DAILY FORAGING ACTIVITY AND FOOD COLLECTION OF THE THERMOPHILIC CURSOR (, FORMICIDAE) X Cerda, J Retana, J Bosch, A Alsina

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X Cerda, J Retana, J Bosch, A Alsina. DAILY FORAGING ACTIVITY AND FOOD COLLECTION OF THE THERMOPHILIC ANT (HYMENOPTERA, FORMICIDAE). Vie et Milieu / Life & Environment, Observatoire Océanologique - Laboratoire Arago, 1989, pp.207- 212. ￿hal-03033917￿

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DAILY FORAGING ACTIVITY AND FOOD COLLECTION OF THE THERMOPHILIC ANT CATAGLYPHIS CURSOR (HYMENOPTERA, FORMICIDAE)

X. CERDA{1), J. RETANA J. BOSCH (2) and A. ALSINA{2) ' Departamento de Biologia , Biologîa Végétal y Ecologia, Facultad de Ciencias, Universidad Autônoma de Barcelona, Bellaterra, 08193 Barcelona, Espaha 121 Departamento de Biologia Animal, Facultad de Biologia, Universidad de Barcelona, c/Diagonal 645, 08028 Barcelona, Espaha

FOURMI RÉSUMÉ — L'activité de récolte et le régime trophique de la Fourmi Cataglyphis CATAGLYPHIS CURSOR cursor ont été étudiés sur une pelouse xérophyle sur la côte méditerranéenne. C. cursor REGIME ALIMENTAIRE ACTIVITE DE RECOLTE est une Fourmi zoonécrophage qui se nourrit principalement de cadavres d'Insectes, NICHE THERMIQUE surtout de Fourmis. La coopération entre les ouvrières pour le transport des proies est très rare, ce qui explique que le poids des proies ne surpasse pas celui que les ouvrières peuvent transporter individuellement. L'activité journalière est strictement diurne. Il s'agit d'une Fourmi très thermophile qui atteint son maximum d'activité lorsque la température est la plus élevée. Cette niche thermique constitue un grand avantage pour l'espèce car aux heures les plus chaudes, les autres Fourmis ne sortent pas et l'efficacité de la récolte des Cataglyphis est maximale.

ANT ABSTRACT — Foraging activity and diet of the scavenger ant Cataglyphis cursor have CATAGLYPHIS CURSOR been studied in a savanna-like grassland on the Mediterranean coast. C. cursor is a DIETARY SPECTRUM zoonecrophagous ant that collects mainly corpses of , specially . Coopé- FORAGING ACTIVITY THERMAL NICHE ration in food transport is very rare in this species so that the weight of items does not exceed what workers can drag individually. Daily activity is strictly diurnal. It is a highly thermophilic species whose greatest activity takes place when the température is highest. This thermal niche confers an important advantage to the species, because at the hottest times of the day, they are the only ants présent on the ground surface and its foraging efficiency is at its highest.

INTRODUCTION C. cursor piliscapa is found on the Mediterranean coast, from west of the Rhône and the whole Camargue to the proximity of Barcelona in . Cataglyphis cursor Fonscolombe is a Mediterra- In the last years, several studies on C. cursor have nean ant characterised by its relatively large size been published, dealing with the thelytokous par- (mean body length of workers 7.2 ± 1.8 mm, thenogenesis of its workers (Cagniant, 1979, 1980, Cagniant, 1983), its dark colour and fast movements. 1982; Lenoir & Cagniant, 1986); its distribution and From the systematic point of view, the group C. life cycle (Cagniant, 1976 a,b); intra and inter-colony cursor, including C. cursor var. cursor Fonsc, 1846, récognition by workers (Lenoir et ai, 1982; Lenoir, C. cursor vax. piliscapa Forel, 1901, and C. cursor var. 1984; Isingrini & Lenoir, 1984; Nowbahari & Lenoir, tibialis Bondroit, 1918, is now under review, and 1984); and several aspects of its foraging ecology in preliminary results indicate that the studied popu- the field (Pondicq, 1983; Retana et ai, 1984, 1986; lations of Canet de Mar should be assigned to the Bosch et ai, 1987). In this paper we shall describe variety piliscapa, probably to be regarded as a good the dietary spectrum and foraging activity of this ant species (Espadaler, pers. com). in the field. 208 CERDA, X. ET AL.

MATERIAL AND METHODS RESULTS AND DISCUSSION

This study has been carried out in Canet de Mar Dietaiy spectrum (40 km northeast of Barcelona, on the Catalan coast) in a grassland of Hyparrhenia hirta, one of the most As ail other species of the (Delye, 1968; disturbed communities of the original live-oak grove Harkness, 1977; Wehner et ai, 1983) C. cursor is a coastal ecosystem. zoonecrophagous ant that collects mainly corpses of During four years (1983 to 1986), on a total of 45 insects and other (Retana et al, sampling days, the activity and behaviour of C. 1986)(Table I). There are no significant différences cursor workers were observed and five nests were between three successive years (chi square test, monitored. At each nest entrance, the number of p < 0.001). Ants account for most of the diet of C. entries and exits was registered during the first ten cursor, which has also been observed in other species minutes of each hour on every sampling day. From of the genus (Harkness, 1979; Cerda, 1986). This is thèse data, the values for every hour and sampling in agreement with the fact that C. cursor workers day were calculated. The average mean of entries collect any dead they find (see below) and and exits has been used as an index of activity. that ants are the most abundant group in the area Besides, the following environmental parameters (Bosch et al., 1987). Other important groups in the have been hourly registered : température at the soil diet of the species are heteropterans and homopte- surface in the shade, température of the soil at rans, specially aphids which are collected in their différent levels, relative humidity and light intensity. period of greatest abundance (June). Other groups Items brought to the nest by workers of C. cursor of items usually account for less than 3 %, but seeds were collected for later identification and measure- (most of them of Centaurea aspera) attain higher ment in the laboratory. To ascertain whether or not percentages. there existed some food préférences on the part of the workers, they were offered différent types of Table I. — Number and percentage of each type of item items they could easily find in the field : dead brought to the nest by C. cursor workers in three consé- arthropods, dead snails, excréments of vertebrates, cutive years. plant remains and seeds. Responses were considered

positive when the ant seized the item and tried to N % N % N % N %

carry it to the nest, and négative when, after encoun- = Animal remains tering the item, the ant abandoned it having not Ants 128 53.1 323 47.4 114 53.0 565 49.7 Heteropterans ' fr 8.8 34 5.1 7 3.2 62 5 4 made any attempt to collect it. Homopterans Aphids s 3.3 69 10.1 15 7.0 92 8.1 Homopterans Others 2 0.8 19 2.8 2 0.9 23 2.0 Spiders 8 3.3 18 2.6 7 3.3 33 2.9 Présence of liquid food in the crop of workers Coleoptcrans 6 2.5 14 2.1 8 3.7 28 2.4 was studied by gently pressing their gaster as explai- Dipterans S 2.1 16 2A 6 2.8 27 2.3 Lepidopterans 3 1.2 6 0.9 3 1.4 12 1. 1 ned in a previous paper (Retana et al., 1986). Orthopterans 3 1.2 7 1.0 2 0.9 12 1.1 Other Hymenopterans 1 0.4 6 0.9 4 1.9 11 1.0 Censuses at liquid food sources (nectar of flowers Dictyopterans 1 0.4 1 0.1 2 0.2 Snails 1 0.4 7 1.0 3 1.4 II 1.0 and honeydew of aphids) were carried out every two Neuropierans - - 3 0.4 - - 3 03 Thysanopterans - - 2 03 - - 2 0,2 hours on previously marked plants of différent Psocopterans - - 2 03 - - 2 0.2 Diplopoda - 1 0.1 - 1 0.1 species. Unidentified remains 28 11.6 84 123 24 11.2 136 11.9 = Plant remains To compare the density of workers of C. cursor Seeds 18 7,6 53 7.8 14 6.5 85 7.5 Other 8 3.3 16 on the ground with regard to other ant species, six 2.4 6 2.8 30 2.6 squares of one m2 were laid out, and every two hours Totals: 241 100 681 100 215 100 1137 100 the number of ants of each species on each square was noted. According to Bosch et al. (1987), the dietary spectrum of C. cursor dépends on the interaction of We also distributed, ail over the study area, three factors : a) the simultaneity between the ap- several food items (mainly corpses of arthropods pearance of potential prey and the period of higher that could be carried by workers), and waited for an food requirements of colonies, b) the accessibility of ant to find and collect them. When this happened, this prey, and c) a certain sélection on the part of we noted the ant species and the time elapsed. This workers. Table II shows that there is no préférence way, foraging efficiency of C. cursor workers depen- between différent types of arthropods since those of ding on time of day and présence of other ants could hard cuticula such as coleopterans and hymenopte- be evaluated. rans, as well as those of soft integument such as orthopterans, dipterans and larvae, are equally accepted. They are only refused at the beginning of the season, when colony requirements are very low and items taken to the nest by workers are scarce. CATAGLYPHIS CURSOR : DIETARY SPECTRUM 209

Table II. — Items accepted or rejected by C. cursor FREQ workers in the field. 1SOj Type of item Accepted Rejected

Hard arthropods corpses 82 7 Soft arthropods corpses 84 8 Snails 16 15 Excréments of vertébrales 0 21 Plant remains 1 21 X-4 2mm Centaurea seeds 24 1 Centaurea seeds without elaisome 0 25 100 N-741 Other seeds 0 15

Results concerning snails, which are actively collected by other ants such as Aphaenogaster senilis 50 and Tapinoma nigerrimum, are not so clear : nearly half of the times they were offered to C.cursor workers, they triggered a négative response. The rest of items tested (excréments of vertebrates, plant remains and most seeds) are only very rarely ac- 11 13 15 cepted : workers walk onto them without paying them any attention. On the other hand, seeds of SIZE mm Centaurea aspera are always collected. However, when we removed the elaiosome placed at the base ACT B of the seed, they were ignored. From the point of view of ants, elaiosomes are analogous to 20 H corpses (Carrol & Janzen, 1973), which indicates that Centaurea seed collection by C. cursor is not a sign of granivory. 15 Besides the above-mentioned préférences, size of the items is another factor influencing its collection. Mean length of preys brought to the nest by C. cursor workers is 4.2 mm, with more than 95 % of the items 10 ranging from 1 to 8 mm and only 5 % between 8 and 15 mm (Fig. 1A). This is attributable to the fact that coopération in food transport is very rare in this species (Querard, 1985, and pers. obs.) so that a single worker is unable to carry prey exceeding a certain weight. Although body weight of C. cursor ranges from 2 to 15 mg (Cagniant, 1983), they can easily drag items of 50 mg (nearly up to 25 times its 20 30 40 50 own body weight for small ants). Heavier prey such TEMPERATURE as bees (about 60 mg) are only carried to the nest Fig. 1. — A, distribution of size (body length) of items with difficulty and provided the surface of the brought to the nest by workers of C. cursor. Y-axis : ground is more or less even and bereft of obstacles. frequency. X-axis : length in mm. Arrows indicate range Food items weighting more than 80-90 mg cannot be of body length of C. cursor workers. B, activity of C. cursor transported by individual workers, which end up by (Y-axis) as a function of open ground surface température abandoning the prey, that are eventually collected by (X-axis). Dots represent average mean values for each other ants of the area such as Aphaenogaster senilis température (for ten minutes). and Pheidole pallidula. The proportion of C. cursor workers that go back unclear. Workers of C. cursor are only occasionally to the nest with a solid item is relatively small found collecting nectar or honeydew. They only (13-27 %) in Canet de Mar (Retana et ai, 1986). This appear in considérable numbers on fennel plants low efficiency is normal in other insectivorous ants (Foeniculum vulgare) where they usually collect (Levieux, 1983; Cerda, 1986) which according to nectar (80 % of observed workers) and sometimes Carrol & Janzen (1973) is due to the fact that insect tend aphids of the species Aphis fabae (20 % of corpses are an unpredictable food source, both from observed workers). The number of foragers involved the point of view of location and quantity. in such duties is very small when compared with However, in C. cursor, many of the foragers that those of other more specialized ant species. For do not carry an item to the nest, do transport liquid instance, we found 50 workers of the nectarivorous food in their crops (50 % of them in 1984, Retana et ant Camponotus foreli on flowers, and nearly 600 ai, 1986). The origin of this liquid food is still workers of the aphids tending ant Camponotus 210 CERDA, X. ETAL.

ACT a sylvatkus tending aphids per every worker of C. TEMP cursor collecting the same types of food. 40- -50 The lack of correspondence between the high A i numbers of workers going back to the nest with 30 j j \ S filled crops and the scarcity of them at flowers or f I 40 £ j groups of aphids seems to imply the existence of \ '■. some other food source which has not been moni- 20 I » \ 30 tored. Harkness (1977) and Wehner et ai (1983) / / y \ Si report that many of the workers of Cataglyphis / / bicolor that brought liquid food to the nest licked 10- -20 î leaves, shoots and other plant surfaces. A similar J explanation could be given in the case of C. cursor, since foragers usually walk into the undergrowth, 7 9 11 13 15 17 19 21 but we have not observed such licking behaviour. ACT b TEMP 40- - Foraging activity 50

Seasonal activity of C. cursor has already been 30 i 40 described in a previous paper (Bosch et ai, 1987), ; \ where the influence of available food and of life cycle (présence of larvae increasing energetic requi- 20 /\ " 30 rements of colonies) on it is discussed. Seasonal activity starts, in Canet de Mar, at the end of March, 20 when mean températures rise to about 20°C and 10 colonies end hibernation. In the first months, from March to May, ants are not very active and collect few food items. In June and July, when larvae are 7 9 11 13 15 17 19 21 most abundant in nests, there is a strong increase in HOUR foraging activity. In August, values decrease consi- Fig. 2. — Two daily activity curves of a C. cursor colony derably until the end of the cycle in November when in 1985; (a) July 1, (b) July 24. Right scale : ground surface hibernation starts. température in the sun, in "C (dashed line). Left scale : activity measured as the average mean of entries and exits As far as daily activity is concerned, C. cursor is per ten minutes (solid line). X-axis : time of day. strictly diurnal ail through the season. Figure 2a shows a typical activity curve on a summer day : at about 9.00 a.m. (LST) workers open the nest en- (Fig. 1 B) drops below 28°C and above 53°C. Between trance, from 11.00 to 14.00 most foraging activity thèse values it increases as the température rises, takes place, then decreases until workers close the giving a régression line of ACT = 0.98 T - 27.98 (R nest entrance in late afternoon. Variation throughout = 0.7371, P< 0.0001). Thèse results are in agreement the day of open surface température is shown in the with those obtained by Delye (1967), who establishes same Figure. C. cursor is, as ail other species of the the température limits of C. cursor normal activity in genus (Delye, 1968; Harkness, 1977; Cerda, 1986), the laboratory between 18°C and 45°C, and the a highly thermophilic ant since its greatest activity critical température of the species at 48°C (53°C at takes place when open ground surface température ground surface température correspond to 46-47°C is highest. This pattern is unalterable along the at 0.5 cm above the ground, which is the température season. An exception of this rule is seen in figure that foraging ants sensé). 2b : on this unusual day there was a sudden drop The other ants of the area cannot withstand such of activity of the colony at midday (also observed high températures, so at the hottest times of day, C. in other nearby colonies) caused by high tempéra- cursor are the only ants présent on the ground ture registered at that time. This phenomenon, surface. This thermal niche confers an important unique in four years of field work in the study area, advantage to the species. Table III shows the shows that there exists an upper thermal limit for C. proportion of food items laid out on the ground that cursor, at least in Canet de Mar, the southern limit were collected by C. cursor workers at différent times of the distribution of the species, because such high of the day; they are also indicated the mean time températures are not attained in other areas where spent in finding them and the absolute and relative C. cursor occurs. abundance of the species with regard to other ants Among ail the environmental parameters registe- (measured at the squares). As we can see, in early red, open ground surface température is the one morning there are few C. cursor workers and they which has the highest corrélation with activity of the find few items. As the température increases, the species (R = 0.7286, P<0.001). C. cursor's activity proportion of items found by C. cursor rises as well CATAGLYPHIS CURSOR : DIETARY SPECTRUM 211

Table III. — Foraging efficiency of C. cursor workers die (Delye, 1967), confers a great advantage on them, depending on time of day and présence of other ants. Data since they are able to forage at times of day when from May 9, 1986. (1) time of the day (LST). (2), air there are probably plenty of corpses of insects killed température in the shade in "C. (3), number of prey by heat, and no other ants, which are obliged to seek collected by C. cursor workers and percentage (in brackets) of total prey offered in this hour. (4), mean time (± shelter in their nests. This places C. cursor in a standard déviation) spent in finding them (in seconds). (5), unique position among ail ant species co-occurring number of C. cursor workers found at six squares (lxl m) in the study zone.

and percentage that is represented of the total number of ACKNOWLEDGEMENTS — We are grateful to X. ants found there (in brackets). Espadaler (Bellaterra) and to A. Lenoir (Paris) who made helpful comments on a draft of the manus- Time of day Air température Items collected Mean time C. cursor cript. by C cursor workers counted (i) (2) (3) (4) (5)

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