1. In Mediterranean ant communities, a close relationship has been found between activity rhythm in the period of maximum activity and position in the dominance hierarchy: subordinate species are active during the day, when conditions are more severe, while dominants are active during the afternoon and the night.

2. Results obtained in this study confirmed that the species foraging at higher temperatures were closer to their critical thermal limits than the species foraging at lower temperatures.

3. This enabled two extreme strategies of foraging in relation to temperature to be distinguished: (1) heat-intolerant ant species behaved as risk-averse species, foraging at temperatures very far from their critical thermal limits; and (2) heat-tolerant ant species behaved as risk-prone species, foraging very near their critical thermal limits and running a high heat mortality risk.

4. Heat-tolerant species benefited from this strategy by having better foraging performance at high temperatures.

5. This wide range of thermal niches may be one reason why Mediterranean ant faunas are so diverse in the face of limited diversity in vegetation and habitat structure: the daily range of temperature may be sufficiently great to meet the requirement both of heat-adapted and cold-adapted species as well as a spectrum of intermediate forms.

/pdf/critical-thermal-limits-in-mediterranean-ant-species-trade-55nh2akmr1.pdf

Critical thermal limits in Mediterranean ant species: trade‐off between mortality risk and foraging performance

The goals of this article are to present as complete and broad an update of tiger beetle biology as possible, and to introduce tiger beetles to biologists seeking an ideal group of organisms for testing and integrating generalizations in such areas as ecology, physiology, behavior, morphology, phylogeny, and biogeography. Because of their distinct color patterns, their occurrence in habitats where they are readily observed, and the extremely rapid running and flight of the adult forms, which make them challenging to collect, tiger beetles have also been the focus of many amateur collectors. A natural alliance of amateurs and professionals resulted in a journal, Cicindela, which has been published quarterly since 1969. Among the general articles published on tiger beetles, five present a broad and readily understandable overview of tiger beetle biology (61, 63, 168, 175, 183). A preliminary list of papers dealing with tiger beetles of the world has also been published in two parts (85, 86).

Biology of Tiger Beetles

Behavioural regulation of body temperature in thermally heterogeneous habitats requires different amounts of time that could otherwise be dedicated to foraging and social activities. In this study I examined how four populations of the lizard Zootoca vivipara along an altitudinal gradient (250-1450 m) adjust their thermal-physiology traits and thermoregulatory behaviour to compensate for increasing time costs of thermoregulation. I focused on variation in several physiological (set-point temperature, heating rate) and behavioural traits (microhabitat selection, basking frequency, extent of thermoregulation). To estimate potential time spent basking and foraging by lizards that were not employing any behavioural compensatory mechanism, I used a simple biophysical model of thermoregulation, including information about operative temperatures at the study sites, selected temperature range, and heating/cooling rates. Time costs of thermoregulation for each population were calculated as potential time spent bas...

To heat or to save time? Thermoregulation in the lizard Zootoca vivipara (Squamata: Lacertidae) in different thermal environments along an altitudinal gradient

[Ontogenetic development in reptiles entails major changes in size-related foraging options. We studied the changes in foraging behavior of marine iguanas. In this species, size increases about twenty- to hundredfold from hatching to full adult size. The foraging strategy of marine iguanas was studied at Miedo on Santa Fe Island in the Galapagos archipelago. During low tide, large marine iguanas (>250 mm snout vent length (SVL)) foraged more in the lower intertidal than small ones ( 250 mm snout vent length (SVL)) foraged more in the lower intertidal than small ones (<250 mm SVL) which preferred the upper intertidal with higher temperatures and less frequent wave washing. Animals usually returned to the same foraging site day after day and had lower food intake after changing their foraging site. Feeding accounted for 60% of the time spent in the intertidal. Smaller animals fed every day, larger ones only every other day. Smaller individuals shuttled faster between foraging and basking sites than larger ones. Total feeding time per day was, however, the same for both size classes. At neap tides (= high water level at low tide) animals had shorter foraging bouts than at spring tides with much lower water levels at peak low tide. Length of feeding bouts depended most on wave action, time of low tide (during the daylight period), and body mass of an animal. Small animals fed significantly less at higher than at lower wave activities. All animals on Santa Fe spent more time feeding in the intertidal than in the subtidal. Only large males additionally foraged subtidally and the more so the bigger they were. During the reproductive season, territorial males were less likely to go foraging, but when feeding, territorials fed more subtidally than nonterritorials, went foraging earlier, and spent less time foraging in the IT than nonterritorials. Ability to resist wave drag increased with body size but did not decrease at lower body temperature, whereas running speed did so significantly. Bite frequency during foraging also decreased with decreasing body temperature and smaller, younger animals had higher bite rates than older, bigger ones. White-painted animals rewarmed slower than naturally black ones and partially compensated for this by shortening foraging bouts but increasing their number. The observed age-related changes in foraging behavior can be explained by postulating a rule of the form 'forage while warm and warm up when getting inefficient at grazing'. Of course, animals will also stop feeding should the stomach be filled before the end of the low tide cycle. To explain age- and motivation-related differences in foraging behavior, the only change that needs to be postulated is in the thresholds of body temperature inducing switches from foraging to warming-up and back. These changes are adaptive responses to size-related changes in costs and benefits of foraging in a cool, wavewashed environment.]

H. Dreisig

Papers

A time budget model of thermoregulation in shuttling ectotherms