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At least 1,531 records · Page 85Linked to original sources
PubMed2006

Size-dependent interactions inhibit coexistence in intraguild predation systems with life-history omnivory.

Growth in body size during ontogeny often results in changes in diet, leading to life-history omnivory. In addition, growth is often dependent on food density. Using a physiologically structured population model, we investigated the effects of these two aspects of individual growth in a system consisting of two size-structured populations, an omnivorous top predator and an intermediate consumer. With a single shared resource for both populations, we found that life-history omnivory decreases the likelihood of coexistence between top predator and intermediate consumer in this intraguild predation (IGP) system. This result contrasts with previous unstructured models and stage-structured models without food-dependent development. Food-dependent development and size-dependent foraging abilities of the predator resulted in a positive feedback between foraging success on the shared resource at an early life stage and foraging success on the intermediate consumer later in life. By phenomenologically incorporating this feedback in an unstructured IGP model, we show that it also demotes coexistence in this simple setting, demonstrating the robustness of the negative effect of this feedback.

Animals↗
PubMed2006

Gaping displays reveal and amplify a mechanically based index of weapon performance.

Physical prowess, a key determinant of fight outcomes, is contingent on whole-organism performance traits. The advertisement of performance, via display, is poorly understood because it is unclear how information about performance is encoded into display characteristics. Previous studies have shown that weapon performance (i.e., bite force) predicts dominance and reproductive success in male lizards. We tested the hypothesis that gaping displays by adult male collared lizards (Crotaphytus) can provide an index of weapon performance by exposing the major jaw-adductor muscle complex and that white patches at the mouth corners amplify this index. For territorial adult males, the breadth of the muscle complex, which is not correlated with body size, was a strong predictor of bite force. For nonterritorial yearling males and females, however, measures of body and head size predicted bite force. The patches are highly conspicuous, exhibit UV-reflecting properties within the visual range of lizards, and provide size-independent information about bite force only in adult males. We conclude that exposure of the muscle complex during gaping displays can provide rival males with a reliable, body-size independent, biomechanically based index of weapon performance, an index that the mouth-corner patches amplify. Indexes that transmit information through mechanistic links to performance are expected to be widespread among animals.

Animal Communication↗
PubMed2006

On testing the competition-colonization trade-off in a multispecies assemblage.

The competition-colonization trade-off has long been considered an important mechanism explaining species coexistence in spatially structured environments, yet data supporting it remain ambiguous. Most competition-colonization research examines plants and the dispersal-linked traits of their seeds. However, colonization is more than just dispersal because rapid population growth is also an important component of colonization. We tested for the presence of competition-colonization trade-offs with a commonly used artificial assemblage consisting of protozoan and rotifer species, where colonization was the ability of a species to establish populations in patches. By ranking species according to their colonization abilities and their pairwise competitive interactions, we show that these species exhibit competition-colonization trade-offs. These results reveal that the competition-colonization trade-off exists within nonplant assemblages and that even in a laboratory setting, species are constrained to be either good competitors or colonizers but not both.

Animals↗
PubMed2006

Ecological specialization and adaptive decay in digital organisms.

The transition from generalist to specialist may entail the loss of unused traits or abilities, resulting in narrow niche breadth. Here we examine the process of specialization in digital organisms--self-replicating computer programs that mutate, adapt, and evolve. Digital organisms obtain energy by performing computations with numbers they input from their environment. We examined the evolutionary trajectory of generalist organisms in an ecologically narrow environment, where only a single computation yielded energy. We determined the extent to which improvements in this one function were associated with losses of other functions, leading to organisms that were highly specialized to perform only one or a few functions. Our results show that as organisms evolved improved performance of the selected function, they often lost the ability to perform other computations, and these losses resulted most often from the accumulation of neutral and deleterious mutations. Beneficial mutations, although relatively rare, were disproportionately likely to cause losses of function, indicating that antagonistic pleiotropy contributed significantly to niche breadth reductions in this system. Occasionally, unused functions were not lost and even increased in performance. Here we find that understanding how the functions were integrated into the genome was crucial to predictions of their maintenance.

Adaptation, Biological↗
PubMed1975

Effects of alpha-tocopherol acetate on the swimming endurance of trained swimmers.

Well-trained, competitive swimmers were divided into two groups. Group A was given 900 IU alpha-tocopherol acetate daily for 6 months while group B was given placebos. A swimming endurance test was given before the start of supplementation and after 1, 2, 5 and 6 months. No difference in swimmers' endurance was observed between the two groups during the 6-month period. There was also no difference in postexercise serum lactic acid levels. Younger, less well-trained, competitive swimmers were also divided into two groups. Group A received 900 IU alpha-tocopherol acetate daily while group B received placebos. Swimming times for these swimmers were erratic, reflecting a lack of training. alpha-Tocopherol did not appear to have any effect on their swimming endurance.

Acetates↗
PubMed1989

Age differences in heart rate patterns during concentration in a precision sport: implications for attentional functioning.

Highly skilled young (M = 29.5 years) and older (M = 50.0 years) miniature golf players were observed in relaxed training and high-arousal competition rounds. Motor performance (number of shots), subjective ratings of anxiety, and heart rate were registered. Results showed a similar increase of arousal from training to competition for both age groups. However, the older group deteriorated in motor performance from training to competition, whereas the younger group played equally well on both occasions. Results from continuous measurement of heart rate indicated a deceleration during the concentration phases among the younger players, and the magnitude of deceleration increased from training to competition. In contrast, heart rate accelerated during training among the older players, the magnitude of the heart rate change decreasing from training to competition. This evidence suggests that the deterioration in motor performance observed in older players in stressful competitive activity may be due to age-related changes in attentional functioning.

Adult↗
PubMed1991

On the generalizability of the age-related decline in coping with high-arousal conditions in a precision sport: replication and extension.

Two field experiments are reported in which highly skilled miniature golf players varying in age were examined during training and competition (Swedish championships). Number of shots, heart rate, and subjective ratings of anxiety were registered. Results indicated that young and older adult players exhibited a similar increase of competitive anxiety from training to competition, as evidenced by both measures of arousal. In addition, whereas older players deteriorated in motor performance during competitive play, young players improved motor performance in competition. This pattern of results replicates and extends previous research. It is suggested that the data reflect age-related differences in the ability to cope with high-arousal conditions as a result of age-related deficits in task-relevant cognitive abilities.

Adaptation, Psychological↗
PubMed1994

Caregiving and employment: competing or complementary roles?

This study examines the potential benefits and costs of having both work and elder care responsibilities, based on interviews with 94 employed caregivers. For the majority of the respondents, the negative aspects of combining work and caregiving roles were outweighed by positive aspects, such as a sense of accomplishment, enhanced interpersonal relationships, and opportunities to compensate for limitations experienced in each of the separate roles. Workplace policies and programs considered most helpful by respondents were those which provided options for adapting work routines to complement caregiving responsibilities.

Adaptation, Psychological↗
PubMedDate not supplied

Mating systems and sexual selection in male-pregnant pipefishes and seahorses: insights from microsatellite-based studies of maternity.

In pipefishes and seahorses (family Syngnathidae), the males provide all postzygotic care of offspring by brooding embryos on their ventral surfaces. In some species, this phenomenon of male "pregnancy" results in a reversal of the usual direction of sexual selection, such that females compete more than males for access to mates, and secondary sexual characteristics evolve in females. Thus the syngnathids can provide critical tests of theories related to the evolution of sex differences and sexual selection. Microsatellite-based studies of the genetic mating systems of several species of pipefishes and seahorses have provided insights into important aspects of the natural history and evolution of these fishes. First, males of species with completely enclosed pouches have complete confidence of paternity, as might be predicted from parental investment theory for species in which males invest so heavily in offspring. Second, a wide range of genetic mating systems have been documented in nature, including genetic monogamy in a seahorse, polygynandry in two species of pipefish, and polyandry in a third pipefish species. The genetic mating systems appear to be causally related to the intensity of sexual selection, with secondary sex characters evolving most often in females of the more polyandrous species. Third, genetic studies of captive-breeding pipefish suggest that the sexual selection gradient (or Bateman gradient) may be a substantially better method for characterizing the mating system than previously available techniques. Finally, these genetic studies of syngnathid mating systems have led to some general insights into the occurrence of clustered mutations at microsatellite loci, the utility of linked loci in studies of parentage, and the use of parentage data for direct estimation of adult population size.

Animals↗
PubMedDate not supplied

Accumulation of transposable elements in the genome of Drosophila melanogaster is associated with a decrease in fitness.

Replicates of the two isogenic laboratory strains of Drosophila melanogaster, 2b and Harwich, contain different average transposable element (TE) copy numbers in the same genetic background. These lines were used to analyze the correlation between TE copy number and fitness. Assuming a weak deleterious effect of each TE insertion, a decrease in fitness is expected with an increase in genomic TE copy number. Higher rates of ectopic exchanges and, consequently, chromosomal rearrangements resulting in early embryonic death are also predicted from an increase in TE copy number. Therefore egg hatchability is expected to decrease as the genomic TE copy number increases. In 2b, where replicate lines have diverged up by 90 TE copies per haploid genome, a negative correlation between the number of TE insertions and both fitness and egg hatchability were found. Neither correlation was significant for the Harwich replicates, which have only diverged by 30 TE copies. The average deleterious effect of a TE insertion on fitness and its components was estimated as 0.004. Both homozygous and heterozygous TE insertions were shown to have deleterious effects on fitness and its components.

Analysis of Variance↗
PubMed2005

Asymmetrical competition and patterns of abundance of Aedes albopictus and Culex pipiens (Diptera: Culicidae).

We tested for competitive advantage among larvae of Aedes albopictus (Skuse) and Culex pipiens L. in a laboratory experiment and determined the frequency and spatial and temporal patterns of co-occurrence in the field in East St. Louis, IL. In a laboratory competition experiment at multiple combined densities of Ae. albopictus and Cx. pipiens larvae, Ae. albopictus survivorship and developmental times were significantly affected by conspecific densities but not by Cx. pipiens densities. In contrast, Cx. pipiens survivorship and developmental times were significantly affected by both conspecific and Ae. albopictus densities. Per capita rate of increase (r') for Ae. albopictus cohorts declined significantly due to density of conspecifics, but not density of Cx. pipiens. Interspecific competition between Ae. albopictus and Cx. pipiens under these laboratory conditions was strong and asymmetrical, with the effect of Ae. albopictus on Cx. pipiens much stronger than the reverse. In monthly samples from tire sites in East St. Louis, Ae. albopictus was highly seasonal, occurring in relatively low abundance from early May to July and increasing in abundance in August and September. Co-occurrence corresponded to the seasonality of Ae. albopictus, with Cx. pipiens encountering Ae. albopictus in more tires and at higher numbers within a tire, in August and September. Abundance of both species was high in residential areas and was unrelated to overstory cover, total nitrogen, and total phosphorus. Abundance of Ae. albopictus, but not of Cx. pipiens, was positively associated with conductivity. We expect Cx. pipiens to suffer from the effects of interspecific competition in tires in which it encounters Ae. albopictus. Interspecific competition between these species may be of both ecological and medical importance.

Aedes↗
PubMed2006

A scenario for invasion and dispersal of Aedes albopictus (Diptera: Culicidae) in New Zealand.

To date, there has been no confirmed, indigenously acquired case of arthropod-borne viral disease in New Zealand, but this may change in the near future due to the presence of exotic vectors and regular influx of infected humans. The risk of a disease outbreak may be aggravated if other exotic mosquito vectors become established, in particular Aedes albopictus (Skuse), a species that has already been intercepted several times in New Zealand. In this study, the possible means of invasion and dispersal of Ae. albopictus in northern New Zealand are discussed, along with the factors that should facilitate its establishment in the event it evades border controls.

Aedes↗