Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: John Alcock x

John Alcock

Abstract

Lekking males of the carpenter bee Xylocopa (Neoxylocopa) varipuncta compete for landmark territories, where they are occasionally visited by receptive females. In a study conducted over three flight seasons, less than 10% of marked males qualified as long-term residents (i.e. bees that held the same hovering station for 90 min or more on at least two afternoons). However, among the small minority of long-term residents were some bees that returned to the same landmark for up to 3 hr every afternoon for several weeks. These males defeated many intruders in aerial combat during each afternoon. The hypothesis that site-faithful males were individuals of unusual resource-holding power is not supported. Long-term residents were not larger on average than short-term territory holders. Moreover, the frequency of mating by long-term residents was very similar to that of males in the general population, suggesting that long-term residents did not hold territories that were exceptionally attractive to females. Thus, the basis for site fidelity in this species remains elusive. The rarity of site-faithful males in this species may be related to great daily fluctuations in the numbers of potentially receptive females visiting the landmark territories, which may make the timing of male mate-attracting behavior far more important than regularly returning to defend any one site.

John Alcock

Abstract

This paper describes an experiment on interspecific differences in the response of bird predators to an artificial Batesian mimic/model complex. Black-capped chickadees (Parus atricapillus) and white-crowned sparrows (Zonotrichia leucophrys) were offered a series of 24 pairs of models and mimics after an initial presentation of the emetic model (a 1/2 mealworm adulterated with quinine sulphate and with a black dot painted on it). Chickadees attacked many mimics (unaltered 1/2 mealworms) and a few models. White-crowned sparrows attacked few mimics and almost no models. Differences between species in the manner of preparing mealworms for consumption may have contributed to the interspecific differences in the treatment of the series of model/mimic pairs. Perhaps more importantly, the chickadees, as opportunistic feeders dependent on a wide variety of prey, may possess special tolerance to noxious stimuli. The sparrows, conservative feeders with a more limited range of prey species, need not possess this tolerance in order to exploit their niche fully. Interspecific differences in feeding behavior could contribute to the origin and perfection of Batesian mimicry.

John Alcock

Abstract

The solitary wasp Cerceris simplex exhibits a variety of social interactions. In a nesting aggregation of this species females often abandoned old nests (voluntarily and involuntarily) and attempted to usurp burrows occupied by other females. These attempts were sometimes successful although they often failed forcing the searching female to hunt for still another burrow. Alternatively two or more wasps might provision the same nest for varying periods of time. It may be that nest-stealing behaviour has been, in some cases, a preliminary stage to the evolution of semi-social colonies in the Hymenoptera. This behaviour increases the probability that a female will try to enter and provision an already occupied nest; if the would-be parasite and the original occupant tolerate one another they could enjoy a variety of advantages through mutual occupation of a nest, including a reduction of the incidence of nest usurpation by other conspecifics.

John Alcock

Abstract

Sixteen red-winged blackbirds (Agelaius phoeniceus) were given an opportunity on each of four consecutive days to search for food items partly hidden in a wooden "food maze". The birds were divided equally into four groups. Each group on Days 1 and 2 of the experiment hunted for one of two baits placed on one of two separate rows of holes in the food maze (either sunflower seed bits in the lower row or seeds in the upper row or mealworm halves in the lower row or mealworms in the upper row). On the second day of the experiment the birds' foraging efficiency had usually improved with the redwings requiring less time to find ten baits. This improvement was linked to the adoption of a long distance scanning strategy which replaced the birds' initial tendency to inspect each hole at close range. On the third day of the experiment the birds were offered the same food item as on Days 1 and 2 but this time equally distributed in the upper and lower rows instead of entirely in one or the other. The redwings' previous experience affected their searching pattern. Birds that had been hunting and finding food only in the upper row continued to concentrate their efforts there. Birds that had been offered food in the lower row of holes initially took several baits there before switching to the upper row baits. On the fourth day of the experiment birds were offered two baits instead of just one. Again previous experience biased the searching behavior of the birds. Redwings that had on earlier days been hunting solely for mealworms usually removed many larvae before finding their first sunflower seed bit. Birds that had been searching for seeds quickly took several before switching to mealworms. It appears likely that redwings are sensitive to both locational and visual cues associated with prey and learn to use them while foraging. These results were discussed in the context of L. TINBERGENS search image hypothesis.

John Alcock

Abstract

Males of Paltothemis lineatipes defend stream-edge territories several meters in length. Receptive females fly to the stream to oviposit in very small patches of barely submerged fine gravel; each territory contains at least one but rarely more than two patches. Territorial males intercept incoming gravid females, copulate very briefly with them while hovering over a potential oviposition site, and then release their partners, which usually oviposit for less than 2 min before leaving the stream. Because mated females do not oviposit while in tandem with a male, neighboring territory owners sometimes succeed in stealing females before they have completed oviposition in their first mate's territory. Interrupted females sometimes are receptive, and may copulate with an intruder and oviposit in his territory. Gravid females arrive at the stream primarily in a 3 h mid-morning period during which time the density of territorial males is greatest. Fights for territories are most frequent early in the daily activity cycle, just prior to the time when receptive females are most likely to appear. There are many more males than sites with suitable oviposition substrate. Consequently competition for territories is intense, particularly at locations that attract relatively many females. From 2-4 males may claim favored territories in sequence on a given day, with the same males returning to partition ownership of the location temporally in the same order over several days. Temporal partitioning of certain territories in P. lineatipes appears to be a consequence of the males' ability to identify superior locations and superior times for territoriality, with the result that no one individual can monopolize a productive site for an entire daily flight period.

John Alcock

Abstract

(I) Some males of the pompilid wasp Hemipepsis ustulata defend territories in the crowns of palo verdes and other trees and bushes located high on the crest of mountain ridges. During the month of May in central Arizona territorial wasps remained at their stations for as many as 5 hr after sunrise; several individuals held the same site for more than two weeks. (2) Many palo verdes were never claimed despite the fact that large numbers of wasps visited trees held by other males and would occupy territories from which resident males had been experimentally removed. (3) Territory owners tended to be larger than non-territorial visitors, atlhough some small males in this highly variable species were able to hold certain territories for 2 or more days. (4) Palo verdes that were on or very close to peaktops along a mountain ridge were preferred territories. Prolonged clashes for possession of a tree were observed only at these sites. When resident males were removed from a number of trees along an ascending ridge, the higher trees were taken by newcomer males more quickly than the lower ones. (5) Relatively large males were found in preferred territories. In general, the closer a territory was to a peaktop, the larger the resident male. Smaller wasps either visited many territories as intruders or they established residence in trees below the preferred peaktop sites.

Ronald L. Rutowski and John Alcock

Abstract

1. Females of the solitary bee, Nomadopsis puellae, foraging for pollen at flowers will copulate with any male that can reach them but the duration of copulation is not constant over the daily foraging-mating period (which lasts from about 0900-1300). Early on, copulations are brief (usually less than 1 min). As the morning progresses, males tend not to release their mates spontaneously but remain in copula for as long as it takes a female to collect a full pollen load and return to her nest. In addition, late in the mating period males that have not secured a single female may begin to assault pairs in attempts to usurp a female from a copulating male. 2. We propose that males control the duration of mating in ways that reflect a change in the genetic gains associated with brief versus prolonged copulations over the course of the morning. We assume that sperm precedence occurs in this species and that females are more likely to oviposit at the end of the foraging period than at the beginning. If these assumptions are correct, guarding a mate through prolonged copulation could become increasingly advantageous as the mating period draws to a close each day. Given a high degree of competition for mates, a male that secured a female on her last trip of the morning could greatly improve the chance that his mate would use his sperm for fertilization if he prevented other males from reaching her until she was safely back inside her nest burrow. 3. An alternative hypothesis that the variation in copulation length is due to changes in the readiness of females to receive sperm from a male over the mating period is considered. Limited data suggest that females do not signal degrees of sperm receptivity to males. Males probably determine how long they will copulate, switching from the tactic of securing many short (unguarded) copulations to a few lengthy (guarded) matings in the course of a morning.