Vacant Territory Research Articles

Dispersal of Common Shrews (Sorex Araneus L.): The Dream and “An Accident”

Understanding the processes that affect the dispersal distance is essential from perspective of ecology and evolution. It is essential to understand processes that affect dispersal distances. Dispersal distances can may depend on environmental and demographic factors and on the motivation of an individual. Effective dispersal results in the distribution of related genotypes in space. The distribution of pairwise distances between related common shrews (sibs and half-sibs) is characterized by a nonrandom increase in the number of relatives at distances up to 200 m. Aggregations of relatives are formed in a part of individuals dispersed in a random direction to the nearest available home rang (“stright-line search”). The distribution of all distances between relatives (up to 1200 m) is satisfactorily approximated by the straight-line search model and is not consistent with the “spiral search” model as it is; however, the best match can be achieved by combining these two search types. The latter model variant (“mixed search”) assumes that the population includes animals with different personal traits: “superficial” and “thorough” explorers. Thorough explorers search for a vacant territory employing the spiral search strategy and correspond to “dreamers” in the model describing the movement and habitat selection strategy (MHSS). If vacant territories are in deficit and the environment is favorable, dreamers move over long distances and become randomly distributed in space: a random dispersion of related genotypes was recorded at distances from 200 to 1200 m. Therefore, searches for a dream territory in combination with a shortage of vacant territories (an accident) result in a random dispersal of related genotypes within a radius of at least 1200 m. The combination of temporal aggregations of relatives and the dispersal of related genotypes over a vast area explain well the previously discovered combination of an excess of homozygous alleles and a high allelic diversity.

Patch-scale culls of an overabundant bird defeated by immediate recolonization.

Overabundant native animals cause a variety of human-wildlife conflicts that can require management to reduce their social, environmental, or economic impacts. Culling is an intuitively attractive management response to overabundance, but poor monitoring of results and costs means that evidence for successful outcomes is often lacking. Furthermore, many culls worldwide have been ineffective or counterproductive due to ecological release mechanisms or compensatory responses by the overabundant species. We completed a controlled, replicated, costed, and rigorously monitored experimental cull of the endemic Australian honeyeater, the Noisy Miner (Manorina melanocephala). Aggressive exclusion of birds from remnant woodland patches by overabundant Noisy Miners is listed as a Key Threatening Process under Australian conservation legislation due to its impacts on threatened birds. The problem is particularly prevalent in the highly modified agricultural landscapes of eastern Australia. The species impacts avian assemblages at low densities (0.6-0.8birds/ha) and at a subcontinental scale (>1million km2 ). Some ecologists recommend culling as the only management response capable of timely reversal of declines of threatened small woodland birds. We monitored Noisy Miner abundance before and for 12 months after a culling program and found that immediate recolonization from the surrounding landscape negated the impact of the cull. We hypothesize that this is due to a vacuum effect; whereby, birds resident in more marginal habitat around treatment patches move into the vacant territory post-cull. Modeled mean abundance of Noisy Miners declined by 22% in treatment sites compared to an increase of 4% in control sites in the post-cull period. Abundance in all sites, however, remained three to five times higher than published ecological impact thresholds. Return on investment analysis indicated no relationship between culling effort and reduction in Noisy Miner abundance. We conclude that culling at a patch scale is not an efficient method of reducing Noisy Miner abundance to levels unlikely to impact threatened woodland birds in the highly modified study landscape, despite estimated costs 18 times lower than another potential management response of revegetation. Our study highlights the importance of building empirical evidence before intuitively attractive but not necessarily ecologically effective management responses are applied more widely.

Territory settlement in common loons: no footholds but age and assessment are important

Many animals face the task of locating and settling on a territory where they can produce offspring. Over the past 36 years, theoretical and empirical studies have provided growing support for the ‘foothold hypothesis’, which attempts to explain territorial settlement of long-lived animals. The hypothesis maintains that a young prebreeder lives within or intrudes into a cluster of breeding territories, accumulates site-dependent dominance there, then outcompetes other prebreeders for a territory within the cluster when it becomes available. We examined patterns in territorial intrusion and settlement among prebreeders of known age and natal origin to test the foothold hypothesis in the common loon, Gavia immer. We tested two other hypotheses for territory settlement: the maturation hypothesis, which posits that animals await physical and/or behavioural maturity before territory acquisition; and the assessment hypothesis, which maintains that prebreeders intrude into territories to assess fighting ability of territory owners, one of which they ultimately evict. We found no evidence for footholds in loons: prebreeders focused their intrusions within roughly 10 clustered territories, but intruded infrequently into the lake on which they later settled. Furthermore, prebreeders that waited years to usurp a territory had reproductive success no different from those that settled more rapidly on a vacant territory. The maturation hypothesis, in contrast, was supported in both sexes: prebreeders showed a sharp increase in fighting ability with age, and males exhibited age-related increases in mass and tendency to confront territory owners. The assessment hypothesis also gained support because intruders interacted extensively with owners and intruded frequently after territorial turnovers. Our study adds to a small but growing number of studies that fail to support the foothold hypothesis for territory settlement and support the conclusion that modes of territory acquisition might be more varied than previously thought.

Exploring juvenile golden eagles' dispersal movements at two different temporal scales

The spatial distribution of populations is the result of individuals' movements. In territorial species, the spatial dynamics of populations is to a large degree shaped by individuals' ranging behaviour during their juvenile dispersal. Here we use information on juvenile golden eagles (Aquila chrysaetos) tracked by satellite telemetry, to explore the effects of daily behavioural decisions on their dispersal strategy during their first year of life. When analysed on a biweekly basis, the large-scale movements of golden eagles did not differ from a correlated random walk (CRW) model of dispersal. Although in the long term such a strategy maximises the acquisition of information on good hunting areas, finding a mate and a vacant territory in a landscape, it is expensive in terms of energy requirements. At the finer scale of daily foraging movements, movement patterns were non-random, probably reflecting animals' oriented movements towards sites with high chances of successful hunting. We suggest that the key issue to take into account when exploring the factors determining individuals' dispersal strategies is how strongly the daily movements are influenced by an active search for food. This is to a large degree determined by food availability and individuals' ability to accumulate reserves. In our case, the individuals with the lowest proportion of foraging habitats within their dispersal areas showed large-scale movements more restricted than expected from a CRW. Also, distances covered by individuals in their biweekly movements were both larger and more variable in winter, when food availability diminishes.

Contest outcome in a territorial butterfly: the role of motivation

In many butterfly species, males compete over areas advantageous for encountering females. Rules for contest settlement are, however, largely unknown and neither morphological nor physiological traits can reliably predict the contest outcome. Here, we test the hypothesis that contests are settled in accordance with a motivation asymmetry. We staged contests between males of Pararge aegeria and after removing the resident, the non-resident was allowed (i) either to interact with a non-receptive female for 30 min (n = 30) or (ii) to spend 30 min alone in the cage (n = 30), after which the initial resident was reintroduced. The results show that males that had interacted with a female had a higher probability of becoming dominant and reversing contest outcome. Moreover, males that were faster to take over a vacant territory when the resident was removed were more likely to become dominant. Here, we show for the first time, to our knowledge, that frequent encounters with a mated female can increase male motivation to persist in a territorial contest in a butterfly. Further, we suggest that variation in intrinsic motivation reflects male eagerness to take over vacant territory. This study indicates that variation in resource value and motivational asymmetries are important for settling contests in butterflies.

The First Case of Successful Breeding of a Golden EagleAquila chrysaetosTracked from Birth by Satellite Telemetry

The natal dispersal of a Golden Eagle from its natal eyrie to the site where it reproduced for the first time was monitored. After covering > 16 000 km2 in its three years of juvenile dispersal, and despite flying > 130 km from its natal site, the eagle finally settled in a vacant territory just 26 km away from the place where it had hatched. Almost 95% of the total dispersal area was visited for the first time during the first year of tracking; less than 40% of the dispersal area was used during the remainder of the dispersal period. During dispersal the eagle regularly visited territories occupied by adult Golden Eagles. Previous records of the occupancy of the territory the eagle currently occupies show an alternation between periods when it remained vacant with periods when subadults occupied it. Although the other member of the breeding pair is also a subadult eagle, the birds managed to raise two fledglings.

Controlling sales force turnover costs through optimal recruiting and training policies

Although some sales force turnover has been shown to be desirable, too high a turnover rate has adverse consequences on the sales organization, is costly, and should be controlled. This paper shows that under typical circumstances, over a certain period of time, no firm can reasonably expect to always have exactly the number of salespeople it desires. In most cases, a firm may have more salespeople than it needs, and bear the associated costs of idle personnel, or too few sales representatives with the related vacant territory costs. This paper shows that (1) these costs are related to the length and costs of new salespeople’s recruiting procedures and training programs, and (2) management can minimize them by devising proper policies about the frequency of new salespeople recruiting campaigns and about the size of the various new recruit cohorts. Data requirements and implementation issues are discussed.

Bone: formation by autoinduction. 1965.

Bone: formation by autoinduction. 1965.

Evidence that helping at the nest does not result in territory inheritance in the Seychelles warbler.

In an environment that has a shortage of territories, helping to rear younger siblings ('alloparenting') is proposed to facilitate territory acquisition in two ways: (i) through group augmentation that leads to an increase of the territory with subsequent partial inheritance (budding); and (ii) through site dominance that leads to greater success when competing for the natal or a nearby territory after the death of the territory owner (complete territory inheritance). Most young Seychelles warbler (Acrocephalus sechellensis) males either show alloparenting or budding behaviour. Future budders had significantly more aggressive interactions with neighbours and assisted their parents more with territory defence than similarly aged future alloparents or non-helpers. This led to an increase of the natal territory of future budders before actual budding took place, whereas the natal territories of future alloparents remained constant in size. Alloparents never became budders and vice versa, refuting partial inheritance as an advantage of alloparenting. Natural male breeding vacancies were never inherited by alloparents born on vacant or other territories, but were inherited by budders born on the vacant territory or, if these were absent, predominantly by budders from neighbouring territories. We offer explicit experimental evidence against the 'helping at the nest to inherit' hypothesis. Experimentally created male breeding vacancies, with both a male alloparent and a similarly aged sibling budder present simultaneously in the vacant territory, were filled by budders only. Site dominance over territory inheritance is linked to budding and not to alloparenting.

Contest behavior in territorial male butterflies: does size matter?

Although intrasexual contests generally favor bigger or stronger individuals, the relevance of body size to war of attrition-type disputes between weaponless animals such as butterflies is unclear. In this study I aimed to investigate the significance of size in this context by studying territorial contests in Hypolimnas bolina (L.), a species that exhibits consistent seasonal plasticity in body size. In this species adult age is positively correlated with large size in spring but with small size in autumn. This shift allowed independent evaluation of the relevance of each variable (size and age) to intrasexual contest success. Observation of a population of marked individuals indicated that only age appeared important, with the winners of pair-wise contests significantly older than losers in both seasons, and with contests lasting longer when the age difference between the combatants was small. Age was also linked to residency; residents won 99% of all contests. This study suggests that size does not matter in these aerial disputes, but age and residency do. It is not yet possible to determine whether older butterflies are intrinsically better competitors, or whether they simply have greater opportunity to find a vacant territory.

Spacing patterns and territoriality of the stone marten

Sixteen stone martens (Martes foina) were intensively radio-tracked in central Italy in order to assess their spacing patterns. Home-range sizes and distances travelled per night were analysed with respect to sex, age, season, and habitat. Intrasexual territoriality is confirmed for the species; home-range edges appeared to be determined by the dispersion of neighbours' territories. Home-range size was positively correlated with the presence of woodland (less abundant and more dispersed resources). Males travelled longer distances than females, although home-range sizes did not differ significantly by sex; males did not move more during the rutting season than in other seasons. Subadults were tolerated by adults for varying periods, then in some cases they started an exploring phase before settling into a vacant territory. Stone martens' spacing patterns were affected by sex, age, social interactions, and resources. In particular, social patterns appear to be a key influencing factor, as territoriality, parental behaviour, mating interactions, and dispersal of young can account for site fidelity, dispersion of home ranges, and distance travelled. In particular, our data indicate the importance of the extended relationship between the mating pair, which is probably related to male parental investment, in determining the spacing patterns of the species.

AVIAN REMOVAL EXPERIMENTS: DO THEY TEST FOR HABITAT SATURATION OR FEMALE AVAILABILITY?

The classical test for habitat saturation and the existence of floaters in birds involves removing territorial individuals and documenting whether replacement occurs. In most experiments with birds, only males are removed. An alternative explanation for the observed reoccupation of vacant territories by males is that they are attracted by the presence of unmated (widowed) females, and not necessarily by availability of habitat. We performed experiments with a migratory passerine bird, the Black-throated Blue Warbler (Dendroica caerulescens), at the Hubbard Brook Experimental Forest, New Hampshire, in which we removed (1) only males, (2) only females, and (3) both males and females from breeding territories. In all cases when only males were removed, new or neighboring males colonized the vacant territory, whereas when both sexes were removed only one of nine territories was reoccupied; when females were removed, there was no replacement. Our results suggest the importance of considering female availability, in addition to habitat availability, in studies of habitat distributions and population dynamics of birds and other species.

Lek formation in sage grouse: the effect of female choice on male territory settlement

Previous studies of female choice in sage grouse, Centrocercus urophasianus, have identified two processes that could drive the local clustering of male territories at leks: (1) fidelity of females to previous mating sites (‘temporal spillover’ hypothesis), and (2) ‘spatial spillover’ of matings from an attractive male to his immediate neighbour (‘hotshot’ hypothesis). The effects of each process on male territory settlement were investigated using observations of the resettlement of vacant territories and of individual site fidelity during a 7-year field study. The frequency with which vacant territories were resettled both within and between seasons increased with mating success of the site's previous occupant, but not with the success of neighbouring males. Territories vacated by the most successful males acted as foci for clusters of territories in the following year. Fidelity of males to their territories within seasons also increased with their previous mating success, but was unaffected by the mating success of neighbours. However, between seasons the rate at which males returned to the lek (though not necessarily to the same territory) increased with both their own previous mating success and that of neighbours. Returning neighbours of males that failed to return were at an advantage in competing for the vacant territory. These data support the role of temporal spillover in lek formation and also suggest that territorial males use a ‘win-stay’ rule that should favour the use of established males as cues to settlement by naive individuals. The spatial spillover hypothesis was not supported, perhaps because this process creates conflicts of interest between attractive males and kleptoparasitic neighbours that prevent the formation of stable groups.

The oblique muscle organizer in Hirudo medicinalis, an identified embryonic cell projecting multiple parallel growth cones in an orderly array

The oblique muscle layer in the leech body wall is built upon the processes of a unique identified embryonic cell, the Comb- or C-cell. Each C-cell is composed of a spindle-shaped soma that projects approximately 70 parallel processes through the developing body wall at an angle oblique to the long axis. The morphogenesis of this cell and the navigation of its growth cones were examined by intracellular dye filling and antibody staining. At the earliest stages described each C-cell had about six processes, with those near the center of the cell oriented obliquely. As processes were added at the axial ends of the soma they often projected along previously developed longitudinal or circular muscle founder cells and then secondarily aligned themselves parallel to the older processes from the same C-cell. All growth cones initially extended to a particular location in the body wall, where they ceased growing until all 70 processes had been added (over the course of about 5 days). As adjacent segmental homologs met, their growth cones intermingled, eventually sorting out to align parallel. When one of these cells was ablated early—but not later—in development, the remaining adjacent segmental homologs expanded into the vacant territory, consistent with a hypothesis of mutual avoidance between segmental homologs. Most processes that expanded into the experimentally induced vacancy remained correctly oriented and parallel; the few exceptions projected instead along the mirror-image trajectory. Thus, expression of specific avoidance between adjacent C-cell processes is developmentally regulated and functions as a guidance mechanism in vivo, in that it serves to restrict possible trajectories. After aligning its growth cones, each cell stopped adding processes and the processes rapidly extended in concert along relatively precise trajectories. Processes of contralateral homologs cross to form the orthogonal grid used as a scaffold by myocytes to form the oblique muscles. The advancing fronts of growth cones reached the dorsal midline at about the same time as body closure occurs (at about Embryonic Day 20) at which time the C-cells became granular, lost processes, and presumably died. This sequence of developmental events is consistent with temporal and spatial regulation of different morphogenetic strategies, including—but not limited to—specific avoidance, and further suggests testable hypotheses of mechanisms of growth cone navigation in the intact embryo.

Identifying Sources of Turnover Costs: A Segmental Approach

The author proposes an analytical framework for assessing the costs of various sources of salesforce turnover (promotions, voluntary leaving, firing, and uncontrollable turnover) for salespeople with given characteristics (age, tenure, education, etc.). The main costs of salesforce turnover are taken into account, especially the costs of separation, recruiting and selection, training, vacant territory, and skill differential, as well as operating costs. Because the proposed procedure can be applied to any subgroup of salespeople, managers can use it to select the salesforce segments that are the most promising in terms of cost savings and can design specific turnover-reducing programs for those segments. The procedure is illustrated with a case study.

Strengthening of synaptic inputs after elimination of a single neurone innervating the same target.

The problem of 'competition' between neurones innervating the same target can be studied in simple neural systems such as the central nervous system of the leech and the lobster neuromuscular junction. Intracellular injection of pronase to kill selectively a single neurone shows that, in the leech, removal of one neurone is a sufficient signal to produce compensatory changes. After removal of a given neurone, only neurones of the same function respond to innervate the 'vacant territory'. This was shown both for a motor neurone (annulus erector) and sensory neurones (T or N). Thus the response is very specific. The lobster neuromuscular junction, with its multiple excitatory and inhibitory innervation, has advantages for the study of changes in synaptic efficacy of the remaining neurones after removal of a defined neurone releasing the same or a different transmitter. Killing the inhibitory neurone produced prolongation of the excitatory synaptic current because of a prolonged channel open time. When an excitatory axon is killed the remaining excitatory axon releases more transmitter. Over a period of 10 days, there is first a strengthening of existing synapses, then the appearance of new release sites and sprouting. Only those terminals of a neurone that innervate a territory with reduced innervation become stronger, while other terminals of the same axon remain normal. Cutting of axons produces different responses from those seen after killing single neurones.

The role of an acoustic display in territorial maintenance in the pika

Field experiments were performed on pikas (Ochotona princeps) to determine the role of their short call in the maintenance of territories. Removal of a resident resulted in significant increase in intrusions by adjacent pikas and the persistence of the intruder within the vacant territory. However, replacing a removed resident with its short call was effective in preventing a significant increase in intrusions.