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High Density Populations (high + density_population)
Selected AbstractsPlant spatial arrangement affects projected invasion speeds of two invasive thistlesOIKOS, Issue 9 2010Katherine M. Marchetto The spatial arrangement of plants in a landscape influences wind flow, but the extent that differences in the density of conspecifics and the height of surrounding vegetation influence population spread rates of wind dispersed plants is unknown. Wind speeds were measured at the capitulum level in conspecific arrays of different sizes and densities in high and low surrounding vegetation to determine how these factors affect wind speeds and therefore population spread rates of two invasive thistle species of economic importance, Carduus acanthoides and C. nutans. Only the largest and highest density array reduced wind speeds at a central focal thistle plant. The heights of capitula and surrounding vegetation also had significant effects on wind speed. When population spread rates were projected using integrodifference equations coupling previously published demography data with WALD wind dispersal models, large differences in spread rates resulted from differences in average horizontal wind speeds at capitulum height caused by conspecific density and surrounding vegetation height. This result highlights the importance of spatial structure for the calculation of accurate spread rates. The management implication is that if a manager has time to remove a limited number of thistle plants, an isolated thistle growing in low surrounding vegetation should be targeted rather than a similar sized thistle in a high density population with high surrounding vegetation, if the objective is to reduce spread rates. [source] Seasonal monogamy and multiple paternity in a wild population of a territorial reptile (tuatara)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009JENNIFER A. MOORE Investigating the mating system of a population provides insight into the evolution of reproductive patterns, and can inform conservation management of threatened or endangered species. Combining behavioural and genetic data is necessary to fully understand the mating system and factors affecting male reproductive success, yet behavioural data are often difficult to collect for threatened species. In the present study, we use behavioural data and paternity analyses to characterize the mating system of a high density population of a long-lived, ancient reptile (tuatara, Sphenodon punctatus). We further investigate the phenotypic traits (including body size, body condition, tail length, and ectoparasite load) that affect male reproductive success. Our behavioural data reflect a seasonally monogamous system with low levels of polyandry and polygyny that are consistent with male mate guarding. Male reproduction is highly skewed (only 25,30% of males are successful), and body size is the primary predictor of male reproductive success. Based on the genetic data, multiple paternity was found in only 8% of clutches, and the results of the paternity analyses showed monandrous clutches from socially polyandrous females. Our behavioural and genetic results revealed complexities in female mating patterns that support the potential for cryptic female choice or sperm competition. This warrants further experimental investigation into the mechanisms underlying reptile fertilization and the disparities between social and genetic polyandry in wild populations. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 161,170. [source] Density-dependent mortality is mediated by foraging activity for prey fish in whole-lake experimentsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2003Peter A. Biro Summary 1Whereas the effects of density-dependent growth and survival on population dynamics are well-known, mechanisms that give rise to density dependence in animal populations are not well understood. We tested the hypothesis that the trade-off between growth and mortality rates is mediated by foraging activity and habitat use. Thus, if depletion of food by prey is density-dependent, and leads to greater foraging activity and risky habitat use, then visibility and encounter rates with predators must also increase. 2We tested this hypothesis by experimentally manipulating the density of young rainbow trout (Oncorhynchus mykiss) at risk of cannibalism, in a replicated single-factor experiment using eight small lakes, during an entire growing season. 3We found no evidence for density-dependent depletion of daphnid food in the nearshore refuge where most age-0 trout resided. Nonetheless, the proportion of time spent moving by individual age-0 trout, the proportion of individuals continuously active, and use of deeper habitats was greater in high density populations than in low density populations. Differences in food abundance among lakes had no effect on measures of activity or habitat use. 4Mortality of age-0 trout over the growing season was higher in high density populations, and in lakes with lower daphnid food abundance. Therefore, population-level mortality of age-0 trout is linked to greater activity and use of risky habitats by individuals at high densities. We suspect that food resources were depleted at small spatial and temporal scales not detected by our plankton sampling in the high density treatment, because food-dependent activity and habitat use by age-0 trout occurs in our lakes when food abundance is experimentally manipulated (Biro, Post & Parkinson, in press). [source] Efficacy of trap and lure types for detection of Agrilus planipennis (Col., Buprestidae) at low densityJOURNAL OF APPLIED ENTOMOLOGY, Issue 4 2010J. M. Marshall Abstract Development of effective trapping tools for forest pests and evaluating the key components of these tools is necessary to locate early-stage infestations and develop management responses to them. Agrilus planipennis Fairmaire (emerald ash borer) is an introduced pest of ash (Fraxinus spp. L.) in North America. The effectiveness of different trap and lure combinations were tested in areas with low and high density populations of A. planipennis. At low density sites, purple prism traps outperformed green traps and girdled ash trap trees in capture rates (adults per day) and rates of detection of A. planipennis. Also, manuka oil lures, used as a standard lure in a national survey programme, captured higher rates of A. planipennis than did previous standards of girdled ash trap trees. There was no logistic relationship between the detection of A. planipennis on a trap and the diameter of the ash tree from which the trap was suspended, possibly because of the use of artificial lures with these traps. There was also no difference in the mean number of A. lanipennis captured per day between ash species and between vigour rating of ash associated with the traps. However, traps placed in open grown and dominant trees captured more beetles than traps placed in lower canopy class trees. At sites defined as low and high density, there was no difference in the larval density per cm3 of phloem. This suggests that exposure time to A. planipennis has been shorter at those low density sites. By exploiting the trap and tree characteristics that improve A. planipennis capture rates and detection efficacy, there can be future improvement in management of this pest. If detection can occur before infested ash trees exhibit signs and symptoms, there may be a potential for reducing the mortality of ash within stands. [source] Use of historical temperature data for timing insecticide applications of the Nantucket pine tip moth (Lepidoptera: Tortricidae): evaluation of damage and volume increment efficacyAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2002Christopher J. Fettig Abstract 1,The effectiveness of optimal spray period intervals based on mean daily temperatures were evaluated as a spray-timing tool to control high density populations of the Nantucket pine tip moth Rhyacionia frustrana (Comstock). 2,Initial tree growth realized from first generation R. frustrana control was compared to that from conventional applications of one insecticide treatment scheduled for each of three annual generations. 3,The optimal spray period intervals provided by Fettig et al. (2000a) were highly effective for controlling R. frustrana infestations. The control group averaged 47.0 ± 2.2% whole tree damage for all sites and generations as compared to 0.6 ± 0.2% for the treated group. 4,Volume gains attributable to R. frustrana control averaged 16.9%, 46.4% and 98.6% for first generation control, and 46.6%, 72.7% and 146.3% for conventional applications of one insecticide treatment scheduled for each of three annual R. frustrana generations at Northampton, Halifax I and Halifax II, respectively. Growth returns increased as mean damage estimates increased for both treatments, suggesting that returns realized from a single, first generation application are likely to increase with population density. [source] Reproductive Allocation Patterns in Different Density Populations of Spring WheatJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2008Jing Liu Abstract The effects of increased intraspecific competition on size hierarchies (size inequality) and reproductive allocation were investigated in populations of the annual plant, spring wheat (Triticum aestivum). A series of densities (100, 300, 1 000, 3 000 and 10 000 plants/m2) along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient (R2 = 0.927), which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition (100 plants/m2), individual reproductive allocation was size independent but, in high density populations (300, 1 000, 3 000 and 10 000 plants/m2), where competition occurred, individual reproductive allocation was size dependent: the small proportion of larger individuals were winners in competition and got higher reproductive allocation (lower marginal reproductive allocation; MRA), and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation (higher MRA). In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation (with a negative relationship between them). However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies. [source] Shifts in breeding habitat selection behaviour in response to population densityOIKOS, Issue 7 2010Ché M. Elkin We tested whether mountain pine beetles Dendroctonus ponderosae, an insect herbivore that exhibits outbreak population dynamics, modifies its habitat selection behaviour in response to density-dependent environmental shifts. Using an individual-based habitat selection model, we formulated predictions of how beetle population density will influence breeding habitat selectivity. Our model predicted that beetles should be more selective at intermediate densities than at low or high densities. The mechanisms influencing optimal selectivity differed between low and high density populations. In low density populations, breeding site availability was the primary factor affecting selectivity, whereas intraspecific competition and the reliability of habitat quality cues were important in high density populations. We tested our model predictions in natural populations that encompassed a range of beetle population densities. Our empirical findings supported the two key predictions from our model. First, habitat quality was more variable in high density populations. Second, individuals in high density populations were less selective compared to beetles from intermediate density populations. Our results demonstrate that beetles alter their habitat selection behaviour in response to density-dependent shifts. We propose that the behavioural changes we identified may influence the rate at which beetle populations transition between density states. [source] | ||||||||||