Mass-related differences in metabolic rate and fasting endurance explain divergence in seasonal activity of Mediterranean lizards

Abstract

We analysed the effects of body mass on the monthly activity patterns of six Mediterranean lacertid lizard taxa, four relatively small species, the Italian wall lizard (Podarcis siculus), the common wall lizard (Podarcis muralis), the blue-throated keeled lizard (Algyroides nigropunctatus), and the Ionian wall lizard (Podarcis ionicus), and two larger species, the western green lizard (Lacerta bilineata) and the Balkan green lizard (Lacerta trilineata). The highest number of observations for all six species occurred in April and May and the lowest in July and August, the latter being the hottest and driest months of the year. The two larger species were mainly active from March to July, whereas the four smaller species had an additional period of high activity from September to November. As all six species reproduce during spring, the increase in activity of the smaller species in autumn was consequently unrelated to reproductive behaviour. There was no difference in seasonal activity of the two smaller Italian species at sites with or without the larger green lizards. It is therefore unlikely that interference competition/predation by green lizards caused the increased autumnal activity of the smaller lizards. We suggest that due to their lower mass-specific metabolic rates, larger species can obtain sufficient lipid stores over a shorter annual activity to ensure successful reproduction the subsequent spring. By contrast, smaller species have greater need to replenish their lipid reserves after summer fasting and therefore resume much higher activity levels in September to November to attain this goal.

Application of Univariate Diversity Metrics to the Study of the Population Ecology of the Lizard Lacerta bilineata in an Ecotonal Habitat

“…The midsummer gap found in the recent study of Mediterranean lacertid lizards was confirmed here (Question 4) and was also in agreement with the reproductive period in more southerly areas, such as Greece and Italy, which is from March to July [29]. The midsummer gap that followed the reproductive period was observed annually during the 4-year study and did not exhibit any particular sex bias.…”

“…A single annual reproductive period in L. bilineata with a later spring emergence and fewer autumn sightings, along with earlier entry into winter dens, must reduce the predation risk in lacertids [39] and is likely to be an adaptive trait. The similar but less definite midsummer gap recorded in the sympatric Podarcis muralis in the same hedgerow [36] also supports a previous study [29], where sightings of small lacertids in comparison with larger species were greater during the midsummer gap. This was attributed to the differences in the capacity of larger lacertids for fasting endurance, which is estimated to be up to 1.65 times greater than that of smaller lacertids [29].…”

“…The similar but less definite midsummer gap recorded in the sympatric Podarcis muralis in the same hedgerow [36] also supports a previous study [29], where sightings of small lacertids in comparison with larger species were greater during the midsummer gap. This was attributed to the differences in the capacity of larger lacertids for fasting endurance, which is estimated to be up to 1.65 times greater than that of smaller lacertids [29]. The double reproductive period in P. muralis may explain the shorter gap in this species and hence the need for a longer active season to replenish energy stores previous to the winter dormancy period.…”

“…( 4) What is the annual activity period and is there a midsummer gap, as found in other lacertids? This question originates from a study by [29], where several species of lacertid, including L. bilineata, showed what could be described as a midsummer gap.…”