Male reproductive tactics and female choice in the solitary, promiscuous bridled nailtail wallaby (Onychogalea fraenata)

Several behavioral studies of large, gregarious, and sexually dimorphic macropods have shown that males form dominance hierarchies and large males have the highest reproductive success. The bridled nailtail wallaby (Onychogalea fraenata) is a smaller and strongly sexually dimorphic macropod, but is also highly solitary and males do not form dominance hierarchies that are maintained temporally or spatially. Genetic studies of paternity have shown that large males are the most reproductively successful and only one-quarter of males sire offspring at any one time. The aim of this study was to investigate the tactics that males adopt to secure access to females at the time of estrus and to investigate whether females can influence which males have access to them. This study was conducted using 2 wild, free-ranging populations of bridled nailtail wallabies. Females in estrus were located and observed. and the total number of males present, the relative weight rank of each mate, and interactions between individuals were recorded. Females showed a preference for large males and incited male-male competition when the group of males present was large. Unlike other dimorphic macropods, fights among males were rare and were restricted to males of similar size. Large males gained access to females by guarding and following them closely and threatening other males who attempted to gain access. Smaller males spent less time with females, suggesting that small males may leave multimale groups in an attempt to locate unguarded females. Given the solitary nature of this species and the lack of a stable dominance hierarchy to influence male reproductive success. mate searching and mate guarding may be important male reproductive tactics in this species.

Does egg competition occur in marine broadcast-spawners?

When the availability of sperm limits female reproductive success, competition for sperm, may be an important broker of sexual selection. This is because sperm limitation can increase the variance in female reproductive success, resulting in strong selection on females to compete for limited fertilization opportunities. Sperm limitation is probably common in broadcast-spawning marine invertebrates, making these excellent candidates for investigating scramble competition between broods of eggs and its consequences for female reproductive success. Here, we report our findings from a series of experiments that investigate egg competition in the sessile, broadcast-spawning polychaete Galeolaria caespitosa. We initially tested whether the order in which eggs encounter sperm affects their fertilization success at two ecologically relevant current regimes. We used a split-clutch-split-ejaculate technique to compare the fertilization success of eggs from individual females that had either first access (competition-free treatment) or second access (egg competition treatment) to a batch of sperm. We found that fertilization success depended on the order in which eggs accessed sperm; eggs that were assigned to the competition-free treatment exhibited significantly higher fertilization rates than those assigned to the egg competition treatment at both current speeds. In subsequent experiments we found that prior exposure of sperm to eggs significantly reduced both the quantity and quality of sperm available to fertilize a second clutch of eggs, resulting in reductions in fertilization success at high and low sperm concentrations. These findings suggest that female traits that increase the likelihood of sperm-egg interactions (e.g. egg size) will respond to selection imposed by egg competition.

Sibling competition and parental control: Patterns of begging in parrots

Begging and food allocation patterns are the outcome of complex and repeated interactions between parents and young. In most systems studied, food allocation is regulated by begging and scramble competition. In contrast, little is understood about how nestling solicitation behaviours will evolve in systems where parents engage in complex patterns of food allocation. Parrots appear to be an excellent group in which to examine the shifting balance between sibling competition and parental control. Studies to date have shown that levels of sibling competition within parrot broods are low, possibly in response to parental control over food distribution. I assess what is known about the function of nestling begging in parrots and evaluate why begging signals appear to function differently in this group.

Begging and food distribution in crimson rosella (Platycercus elegans) broods: why don't hungry chicks beg more?

Altricial nestlings solicit food by begging and engaging in scramble competition. Solicitation displays can thus signal both hunger and competitive ability. I examined nestling solicitation and parental responses in crimson rosellas (Platycercus elegans), a species in which parents engage in complex patterns of food allocation and appear to control the distribution of food. By manipulating the hunger of individual chicks and entire broods, I assessed how chick behaviours and parental food allocation varied with hatching rank, level of hunger, and intensity of nestling competition. Last-hatched chicks begged more than first-hatched chicks irrespective of individual hunger levels. The two parents combined fed individually hungry chicks more, but mothers and fathers varied in their responses to begging chicks: fathers fed last-hatched chicks in proportion to their begging intensity, whereas mothers fed chicks equally. Since fathers generally allocate more food to first-hatched chicks, fathers appear to use begging rates to adjust food allocation to non-preferred chicks within the brood. When I manipulated brood hunger levels, begging rates increased for first- and last-hatched chicks suggesting that chick begging rates are sensitive to the level of competition. This study shows that begging by rosella chicks does not correlate with hunger in a straightforward way and that the primary patterns of food allocation by parents art: not influenced by chick begging. Thus the benefits of increased begging may be limited for nestlings in this species.

Habitat complexity, spatial interference, and "minimum risk distribution": a framework for population stability

In the past century, the debate over whether or not density-dependent factors regulate populations has generally focused on changes in mean population density, ignoring the spatial variance around the mean as unimportant noise. In an attempt to provide a different framework for understanding population dynamics based on individual fitness, this paper discusses the crucial role of spatial variability itself on the stability of insect populations. The advantages of this method are the following: (1) it is founded on evolutionary principles rather than post hoc assumptions; (2) it erects hypotheses that can be tested; and (3) it links disparate ecological schools, including spatial dynamics, behavioral ecology, preference-performance, and plant apparency into an overall framework. At the core of this framework, habitat complexity governs insect spatial variance. which in turn determines population stability. First, the minimum risk distribution (MRD) is defined as the spatial distribution of individuals that results in the minimum number of premature deaths in a population given the distribution of mortality risk in the habitat (and, therefore, leading to maximized population growth). The greater the divergence of actual spatial patterns of individuals from the MRD, the greater the reduction of population growth and size from high, unstable levels. Then, based on extensive data from 29 populations of the processionary caterpillar, Ochrogaster lunifer, four steps are used to test the effect of habitat interference on population growth rates. (1) The costs (increasing the risk of scramble competition) and benefits (decreasing the risk of inverse density-dependent predation) of egg and larval aggregation are quantified. (2) These costs and benefits, along with the distribution of resources, are used to construct the MRD for each habitat. (3) The MRD is used as a benchmark against which the actual spatial pattern of individuals is compared. The degree of divergence of the actual spatial pattern from the MRD is quantified for each of the 29 habitats. (4) Finally, indices of habitat complexity are used to provide highly accurate predictions of spatial divergence from the MRD, showing that habitat interference reduces population growth rates from high, unstable levels. The reason for the divergence appears to be that high levels of background vegetation (vegetation other than host plants) interfere with female host-searching behavior. This leads to a spatial distribution of egg batches with high mortality risk, and therefore lower population growth. Knowledge of the MRD in other species should be a highly effective means of predicting trends in population dynamics. Species with high divergence between their actual spatial distribution and their MRD may display relatively stable dynamics at low population levels. In contrast, species with low divergence should experience high levels of intragenerational population growth leading to frequent habitat-wide outbreaks and unstable dynamics in the long term. Six hypotheses, erected under the framework of spatial interference, are discussed, and future tests are suggested.

Economic competition and evolution: Are there lessons from ecology?

After generally discussing models in ecology and economics that combine competition, optimization, and evolution, this article concentrates on models of intraspecific competition. It demonstrates the importance of diversity/inequalities within populations of species and other environments for the sustainability of their populations, given the occurrence of environmental change. This is demonstrated both for scramble (open-access) and contest competition. Implications are drawn for human populations and industrial organization. The possibility is raised that within-industry competition may not always exist between firms in all stages of the development of a new industry. Policy implications are considered. For example, it is argued that policies designed to encourage intense business competition and maximum economic efficiency have the drawback of eventually making industries highly vulnerable to exogenous economic changes.

Parliament House Competition Model, Canberra

View of model for competition entry.

Parliament House Competition Drawings, Darwin

View of presentation drawings for competition entry.

Parliament House Competition Model, Darwin

View of model for competition entry.

Parliament House Competition Drawings, Darwin

View of presentation drawings for competition entry.

Parliament House Competition Model, Darwin

View of model for competition entry.

Parliament House Competition Model, Canberra

View of model for competition entry.

Heart rate, blood lactate and kinematic data of elite colts (under-19) rugby union players during competition

Physiological and kinematic data were collected from elite under-19 rugby union players to provide a greater understanding of the physical demands of rugby union. Heart rate, blood lactate and time-motion analysis data were collected from 24 players (mean +/- s((x) over bar): body mass 88.7 +/- 9.9 kg, height 185 +/- 7 cm, age 18.4 +/- 0.5 years) during six competitive premiership fixtures. Six players were chosen at random from each of four groups: props and locks, back row forwards, inside backs, outside backs. Heart rate records were classified based on percent time spent in four zones (>95%, 85-95%, 75-84%, <75% HRmax). Blood lactate concentration was measured periodically throughout each match, with movements being classified as standing, walking, jogging, cruising, sprinting, utility, rucking/mauling and scrummaging. The heart rate data indicated that props and locks (58.4%) and back row forwards (56.2%) spent significantly more time in high exertion (85-95% HRmax) than inside backs (40.5%) and outside backs (33.9%) (P < 0.001). Inside backs (36.5%) and outside backs (38.5%) spent significantly more time in moderate exertion (75-84% HRmax) than props and locks (22.6%) and back row forwards (19.8%) (P < 0.05). Outside backs (20.1%) spent significantly more time in low exertion (< 75% HRmax) than props and locks (5.8%) and back row forwards (5.6%) (P < 0.05). Mean blood lactate concentration did not differ significantly between groups (range: 4.67 mmol.l(-1) for outside backs to 7.22 mmol.l(-1) for back row forwards; P < 0.05). The motion analysis data indicated that outside backs (5750 m) covered a significantly greater total distance than either props and locks or back row forwards (4400 and 4080 m, respectively; P < 0.05). Inside backs and outside backs covered significantly greater distances walking (1740 and 1780 m, respectively; P < 0.001), in utility movements (417 and 475 m, respectively; P < 0.001) and sprinting (208 and 340 m, respectively; P < 0.001) than either props and locks or back row forwards (walking: 1000 and 991 m; utility movements: 106 and 154 m; sprinting: 72 and 94 m, respectively). Outside backs covered a significantly greater distance sprinting than inside backs (208 and 340 m, respectively; P < 0.001). Forwards maintained a higher level of exertion than backs, due to more constant motion and a large involvement in static high-intensity activities. A mean blood lactate concentration of 4.8-7.2 mmol.l(-1) indicated a need for 'lactate tolerance' training to improve hydrogen ion buffering and facilitate removal following high-intensity efforts. Furthermore, the large distances (4.2-5.6 km) covered during, and intermittent nature of, match-play indicated a need for sound aerobic conditioning in all groups (particularly backs) to minimize fatigue and facilitate recovery between high-intensity efforts.

Grazers and diggers: Exploitation competition and coexistence among foragers with different feeding strategies on a single resource

A mathematical model is presented that describes a system where two consumer species compete exploitatively for a single renewable resource. The resource is distributed in a patchy but homogeneous environment; that is, all patches are intrinsically identical. The two consumer species are referred to as diggers and grazers, where diggers deplete the resource within a patch to lower densities than grazers. We show that the two distinct feeding strategies can produce a heterogeneous resource distribution that enables their coexistence. Coexistence requires that grazers must either move faster than diggers between patches or convert the resources to population growth much more efficiently than diggers. The model shows that the functional form of resource renewal within a patch is also important for coexistence. These results contrast with theory that considers exploitation competition for a single resource when the resource is assumed to be well mixed throughout the system.

Patenting genetic materials' unresolved issues and promoting competition in biotechnology

This paper addresses the broader unresolved issues posed by the patenting of genetic materials that are central to dealing with the tension between the patenting and competition schemes, namely distinguishing between what has already been 'discovered' and economically useful innovations (including the thresholds for novelty and non-obviousness), the exclusion of some subject matter from patenting and the restrictions on access to genetic resources to facilitate further innovation. The possible solutions of raising the threshold patenting standards, taking advantage of international intellectual property law developments and compulsory licensing are examined as ways to ameliorate the possibly detrimental consequences of current genetic material patenting practices. (C) 2003 Elsevier B.V. All rights reserved.