Habitat deterioration affects body condition of lizards: A behavioral approach with Iberolacerta cyreni lizards inhabiting ski resorts

Abstract

We analyzed whether habitat deterioration due to ski slopes affected lizards’ behavior, and whether these changes in behavior had consequences for the body condition and health state of lizards. Results suggested that habitat deterioration in ski slopes not only implied a loss of optimal habitat for lizards, but also led to an increase in perceived risk of predation. Males seemed to adjust their movement patterns to differences in risk, increasing their movement speed during their displacements across risky areas within ski slopes, but as a consequence, they incurred loss of body condition. A laboratory experiment supported that fleeing at high speeds in areas without refuges can be a factor responsible for reduced body condition. However, changes in body condition did not affect sprint speed of lizards. Our study provides new evidence that behavioral strategies to cope with increased predation risk, due to human-induced habitat deterioration, may affect body condition of lizards. Our results have applications for the design of conservation plans for this endangered lizard species. Environmental impact studies should be performed before opening new ski slopes, but taking into account not only the presence of lizards but also their body condition. An effective way to decrease the effects of habitat loss may be the artificial restoration of some refuges to create safe corridors for movement.

Introduction

One of the main strategies of prey to cope with predation risk is the selection of safe habitats where they can attend their requirements while minimizing predation risk (e.g., Lima, 1998, Amat and Masero, 2004). Habitat selection may decrease conspicuousness of prey, and provide refuges to hide from attacking predators (Arthur et al., 2004). However, natural vegetation appears nowadays deeply modified by human activities, and this change in habitat structure may increase perceived risk of predation (Whittingham and Evans, 2004). For example, deterioration of vegetation may make animals more conspicuous and thus, more vulnerable to predators (Martín and López, 1998), which will require animals to increase the frequency of costly antipredatory behaviors.

One of these antipredatory behaviors is the modification of activity and locomotor patterns (Martín and Salvador, 1997a, McAdam and Kramer, 1998), such as a decrease in activity to avoid the attack of predators that localize their prey by their movement (Hecnar and M’Closkey, 1998, Downes, 2001, Weber and Van Noordwijk, 2002, Laurila et al., 2004), or, when movement is required, a modification of locomotor patterns (Martín and Salvador, 1997a, McAdam and Kramer, 1998) to decrease time exposed to potential predators (López and Martín, 2002, Miles, 2004). Antipredatory behaviors such as fleeing at high speed and refuge use are costly. For example, Podarcis muralis and Psammodromus algirus lizards submitted to a high predation pressure suffered a loss of body mass (Martín and López, 1999a, Pérez-Tris et al., 2004). Therefore, an excessive allocation of time and energy to antipredatory strategies can decrease body condition, with important consequences for short and long term fitness. Furthermore, the loss of body condition could also decrease the ability to invest in defense against parasites (Cooper et al., 1985, Smallridge and Bull, 2000). However, there are no studies about the costs, in terms of body condition and health state, of changes in movement patterns in response to increased predation risk.

The Iberian rock lizard, Iberolacerta cyreni (=Lacerta monticola cyreni), is an endemic endangered small diurnal lacertid found mainly in rocky habitats in some high mountains of the Iberian Peninsula (Martín, 2005). However, this lizard suffers a loss of optimal habitat due to the construction of ski infrastructures (Martín and Salvador, 1997b, Pérez-Mellado, 2003). The natural vegetation of the ski slopes is badly affected (Martín and Salvador, 1997b), causing a considerable impact on the whole ecosystem (Haslett, 1991, Illich and Haslett, 1994, Wipf et al., 2005). The lack of vegetation and rocks causes a loss of cover and potential refuges for lizards (Martín and Salvador, 1997b), and thus, it creates areas with higher level of predation risk.

Here we analyzed whether male lizards have different microhabitat use and locomotor patterns in areas with two levels of perceived predation risk, induced by anthropogenic changes in microhabitat structure (i.e., construction of ski slopes), and whether these differences had consequences on their body condition and health state. We choose males because they defend territories by performing continuous movements across their home range searching for females and expelling intruder males (Martín and López, 2000, Aragón et al., 2001). Therefore, males may be more susceptible than females to predation because they have higher movement rates and are more conspicuous (Martín and Salvador, 1997a, Martín and López, 1999b, Martín and López, 2000). We therefore examined the effects of habitat deterioration on: (a) microhabitat selection, (b) spontaneous movement patterns, and (c) body condition, immune response, and parasite load of male lizards. We predicted that males should not use microhabitat at random, and therefore, regardless of possible differences in cover of shrubs and rocks between areas, we expected that lizards selected similar and safe microhabitats in both areas (i.e., those close to refuges such as shrubs or rocks). However, because males need to patrol their entire home ranges, we also predicted that males would incur higher predation risk while moving in ski slopes. Thus, we expected that, in ski slopes, males would increase speed when crossing unsafe areas far from refuges to reduce time exposed to predators. However, since moving at high speed is more costly than moving slower (Kramer and McLaughlin, 2001, Gleeson and Hancock, 2002), we expected that these males would suffer a loss of body condition, which might also affect their health state.

Many factors other than speed during displacements may affect body condition of males. Therefore, we performed a laboratory study to analyze the effect of fleeing at high speed on body condition and health state of lizards. We expected that lizards that were forced to run by a simulated predator and did not have a close refuge for hiding might suffer a loss of body mass after several attacks, whereas lizards that did not need to run for longer, because they have a close refuge, would not decrease their body mass. Immediately after this experiment, we measured sprint speed of lizards when they were forced to flee to test whether differences in body condition affected escape speed. We did not expect differences in escape speed of lizards of similar body size regardless of their body condition.