusters (Asner et al. 2003).

Fig. 1. Nonmetric multidimensional scaling ordination showing differences in habitat variables: grass, shrub, litter, tree, forb and bare ground; and structural variables: mean patch size of shrub (shrub-MPS), grass (grass-MPS), litter (litter-MPS), tree (tree-MPS) and mean inter-patch size of bare ground (bare ground-MiPS) in the passive restoration and grazed areas of the central Monte Desert (from Spirito 2015).

Specific responses of species according to their ecological requirements suggest that protected and peripheral areas can play dif­ferent and supplementary roles. Some studies have found in peripheral areas a decrease in species richness, diminished abundance and diversity of small and medium-sized mammals in response to reduction of the herbaceous-grass layers, increased bare ground and simplification of habitat structure (Wada et al. 1995; Keesing 1998; Eccar et al. 2000; Mathis et al. 2006). Thus, animals requiring densely vegetated patches, such as the gray leaf-eared mouse (Graomys griseoflavus), the grass mouse (Akodon dolores) or the yellow-toothed cavy (Galea leucoblephara), thrive in recovered habitats.

Otherwise, species with biological and mor­phological attributes to detect predators and exploit open habitats, such as Eligmodontia typus and Dolichotis patagonum, are more fre­quent in the surrounding grazed areas (Kufner & Chambouleyron 1991; Tabeni et al. 2013). For example, the woody clusters of P. flexuosa that occur in higher densities around settle­ments outside of the Ñacuñán Reserve (Asner et al. 2003), are food and shelter providers for cattle and native mammals like Microcavia australis. Considering that M. australis is an effective seed dispersal agent for P. flexuosa, it could play a key role for the native woodland regeneration under anthropogenic disturbance (Campos et al. 2017; Miguel et al. 2017). The spatial proximity of these seed sources to pro­tected areas highlights many still unexplored aspects, such as seed dispersal across bound­aries by native mammals, spillover processes across fences and improvement of functional connectivity between management conditions (Gray et al. 2016).

It is well known that resource selection de­pends on the spatial scales at which organisms perceive changes in the landscape (Wiens 2002). From small to coarse scale, small mammals inside and outside of protected areas, follow a non-random distribution, forming clumps associated with habitat patches and plant cover types (Tabeni et al. 2007). Spatially explicit analyses point out how even species that avoid grazed lands around protected areas, can find suitable habitats within the available patches. For example, inside of grazing areas, A. dolores was more abundant in ungrazed vegetation patches where the high density of grasses, act­ing as a refuge, could reduce its vulnerability to predation (Tabeni et al. 2007).

The role of these refuge patches, proved to be of importance for the conservation of des­ert mammals (Pavey et al. 2015). Therefore, land management can play a crucial role in sustaining animal populations in a disturbed matrix through the provision of refuges, food composition and distribution of diverse types of covers (Shenbrot et al. 1999).

SMALL MAMMALS RESPONSE TO BOUNDARIES

Boundaries between protected areas and their surrounding grazing lands are usually physical barriers, such as fences, which may influence the movement of wildlife across these areas (Durant et al. 2015). This infrastructure is in itself seen as a disturbance for wildlife given its effect in habitat fragmentation. In other words, it provides perches for raptor species, thereby increasing the risk of predation, and especially it acts as a barrier to the movement and dispersal of animals (Wisdom et al. 2013).

This boundary conforms one of the first filters for organism dispersal across a fragmented landscape, thus affecting many processes and functions performed by mobile organ­isms (Cousins 2013). Boundary permeability depends on both its physical features and each species’ perception of habitat features (Cadenasso et al. 2003). Usually, socio-political boundaries are considered to be an effective barrier to inhibit the movement of livestock and native wildlife of a considerable size (Wisdom et al. 2013). These boundaries represent a change between two habitat conditions, therefore it raises the question on whether they can con­stitute an obstacle to the movement of small mammals in the Monte Desert. Previous studies in agricultural matrices revealed that boundary habitats are less disturbed than adjacent patches of agricultural fields. Consequently, they main­tain high plant cover throughout the year and provide good habitat conditions for mobile organisms such as small rodent species (Hodara & Busch 2006; Bilenca et al. 2007; Sommaro et al. 2010). However, habitat conditions across boundaries and their consequences on mobile organisms in drylands, under extensive cattle grazing, have been almost unexplored (see Wilson et al. 2010). The distinction between ecological boundaries (i.e., the natural boundar­ies between habitats and ecosystems) of those imposed by ecosystem management, has al­lowed us to observe that the habitat structure of socio-political boundaries impacted on the abundance of small mammals (Fig. 2). These boundaries were more contrasting in habitat variables than the ecological ones and a strong contrast was perceived by small mammals as quality changes across managements units, leading to lower richness in the mammal as­semblage (Spirito & Tabeni 2016).

Fig. 2. Total abundance of small mammal spe­cies along ecological and socio-political boundar­ies. Ecological boundar­ies are Larrea shrubland – Prosopis woodland under continuous graz­ing conditions and under passive restoration. The socio-political boundary in Prosopis woodland between continuous grazing and passive res­toration (from Spirito & Tabeni 2016).

RESOURCE SELECTION AND MOVEMENT PATTERN UNDER MANAGEMENT CONDITIONS: FUNCTIONAL CONNECTIVITY FOCUS ON G. griseoflavus

Connectivity is an important component of dryland ecosystem given its relation to the flow of soil resources and seeds across the landscape (primarily by wind and water, but also by animals; Okin et al. 2015). If we focus on a mobile organism, many factors intrinsic to the species influence decisions to leave a habitat patch and move to another, namely anti-predatory behavior, acquisition of resources, competition and social interactions, among others (Nams 2005; Fahrig 2007). Changes in the movement of animal also induce modifica­tions in their home-range sizes (Spencer 2012). Many space-use models assume home-range existence a priori rather than treating it as an emergent property of animal movements (Pow­ell & Mitchell 2012). Knowledge of how landscape features affect the movement of organisms and home-range size, is critical for address­ing the impacts of degradation (Fisch­er & Lindenmayer 2007) and poten­tial landscape-level conservation initiatives (Minor & Lookingbill 2010).

Spirito (2015) studied functional con­nectivity in the central Monte Desert using G. griseoflavus, the most abundant small mam­mal in the Ñacuñán region, as an example of a mobile organism, and analyzed its response to grazing-induced changes in landscape structure. When analyzing landscape structure, Spirito (2015) found a clear differentiation in vegeta­tion communities in the Ñacuñán Reserve. Spe­cifically, there was greater connectivity among plant patches and higher litter and forage cover (i.e., species consumed by G. griseoflavus) than the area under grazing. The most structurally connected sites were associated with increased movement and space used by this species. Movement patterns, studied through the step-length and home-range size, denoted a lower movement in grazed areas (step-length 9.91 ± 3.17 m; home-range 992.45 m²), than in areas under passive restoration (step-length 25.43 ± 3.71 m; home-range 3099.69 m²).

Most resource selection studies show that small mammals select resources to take refuge from predators and ensure food access by avoid­ing open spaces (Turcotte & Desrochers 2003; Corbalán et al. 2006). As a main outcome, G. griseoflavus seems to display a different strategy depending on the management used. Under passive restoration, this species selected grass patches, while outside of the restoration area it chose patches with high species richness avoiding the open space (Fig. 3). This highlights how fine-scale changes in the landscape are perceived by small mammals pointing to them as significant constraints on their movement and ecological requirements (Spirito 2015).

Fig. 3. Environmental variables estimates from Resource selec­tion functions (RSF) models for G. griseoflavus in the Monte Des­ert of central Argentina. Stan­dardized parameter estimates (Std βi) are reported so that the effect size of model variables can be compared. Std βi denoted the selection (positive values) or avoidance (negative values) for environmental variables under the two management conditions (grazed vs passive restoration). The models were divided into (a) habitat variables (forage rep­resents the species consumed by G. griseoflavus) and (b) structural variables (MiPS = mean inter-patch size; forage-MPS = mean patch size of forage species and roadDist = distance to roads).

A FUNCTIONAL INTERACTION ACROSS SOCIO-POLITICAL BOUNDARIES: Prosopis flexuosa FRUIT REMOVAL BY TERRESTRIAL MAMMALS

In socio-political boundaries, some ecological functions can be affected, with consequences for biodiversity (Cadenasso & Pickett 2001; Cadenasso et al. 2003). The activity of animals along boundaries can be affected by their re­sponses to these habitats, and therefore some ecological processes, such as seed dispersal, may be modified (Chauvet & Forget 2005).

Seed dispersal is one of the most important ecological functions in the life cycle of plants (Nathan et al. 2009). Considering the increased use of lands by humans, the number of studies evaluating the effects of anthropogenic activi­ties on seed dispersal has increased over the last years. Specifically, they have assessed the effects of habitat fragmentation (Markl et al. 2012; Aliyu et al. 2014), defaunation (Galetti & Dirzo 2013; Dirzo et al. 2014; Galetti et al. 2015) and selective logging (Ochoa 2000; Forget & Cuijpers 2008; Markl et al. 2012). Previous studies have found a higher probability of a seed being predated than dispersed in frag­mented habitats, mainly due to a higher seed availability on less disturbed sites (i.e., high seed abundance may satiate seed-predating rodents; Forget et al. 2002; Aliyu et al. 2014). Furthermore, an increase in seed predation by small mammals on defaunated sites, explained by direct and indirect impacts of large herbi­vores on small mammal communities has been reported (Galetti et al. 2015).

In the Monte Desert, fruits of P. flexuosa are consumed by a variety of native and domestic mammals. Some species disperse Prosopis seeds by endozoochory (Bos taurus, D. patagonum, Lycalopex griseus; Campos et al. 2008; Cam­pos & Velez 2015), others by hoarding the seeds in small caches on the ground (scatter-hoarders, E. typus, M. australis; Giannoni et al. 2013; Campos et al. 2017), and small rodents mainly prey upon Prosopis seeds (A. dolores, G. griseoflavus; Giannoni et al. 2013). Considering seed dispersal is a crucial ecologi­cal function for woodland recruitment, seed removal by different animal species may involve different seed fates and consequently affect plant population dynamics (Jordano & Herrera 1995). Therefore, it is essential to understand how seed removal can be affected by changes in the habitat due to different types of land management. Yet this aspect remains poorly explored in the Monte. However, recent stud­ies have evaluated the effect of different land uses on Prosopis dispersal, with focus on the removal of its propagules by animals. In this sense, fenced and unfenced reserves varied in the main animal seed removers. Thus, in fenced reserves the main Prosopis seed removers were medium and large-sized mammals, while in the fenced ones were small- sized rodents (Campos et al. 2017). Because mutualistic interactions may be altered by anthropogenic activities (Dirzo et al. 2014), the effect of grazing on Prosopis seed dispersal showed seed predators removed a high number of seeds at an ungrazed site while animals that mainly disperse seeds removed a high number of Prosopis seeds at site under grazing (Miguel et al. 2017). These results suggest that animal species from the Prosopis frugivore assemblage remove seeds at different intensities according to the land use.

Future studies on ecological interactions in boundaries between different land uses may contribute to a better comprehension of the functional connectivity between land manage­ments. Animals with different functional roles in the seed dispersal process may respond differently to socio-political boundaries, with different implications for seed survival and native tree recruitment.

DISCUSSION AND CONCLUSIONS

The demarcation of protected areas and the exclusion of persistent disturbance, such as grazing by domestic herbivores, are neces­sary but not sufficient strategies to ensure the conservation of biodiversity (Hobbs & Cramer 2008). The growing land use demands in the peripheries, and how these affect the native wildlife, highlight the extent to which manage­ment areas influence each other beyond the physical or legal barriers imposed.

We note that, over time, disturbance exclu­sion and increasing improvement in the Monte woodlands have molded a singular form of connectivity between mammals and their surroundings, whose fu­ture consequences are still unknown.The long-term passive restoration pro­moted the expansion of shrubland and woodland patches and the increase in plant density, favoring rodent species requiring densely vegetated patches (e.g., G. griseoflavus, A. dolores or G. leuco­blephara). On the other hand, the extensive livestock grazing resulted in more contrasting landscape with a high number of open spaces interspersed with vegetation patches that allow the occupation of a greater diversity of spe­cies, from small to medium-sized mammals, as some endangered species, such as the en­demic Patagonian hares (D. patagonum). This contrasting heterogeneity plays a major role in understanding species responses to landscape changes caused by grazing impact. We stress the importance of assessing the response of mammal species considering spatial scales fit­ted for the species under study. At fine scale, the spatially explicit analysis showed that both grazing impact and the long processes of veg­etation recovery imply high intra-habitat vari­ability in the spatial organization of resources for mammals such as the cover of trees, shrubs and grasses. These signals in the habitat are perceived by the animals, impacting not only in their abundances, but also in their spatial dis­tributions while searching for optimal patches.

As mammal assemblages change in conso­nance with the varying landscape it is necessary to incorporate a functional approach. Thus interpreting connectivity as a species-based attribute, the landscape will have many pos­sible forms of connectivity based on the habitat requirements and dispersal capacity of each species (Watts & Handley 2010). The movement of animals between socio-political boundaries and their decision to move between patches are influenced by many features of boundaries and the intrinsic characteristics of the species (Fahrig 2007). In studies of movement and home-range size of a native small mammal in the Monte (G. griseoflavus) we found that its step length and home range were larger on a site subject to passive restoration than in grazed areas (Spirito 2015). Therefore, to highlight how landscape features affect the movement of or­ganisms and the home-range size can be critical for addressing the impacts of degradation and future landscape-level conservation initiatives.

The most current approaches have begun to inquire whether mammal species play an es­sential role as promoters of the restoration of degraded ecosystems by connecting different or similar habitat patches through the distri­bution of resources (Martin 2003; Yoshihara et al. 2009). Even more important is that key processes, such as nutrient distribution and seed dispersal, can be affected when faunal assemblages of degraded sites loose mammal species performing these functions (Chillo & Ojeda 2012; Dirzo et al. 2014). To study the occurrence of mammals across boundaries, and their different roles in the seed dispersal process are ways to know how restored and connected different managed units are. In our study area, the different functional activities of mammals along boundaries (i.e. seed predators, endo­zoochorous dispersers and scatter-hoarders) may imply different probabilities for a seed to be predated or dispersed and therefore constitute indicators of processes under threat, essential for woodland recruitment.

In light of the rapid changes taking place in land use and socio-economic dynamics it may be predicted that many protected areas around the world will be under the influence of increasing pressures (Defries et al. 2007). The dry woodland of central Argentina is not out of this scenario; on the contrary, the region is also expected to face strong processes of re­structuring production and changes in land use with environmental and social consequences (Torres et al. 2014) that will expose wildlife to new vulnerabilities.

Overall, the implementation of reserves is a very useful strategy to conserve biodiversity, but we should consider the connectivity of the entire landscape. Protected areas should be structurally and functionally connected with their surroundings, allowing that species find their requirements in several habitat patches (Soulé & Terborgh 1999; Fuller et al. 2006). Decision making for conservation, facing in­creasing degradation, must be prioritized, under a framework that considers the structural and functional diversity of the landscape, and the preservation of key elements for the viability of mammal populations, such as connectivity between habitats.

ACKNOWLEDGMENTS

We are grateful to F. Yannelli, N. Horak and the reviewers for their helpful comments and suggestions on improving this manuscript. We thank to Agencia Nacional de Pro­moción Científica y Tecnológica and CONICET for their financial support (PICT 0185, PIP 2012-2014/112 201101 00601 and PIP 2013-2015/112 201201 00270). We thank to J. Priotto for organizing the Symposium “Impacto de actividades productivas sobre la diversidad, distribución y abundancia de mamíferos de Argentina: consecuencias funcionales y perspectivas para su conservación”, held in the XXVIII JAM Santa Fe (November 2015).

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GLOSSARY

Passive restoration: ecological systems are likely to recover unaided through ecological succession rather than through active restoration strategies (Armesto et al. 2007).

Boundary permeability: the probability of crossing a boundary between two landscape components (Wiens 2002).

Structural connectivity: defined by the spatial structure and composition of the landscape, independent of any attributes of the organism(s) of interest (Rudnick et al. 2012).

Functional connectivity: relative to the requirements of the organisms that live landscape and move through the landscape structure, and describes the extent to which landscape fragments facilitate or prevent the movement of an individual among resource patches (Tischendorf & Fahrig 2000; FitzGibbon et al. 2007).

Step-length: straight line connecting two successive locations of the same individual at regular time intervals (Turchin 1998).