Obligately cooperative breeders (cooperators) display a negative growth rate once they fall below a minimum density. Constraints imposed by natural enemies, such as predators or competitors, may push cooperator groups closer to this threshold, thus increasing the risk that stochastic fluctuations will drive them below it. This may indirectly drive these groups to extinction, thereby increasing the risk of population extinction. In this paper, we construct mathematical models of the dynamics of groups of cooperators and non‐cooperators in the presence of two types of enemies: enemies whose dynamics do not depend on the dynamics of their victim (e.g., amensal competitor, generalist predator) and those whose dynamics do. In the latter case, we distinguish positive (e.g., specialist predator) and negative (e.g., bilateral competitor) reciprocal effects. These models correspond to the classical amensal, predation and competition models, in the presence of an Allee effect. We then develop the models to study consequences at the population level. By comparing models with or without an Allee effect, we show that enemies decrease the group size of cooperators more than that of non‐cooperators, and this increases their group extinction risk. We also demonstrate how an Allee effect at a lower dynamical level can have consequences at a higher level: inverse density dependence at the group level generated lower population sizes and higher risks of population extinction. Our results also suggest that demographic compensation can be achieved by cooperators through an increased intrinsic growth rate, or by decreasing the enemy constraint. Both of these types of compensation have been observed in empirical studies of cooperators.
Craniofacial conditions are mainly treated within England by four supra-regional centres. Due to a continuous increase in the number of cases referred to our service we audited the source and nature of these referrals. Data was prospectively collected over a four-year period from April 2004 to March 2008. The speciality of the referring clinicians was recorded, along with the diagnosis. A year-by-year increase in the number of referrals from 138 in 2004–2005 to 253 in 2007–2008 was seen. There was a 214% increase in the number of patients referred with single suture craniosynostosis, a 520% increase in patients with benign hyperplastic conditions such as fibrous dysplasia, neurofibromatosis and vascular anomalies and a 220% increase in patients treated elsewhere but now needing revision surgery. A 407% increase in referrals for positional plagiocephaly was recorded. Our referral pattern reflects the internationally accepted increase in the incidence of metopic synostosis and positional plagiocephaly. Due to the skill mix and experience present in a designated craniofacial service other benign hyperplastic and hypoplastic conditions are increasingly being referred. Additional referrals have come from a change in the referral pathway. To manage the increased workload we have established separate clinics to manage vascular anomalies and have adopted a policy of not reviewing patients with positional plagiocephaly.
1. The aim of this study was to derive and evaluate a priori models of the relationship between annual instantaneous population growth rate (r) and climate. These were derived from the numerical response of annual r and food, and the effect of climate on a parameter in the numerical response. The goodness of fit of a range of such deductive models to data on annual r of Soay sheep and red deer were evaluated using information-theoretic (AICc-based) analyses. 2. The analysis for sheep annual r showed negative effects of abundance and negative effects of the interaction of abundance and climate, measured as March rainfall (and winter NAO) in the best fitting models. The analysis for deer annual r showed a negative effect of deer abundance and a positive effect of climate measured as March rainfall (but a negative effect of winter NAO), but no interaction of abundance and climate in the best fitting models. 3. There was most support in the analysis of sheep dynamics for the ratio numerical response and the assumption that parameter J (equilibrium food per animal) was influenced by climate. In the analysis of deer dynamics there was most support for the numerical responses assuming effects of food and density (Ivlev and density, food and density, and additive responses) and slightly less support for the ratio numerical response. The evaluation of such models would be aided by the collection of and incorporation of food data into the analyses.
Age-dependent changes in the inactivation of thyrotrophin-releasing hormone (TRH) were investigated in two subcellular fractions prepared from hypothalamus, thalamus, cortex and cerebellum of male rats. It was found that, in both supernatant and particulate fractions from the four brain areas, enzyme activity increased to a peak at 10–25 days of age and then decreased gradually until adult levels were reached. The changes in TRH degradation observed may be related to alterations in hypothalamic TRH content with age and to maturation of the tripeptide's putative neurotransmitter/neuromodulator function.
The subsequent two sentences are incorrect: “Although healthy subjects breathe spontaneously over a wide range of frequencies … 0.11 Hz is far below the average breathing frequencies of healthy subjects. Moreover, fully 70% of Cooper's subjects breathed at rates below ∼0.22–0.28 Hz ”. It is not abnormal to breath spontaneously at just below 13–17 breaths per minute (0.22–0.28 Hz) nor at 7 breaths per minute (0.1 Hz). The views expressed are those of the authors and not necessarily those of the National Health Service, the National Institute for Health Research or the Department of Health.
In many long-lived vertebrates (including humans), adult males have shorter lifespans than adult females, partly as a result of higher annual rates of mortality in males and partly owing to sex differences in the rate of ageing. A probable explanation of the evolution of sex differences in ageing is that, in polygynous species, intense intrasexual competition between males restricts the number of seasons for which individual males are able to breed successfully, weakening selection pressures favouring adult longevity in males relative to females. If this is the case, sex differences in adult longevity and in the onset and rate of senescence should be greater in polygynous species than in monogamous ones and their magnitude should be related to the duration of effective breeding males compared with females. Here, we use data from longitudinal studies of vertebrates to show that reduced longevity in adult males (relative to females) is commonly associated with a more rapid decline in male than female survival with increasing age and is largely confined to polygynous species. The magnitude of sex differences in adult longevity in different species is consistently related to the magnitude of sex differences in the duration of effective breeding, calculated across surviving adults. Our results are consistent with the suggestion that sex differences in senescence in polygynous species are a consequence of weaker selection for longevity in males than females.
