Coupled trophic interactions with specialist predators or resources are thought to be primarily responsible for generating delayed density dependence. Previous theoretical studies suggest that autocorrelation in exogenous factors could generate apparent negative delayed density dependence in populations regulated only by direct density dependence. Using both linear and nonlinear models, we show that autocorrelated exogenous factors can generate the spurious appearance of not only negative, but also positive, delayed density dependence in populations regulated only by direct density dependence. Evidence for negative delayed density dependence is found mainly in populations exhibiting monotonic deterministic stability, whereas evidence for positive delayed density dependence is found mainly in populations exhibiting damped or persistent two-point cycles, or more complex deterministic dynamics. We argue that fluctuating resources (e.g., mast seeding) in bottom-up controlled communities could qualify as autocorrelated exogenous factors and cause apparent delayed density dependence in the population of their consumers.

ObjectiveTo conduct an analysis of the frequency of unhealthy food advertising on mainland Chinese television (TV) and children and adolescents’ risk of exposure to them.MethodsThe frequencies of all types of advertisements (ads) on forty TV channels in mainland China, the exact ad broadcast times, and the name and brand of all snacks and western fast foods advertised were recorded from 0800 hours to 2400 hours on both a weekday and a weekend day in a week. The difference in the frequencies of the diverse types of ads over eight time intervals (each time interval was 2 hours) were compared, and the trends in ad frequencies during the time intervals were described.ResultsThe TV channels broadcast 155 (91-183) (expressed as median [P 25-P 75]) food ads, 87 (38-123) snack ads, 49 (11-85) beverage ads, and 58 (25-76) ads of snacks suitable for limited consumption (SSLCs) in a day. The proportion of snack ads among food ads (SPF%) was 55.5% (40.3%-71.0%), and the proportion of SSLC ads among snack ads (LPS%) was 67.4% (55.4%-79.3%). The ad frequencies for food, snacks, SSLCs, and beverages demonstrated significant differences among the eight time intervals (all P=0.000). TV channels broadcast the most frequent ads for food, snacks, SSLCs, and beverages during the time interval from 2000 hours to 2200 hours among the eight time intervals.ConclusionsChinese children and adolescents may be at a high risk of exposure to unhealthy food advertising on TV. Reducing the exposure risk strongly requires multisectoral cooperation.

Objectives: Compared with Western countries, the incidence rates for breast cancer in China are still low. However, breast cancer appears to be hitting Chinese women at a much younger age, with a peak between 40 and 50 years. Furthermore, breast tumors of Asian women have molecular and genetic characteristics that are different from those of Caucasian women. Methods: A community-based study was designed to evaluate the relationship between lifestyles and breast cancer risk in Chinese women residing in Guangzhou. 16,314 subjects completed the questionnaire. Potential confounding factors included sociodemographic characteristics. Results: 33 individuals reported a history of breast cancer, yielding a prevalence rate of 202.3/100000. Associations between subjects' demographic and breast cancer risk factors were assessed. Breast cancer is associated with family history of breast cancer, X-rays received, benign breast disease and hyperlipoidemia or hypercholesteremia with elevated odds ratios. Conclusions: Family history of breast cancer, X-ray received benign breast disease and hyperlipoidemia or hypercholesteremia were significantly associated with risk of breast cancer and may havepotential for breast cancer risk assessment.

Previous work suggests that red environmental noise can lead to the spurious appearance of delayed density dependence (DDD) in unstructured populations regulated only by direct density dependence. We analysed the effect of noise reddening on the pattern of spurious DDD in several variants of the density-dependent age-structured population model. We found patterns of spurious DDD in structured populations with either density-dependent fertility or density-dependent survival of the first age class, inconsistent with predictions from unstructured population models. Moreover, we found that nonspurious negative DDD always emerges in populations with deterministic chaotic dynamics, regardless of population structure or the type of environmental noise. The effect of noise reddening in generating spurious DDD is often negligible in the chaotic region of population deterministic dynamics. Our findings suggest that differences in species' life histories may exhibit different patterns of spurious DDD (owing to noise reddening) than predicted by unstructured models.