An experimental study of the effects of weed invasion on lizard phenotypes

Abstract

We examined how a weed affected the basking and activity of a diurnal lizard, and the potential cascading effects of these shifts for life history strategies and expression of morphology. Hatchlings of the diurnal lizard Lampropholis delicata were raised to maturity in outdoor enclosures that mimicked high, moderate and low invasion by a sprawling plant (blue periwinkle, Vinca major). Skinks depend on sunlight for growth and maintenance. Periwinkle differs from displaced grassland by being structurally complex and blocking sunlight. Lizards restricted to the enclosure floor achieved preferred body temperatures only when exposure to periwinkle was moderate or low. However, lizards in high invasion enclosures could reach preferred body temperatures by climbing plants and basking on exposed canopy. This shift in basking strategy resulted in lizards growing longer hind limbs compared with animals that rarely (moderate invasion) and never (low invasion) climbed plants. Consequently, lizards reared in high invasion enclosures sprinted faster than conspecifics reared in lower invasion environments. Throughout the study there was no significant variation among treatments in the tendency of animals to be moving when they were not hidden. However, lizards in high invasion treatments hid more often during the day, were lighter in body mass, and females had lighter clutch masses and offspring than did those from moderate and low invasion enclosures. Thus, microhabitat degradation can drive a cascade of changes to an animal's ecology.

Absence of Climbing-Induced Limb Length Plasticity in the Eastern Fence Lizard,Sceloporus undulatus

“…Although it is possible that the climbing behavior induced by our manipulations was not sufficient, limb length plasticity has been documented as a result of less frequent climbing activity than we elicited in our study. Lampropholis delicata skinks that were observed climbing invasive plants to bask in only 45% of behavioral observations (compared to 63% in our study, using the same observation protocol) exhibited an associated increase in RHL (Downes and Hoefer, 2007). Additionally, our measure of the number of times lizards climbed on or off the platform is likely an underestimate because transitions in which the lizard returned to its original location before the next observation period, an hour later, would not have been recorded.…”

“…For example, longer limb length can be triggered by increased climbing activity following weed invasion (Garden Skinks, Lampropholis delicata, Downes and Hoefer, 2007) or by perching on broader branches to escape introduced predators (e.g., Brown Anole, Anolis sagrei, Losos et al, 2000). Understanding whether relative limb length can change plastically is important for illuminating the drivers of this ecologically important trait and for predicting how populations will respond to environmental perturbations.…”

Mechanisms of the impact of a weed (grader grass, Themeda quadrivalvis ) on reptile assemblage structure in a tropical savannah

“…In our study, temperatures within grass clumps were very similar among habitats, which contrasts with the findings of some other studies reporting cooler temperatures in weeds (Valentine, 2006) or less opportunities for thermoregulation in weeds (Downes and Hoefer, 2007;Hacking et al, 2014). We recorded temperatures only within grass clumps, and not in a range of habitat types at each site.…”

“…The influence of weeds on reptile assemblage composition and abundance may be driven by a variety of factors. Food availability may be altered in weeds (Valentine, 2006;Martin and Murray, 2011), predators may be more abundant or more successful in weeds (e.g., Thompson, 1987), habitat structure of weeds may alter behaviour, such as movement and social interactions (Newbold, 2005;Downes and Hoefer, 2007;Rieder et al, 2010;Steidl et al, 2013), or influence thermoregulation (Valentine, 2006;Downes and Hoefer, 2007). Studies examining the likely sources of the impacts of weeds are required to predict the effects of weeds in different habitats and on other faunal assemblages (Martin and Murray, 2011).…”

Invasive fire ants alter behavior and morphology of native lizards

“…They are occupied by temperate mixed forest; however both lizards and fire ants are primarily found in open disturbed areas, or along forest edges (Stiles andJones 1998, Trauth et al 2004). Smaller-scale measurements of habitat variables that are known to be important in influencing lizard habitat use and morphology (canopy openness, perch-site diameter, and ground cover composition, Langkilde et al 2003, Kolbe and Losos 2005, Downes and Hoefer 2007 showed no overall difference between sites (Appendix D). The habitat variables that do differ among sites (Site 4 has less vegetation cover than Site 2) do not follow a trend with time since invasion.…”