Giacomo Santini

Competition trade‐offs in the organisation of a Mediterranean ant assemblage

Abstract 1. The organisation of an ant assemblage inhabiting an olive orchard in central Italy was analysed and patterns of dominance among ant species were described in order to assess (i) the relationship between thermal dependency and degree of behavioural dominance, and (ii) the relationship between dominance and discovery ability.

Ranging behaviour of the invasive crayfish, Procambarus clarkii (Girard)

The spreading of the invasive crayfish Procambarus clarkii throughout the world is attributed to human introductions; however, the rapid and widespread diffusion of the species following its establishment is the result of its dispersal capabilities. This study aimed to provide further information for the comprehension of the invasive potential of this crayfish by underlining some aspects of its behavioural flexibility. Radio-telemetry was used to analyse locomotion, home-range faithfulness and dispersal of the species in an Italian irrigation ditch system. Space was used differently by the two sexes, females being more nomadic in their ranging behaviour probably due to their reproductive phase. In addition, an inter-individual variability was found in both speed of locomotion and dispersal pattern. By applying a simulation model, it was shown that (1) both sexes disperse, and (2) ranging behaviour is not the result of a passive dispersion, but that the occupancy of burrows may affect the rate of dispersion. Finally, an intra-individual variability is related to the occurrence of two spatial strategies within the same population.

In situ and laboratory assessment of heart rate in a Mediterranean limpet using a noninvasive technique.

Heart rate of the Mediterranean limpet Patella caerulea L. was investigated on the natural shore and in the laboratory by using a technique based on infrared phototransducers. Field recording occurred in the Gulf of Trieste (northern Adriatic) during March and June 1997. A consistent dependence of heart rate on temperature was observed in limpets both when submerged and when exposed to air in the two periods, but thermal acclimation was evident. During spontaneous activity at high tide, heart rate increased 1.5–1.7 times the values observed during resting in water at corresponding temperatures. The dependence of heart rate on temperature (10°, 16°, and 22°C) and size (wet weight <1.25 and >1.30 g) in submerged limpets from different populations (northern Adriatic and Tyrrhenian) was tested in the laboratory by adopting a factorial design. The results showed a marked effect of temperature, body weight, and their interaction, independent from the site of origin. Smaller limpets showed a linear increase of heart rate in the whole range of temperature tests, while in the larger ones the increase between 10° and 16°C was greater than between 16° and 22°C. Heart rate decreased with increasing body size at control (16°C) and high (22°C) temperature, while at lower temperature (10°C) no effect of body size was evident. When removed from their home scar, limpets increased heart rate to about 1.5 times the reference value. Finally, correlation of oxygen consumption with heart rate of submerged limpets maintained at a different temperature (10°–22°C) was statistically significant.

Stable isotopes analysis to assess the trophic role of ants in a Mediterranean agroecosystem

1 Stable isotopes signatures (δ13C and δ15N) of the most important tree‐dwelling ants in an olive orchard were examined, together with the signatures of the most common herbivores, predators and sap‐sucking insects. The olive orchard consists of separate subunits (trees) surrounded by a matrix of grasses or bare ground, and the role of ants in such a system is not fully understood.

Food selection in freshwater omnivores: a case study of crayfish Austropotamobius pallipes

The omnivorous habit and food selection in freshwater macroinvertebrates was investigated in the white-clawed crayfish, Austropotamobius pallipes, a threatened species. First, during an annual cycle we analysed gut contents for vascular plant detritus, moss, amorphous plant material, and animal remains, and evaluated their organic content. Second, we ran preference experiments in the laboratory, in which crayfish had to choose, in the first trial among three vegetal items, in the second trial among three animal prey, and in the third trial between the two preferred items of the previous two trials (i.e. moss and insect larvae). Third, we analysed whether the assimilation efficiencies of different food items affected crayfish food choice. Our results revealed that this species mostly acted as a detritus consumer, obtaining nutrition from the associated microbes, fungi, proto- and metazoans, but also showed herbivorous and carnivorous habits. However, at least when food resources were not limited, crayfish displayed distinct feeding preferences, often ruled by factors other than the nutritional quality and the assimilation efficiency of the selected food.

Cardiac responses to salinity variations in two differently zoned Mediterranean limpets

Abstract Cardiac activity of two Mediterranean limpets was tested at different salinities. Patella caerulea inhabits the lower midlittoral where it is exposed to variations in salinity, while P. aspera experiences more stable salinity conditions in the infralittoral fringe. When exposed to moderate hypo- and hypersalinity (23 g l−1 and 43 g l−1) for 24 min, P. caerulea showed no significant variation in heart rate with respect to the control salinity (33 g l−1), while P. aspera exhibited a significant increase in heart rate in both conditions. This suggests a rise in metabolic rate due to activation of behavioural responses or physiological regulation. When exposed to extremely low salinity (3 g l−1) for 24 min, heart contractions ceased in most specimens of P. caerulea. A smaller number of specimens also displayed cessation of heart beat when exposed to extremely high salinity (63 g l−1). The heart beat resumed quickly in all specimens when they were returned to control salinity conditions. In contrast, cardiac activity was not interrupted in any of the P. aspera specimens at the 3 g l−1 and 63 g l−1 salinity levels, but strong bradycardia was evident. Contractile activity of the heart ceased in all specimens of P. caerulea and P. aspera when they were exposed to prolonged hypo-osmotic stress (3 g l−1 for 24 h). This acardia was largely reversible in P. caerulea, but most specimens of P. aspera did not recover from the treatment.

Glycogen content and rates of depletion in two limpets with different foraging regimes

Abstract The storage and utilization of glycogen reserves in the foot tissues of two Mediterranean limpets, Patella rustica L. and Patella caerulea L., were assessed in relation to the differences in their foraging regimes and zonation. No intraspecific difference was found in glycogen content in comparisons between late spring and winter, which roughly correspond to minimum and maximum gonadic development. No evident correlation with body size was detected within each species in both seasons. When comparing the glycogen content of fed specimens of the two species, a significant difference emerged, as concentrations in the foot of P. rustica were, on average, higher than those of P. caerulea in both seasons. When limpets were exposed to increasing periods of starvation (10–30 days) under controlled laboratory conditions, a marked difference between the two species emerged: P. rustica did not show any consistent variation in glycogen level, even after 30 days of starvation, whereas in P. caerulea, glycogen content declined exponentially as starvation proceeded. These findings agree with previous observations on the ecology and behaviour of the two species in the same area: the high shore P. rustica, which is naturally exposed to prolonged periods of starvation on account of the dependence of its foraging activity upon unpredictable and often infrequent favourable conditions (usually during rough sea), is able to store glycogen at greater concentrations, and has an efficient mechanism for saving energy during starvation. The low shore P. caerulea, which usually has a more regular foraging regime (being active at high tide on most days), stores glycogen at lower concentrations and shows a lower capacity to reduce energy losses when starved.

Investigating population dynamics in ungulates: Do hunting statistics make up a good index of population abundance?

Abstract Time series analysis plays an important role in the detection of mechanisms that drive population fluctuations. However, long time series are rare, with ungulate data sets usually not exceeding 50 years. In this article, we describe a long-term data set of population density indices of five ungulate species obtained from the analysis of bag records collected in the Castelporziano Preserve, Rome, Italy. Hunting statistics are often used as proxies for population density; however, in the case of long time series for large mammals, there are no comparative studies to assess the validity of such data. We evaluated the ungulate time series, using two different approaches: we 1) compared hunting statistics with independent animal counts, and 2) assessed whether or not habitat composition of the drive areas was representative of habitat availability in the whole estate. Regressions between bag data and animal counts gave significant results only for three species, whereas bag data corrected for hunted area were significantly correlated to animal counts for all five species. The results suggest that use of bag records not corrected for hunting effort and without any previous validation could lead to misleading estimates of abundance indices. Finally, our analysis showed that density indices of the five species were not significantly affected by the selection of habitats where hunting drives were organised. Our data set may contribute to the understanding of ungulate ecology in the Mediterranean environment.

Route Selection in The Foraging of Patella Vulgata (Mollusca: Gastropoda)

The prosobranch limpet Patella vulgata is an intertidal grazer performing looped excursions centred on a home scar. Foraging within each excursion is mostly concentrated around the point of maximum distance from home. The orientation of the foraging excursions in a group of limpets was analysed on a vertical substrate on a sheltered shore in North Wales. The spatial relationship between different excursions of the same individual was also analysed. A total of 174 complete excursions from 47 adult limpets were obtained using the LED (light emitting diode) tracking technique. In particular, the leaving direction and the direction of the main foraging area of each excursion were computed. When considering the foraging strategy over five consecutive days, a substantially radial cropping pattern was evident at both the population and individual level, with no evident directional preference. However, when considering consecutive excursions of the same individual a concordance in leaving directions was evident in about 40% of cases. The high overlap between the outward branch of the trajectory of one night and the homing branch of the previous one suggests that the directional decision can be based on a trail-following mechanism. Moreover, our data suggest that directional decisions are taken at the beginning of each excursion when leaving home.

Spatial patterns of the ant Crematogaster scutellaris in a model ecosystem

1. The spatial arrangement of individuals and populations may have deep influences on all the biotic interactions within a community.