Areas Of Low Population Density Research Articles

Opportunistic screening for atrial fibrillation in a rural area.

Opportunistic screening is an effective means of identifying subjects with Atrial Fibrillation (AF). Previous studies of opportunistic screening have been performed areas with high population density and before the development of novel oral anticoagulant drugs. We performed a study to determine feasibility of AF screening in a predominantly rural, low population density area. Over 6 months, subjects 65 years and older were screened by local General Practitioners using radial pulse palpation confirmed by 12 lead Electrocardiogram. Data were recorded electronically and those with newly identified AF were followed up to examine management post diagnosis. In total, 7262 subjects were screened and an irregular pulse was found in 916 (12.6%) of whom 735 (10.1%) had known AF and 55 (0.76%) had newly detected AF. Of these 55 patients with newly documented AF, 28 (50.9%) were women, 38 (69.1%) had hypertension and eight (14.5%) had a smoking history. Mean body mass index in subjects with newly documented AF was 28.9 kg/m(2)(SD 5.6) There was no significant difference in gender mix (P = 0.4), smoking history (P = 0.8) or alcohol history (P = 0.8) with the overall population. Fifty-one (92.7%) subjects had a CHA2DS2VaSC score ≥ 2 of whom 33 (64.7%) were eventually anticoagulated and nine (17.6%) commenced on Aspirin. The rate of newly identified patients in AF was lower than in previous reported key studies because of a higher rate of subjects with known AF. Opportunistic AF screening in a rural environment identified a substantial number of new cases, although less than in previous screening studies.

Comparison of Constrained and Ad Hoc Demand-Responsive Transportation Systems

Planning public transport services for areas of low population density is important to enable travel by those without convenient travel options. In such areas, transit vehicles frequently travel with few passengers or even no passengers on board and thereby incur more cost to the transport providers. Demand-responsive transportation (DRT) services are potentially an efficient mobility solution to this problem. The choice of a DRT scheme is important because different types of schemes may produce different performances in the same area with the same demand. Although many DRT schemes have some constraints (for example, a fixed route or fixed time), these impose additional constraints on users who are already constrained, for example, by a lack of access to a car or limited times to undertake activities. Removing the fixed constraint on time leads to evaluating the performance of an ad hoc system. This paper investigates the change in performance of two DRT schemes—a fixed-time but flexible route scheme and a completely ad hoc scheme—by using the multiagent simulation tool, MATSIM, a large-scale agent-based transport simulation, and real data from an existing fixed-time DRT service in rural Victoria, Australia. Experimentation showed that the schemes produced different outcomes for the operator and passengers; however, the optimization algorithm was less important in areas of low demand. Higher levels of demand led to extensive vehicle travel for an ad hoc service, but altering the headways between fixed-time services could achieve a middle ground for operators and passengers. This work is a first step toward developing a decision support tool to evaluate DRT schemes, in particular for those integrated with other modes of transport.

Dynamics of the Thirteenth-century Depopulation of the Northern San Juan: The View from Cedar Mesa

Tree-ring dates and ceramic seriations are used to refine the chronology of Pueblo depopulation of the Cedar Mesa-Natural Bridges area of southeastern Utah. The early to mid-1200s saw increased occupation in the canyons, but mesa settings continue to be inhabited throughout as well. Wood-cutting for construction tapers off in the 1250s and ends in the 1260s, well before the onset of 1276–1299 “great drought.” Factors contributing to the depopulation are reviewed, including regional evidence for shorter growing seasons. Widespread warfare may have motivated people to leave areas of low population density, such as Cedar Mesa, to join the more secure large settlements that continued to grow in southwestern Colorado, even as overall population in that area began to decline.

Cassava brown streak disease and the sustainability of a clean seed system.

One method of reducing disease in crops is the dissemination of disease‐free planting material from a multiplication site to growers. This study assesses the validity and sustainability of this method for cassava brown streak disease, a threat to cassava crops across East Africa. Using mathematical modelling, the effects of different environmental and control conditions on pathogen spread were determined in a single‐field multiplication site. High disease pressure, through large vector populations and disease in the surrounding area, combined with poor roguing practice, resulted in unsuccessful disease suppression. However, fields may produce sufficiently clean material for replanting if these factors can be overcome. Assessing the sustainability of a low‐pressure system over multiple harvests, well‐managed fields were found to maintain low disease levels, although producing sufficient cuttings may prove challenging. Replanting fields from the previous harvest does not lead to degeneration of planting material, only cutting numbers, and the importation of new clean material is not necessarily required. It is recommended that multiplication sites are only established in areas of low disease pressure and vector population density, and the importance of training in field management is emphasized. Cultivars displaying strong foliar symptoms are to be encouraged, as these allow for effective roguing, resulting in negative selection against the disease and reducing its spread. Finally, efforts to increase plant multiplication rates, the number of cuttings that can be obtained from each plant, have a significant impact on the sustainability of sites, as this represents the primary limiting factor to success.

Evaluación de modelos geoestadísticos aplicados a la exposición al contaminante atmosférico PM10 en Chile

Se modela la exposición al contaminante atmosférico MP10 a partir de los datos registrados en 108 estaciones de monitoreo pertenecientes al Sistema Nacional de Calidad del Aire, utilizando geoestadística aplicada por medio del método Kriging ordinario, por su cualidad de representar fenómenos cuyos valores varían en función de la localización espacial de puntos de observación. El procedimiento se lleva a cabo en tres etapas: (1) Análisis exploratorio de los datos, para determinar si es necesario o no la transformación de los datos y la eliminación de tendencia en los mismos. (2) Análisis estructural para el cálculo del semivariograma experimental y el ajuste a seis modelos matemáticos teóricos seleccionados. (3) Predicciones para la obtención del Mapa predicción y mapa de errores estándar de la predicción.Los resultados obtenidos han permitido crear una superficie de valores estimados de exposición a PM10, que entre sus principales características, presenta una distribución territorial con un fuerte sesgo regional, concentrándose espacialmente en territorios del cluster minero y áreas metropolitanas. Los mayores errores de predicción se dan en sectores de baja densidad poblacional y de estaciones de monitoreo, en el desierto de Atacama y la cordillera de Los Andes.Revista Ciencias Espaciales, Volumen 8, Número 1 Primavera, 2015; 441-457

Bird biodiversity assessments in temperate forest: the value of point count versus acoustic monitoring protocols.

Effective monitoring programs for biodiversity are needed to assess trends in biodiversity and evaluate the consequences of management. This is particularly true for birds and faunas that occupy interior forest and other areas of low human population density, as these are frequently under-sampled compared to other habitats. For birds, Autonomous Recording Units (ARUs) have been proposed as a supplement or alternative to point counts made by human observers to enhance monitoring efforts. We employed two strategies (i.e., simultaneous-collection and same-season) to compare point count and ARU methods for quantifying species richness and composition of birds in temperate interior forests. The simultaneous-collection strategy compares surveys by ARUs and point counts, with methods matched in time, location, and survey duration such that the person and machine simultaneously collect data. The same-season strategy compares surveys from ARUs and point counts conducted at the same locations throughout the breeding season, but methods differ in the number, duration, and frequency of surveys. This second strategy more closely follows the ways in which monitoring programs are likely to be implemented. Site-specific estimates of richness (but not species composition) differed between methods; however, the nature of the relationship was dependent on the assessment strategy. Estimates of richness from point counts were greater than estimates from ARUs in the simultaneous-collection strategy. Woodpeckers in particular, were less frequently identified from ARUs than point counts with this strategy. Conversely, estimates of richness were lower from point counts than ARUs in the same-season strategy. Moreover, in the same-season strategy, ARUs detected the occurrence of passerines at a higher frequency than did point counts. Differences between ARU and point count methods were only detected in site-level comparisons. Importantly, both methods provide similar estimates of species richness and composition for the region. Consequently, if single visits to sites or short-term monitoring are the goal, point counts will likely perform better than ARUs, especially if species are rare or vocalize infrequently. However, if seasonal or annual monitoring of sites is the goal, ARUs offer a viable alternative to standard point-count methods, especially in the context of large-scale or long-term monitoring of temperate forest birds.

A Test of the New VIIRS Lights Data Set: Population and Economic Output in Africa

The present study analyses the new Visible Infrared Imaging Radiometer Suite (VIIRS) lights data to determine whether it can provide more accurate proxies for socioeconomic data in areas with poor quality data than proxies based on stable lights. Our analysis indicates that VIIRS lights are a promising supplementary source for standard measures on population and economic output at a small scale, especially for low population and economic density areas in Africa. The current analysis also suggests that in comparison to stable lights generated by the DMSP-OLS system, data generated by the VIIRS system provide more information to estimate population than output index. However, further analysis and formal statistical models are needed to evaluate the usefulness of VIIRS lights versus other lights products. With more advanced methods, there is also a potential to generate a synthetic index by combining different lights products to produce a better proxy measure for other indexes.

The Role of Geographic Factors in Human Papillomavirus (HPV) Vaccine Uptake Among Adolescent Girls in the United States

Abstract There has been limited research examining the role of geographic factors in human papillomavirus (HPV) vaccine uptake among adolescent girls. This study is one of the first to investigate and identify community-level geographic factors that may be associated with HPV vaccine uptake in the United States. We analyzed data from the 2011 and 2012 National Immunization Survey-Teen to examine associations of HPV vaccine initiation (receipt of at least one dose based on healthcare provider records) among female adolescents aged 13 to 17 years (N = 20,565) with ZIP code level geographic factors that were linked to the survey. Analyses were conducted using weighted logistic regression that included state-random effects. HPV vaccine initiation was approximately 53% in both 2011 and 2012. Racial composition and urban/rural residence were both independently associated with vaccine initiation (P = < 0.05). Initiation was higher among girls living in communities where the majority (>50%) of the population was Hispanic compared to communities where the majority of the population was non-Hispanic white (69.0% vs 49.9%; Adjusted Odds Ratio (AOR) 1.55, 95% CI, 1.33–1.80). Girls living in high population density areas (urban) had higher HPV vaccine initiation compared to those living in low population density areas (rural) (56% vs 44.6%; AOR 1.37, 95% CI, 1.13–1.65). Initiation was also higher among girls living in the most impoverished communities compared to girls living in the least impoverished communities (61% vs 50.4%), but community-level poverty was not significant in the adjusted analysis. Higher HPV vaccination coverage in poor urban communities with a high proportion of racial/ethnic minorities may be partly attributable to targeted interventions and the continued effectiveness of the Vaccines for Children program (VFC), which provides recommended vaccines at no cost to eligible children. Learning more about factors that influence higher HPV vaccination initiation rates among certain groups might inform intervention strategies for groups with lower initiation rates.

Rainfall and sentinel chicken seroconversions predict human cases of Murray Valley encephalitis in the north of Western Australia.

BackgroundMurray Valley encephalitis virus (MVEV) is a flavivirus that occurs in Australia and New Guinea. While clinical cases are uncommon, MVEV can cause severe encephalitis with high mortality. Sentinel chicken surveillance is used at many sites around Australia to provide an early warning system for risk of human infection in areas that have low population density and geographical remoteness. MVEV in Western Australia occurs in areas of low population density and geographical remoteness, resulting in logistical challenges with surveillance systems and few human cases. While epidemiological data has suggested an association between rainfall and MVEV activity in outbreak years, it has not been quantified, and the association between rainfall and sporadic cases is less clear. In this study we analysed 22 years of sentinel chicken and human case data from Western Australia in order to evaluate the effectiveness of sentinel chicken surveillance for MVEV and assess the association between rainfall and MVEV activity.MethodsSentinel chicken seroconversion, human case and rainfall data from the Kimberley and Pilbara regions of Western Australia from 1990 to 2011 were analysed using negative binomial regression. Sentinel chicken seroconversion and human cases were used as dependent variables in the model. The model was then tested against sentinel chicken and rainfall data from 2012 and 2013.ResultsSentinel chicken seroconversion preceded all human cases except two in March 1993. Rainfall in the prior three months was significantly associated with both sentinel chicken seroconversion and human cases across the regions of interest. Sentinel chicken seroconversion was also predictive of human cases in the models. The model predicted sentinel chicken seroconversion in the Kimberley but not in the Pilbara, where seroconversions early in 2012 were not predicted. The latter may be due to localised MVEV activity in isolated foci at dams, which do not reflect broader virus activity in the region.ConclusionsWe showed that rainfall and sentinel chickens provide a useful early warning of MVEV risk to humans across endemic and epidemic areas, and that a combination of the two indicators improves the ability to assess MVEV risk and inform risk management measures.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-014-0672-3) contains supplementary material, which is available to authorized users.

Optimizing energy for a ‘green’ vaccine supply chain

This paper describes an approach piloted in the Kasserine region of Tunisia to increase the energy efficiency of the distribution of vaccines and temperature sensitive drugs. The objectives of an approach, known as the ‘net zero energy’ (NZE) supply chain were demonstrated within the first year of operation. The existing distribution system was modified to store vaccines and medicines in the same buildings and to transport them according to pre-scheduled and optimized delivery circuits. Electric utility vehicles, dedicated to the integrated delivery of vaccines and medicines, improved the regularity and reliability of the supply chains. Solar energy, linked to the electricity grid at regional and district stores, supplied over 100% of consumption meeting all energy needs for storage, cooling and transportation. Significant benefits to the quality and costs of distribution were demonstrated. Supply trips were scheduled, integrated and reliable, energy consumption was reduced, the recurrent cost of electricity was eliminated and the release of carbon to the atmosphere was reduced. Although the initial capital cost of scaling up implementation of NZE remain high today, commercial forecasts predict cost reduction for solar energy and electric vehicles that may permit a step-wise implementation over the next 7–10 years.Efficiency in the use of energy and in the deployment of transport is already a critical component of distribution logistics in both private and public sectors of industrialized countries. The NZE approach has an intensified rationale in countries where energy costs threaten the maintenance of public health services in areas of low population density. In these countries where the mobility of health personnel and timely arrival of supplies is at risk, NZE has the potential to reduce energy costs and release recurrent budget to other needs of service delivery while also improving the supply chain.

Mapping a new future: using spatial multiple criteria analysis to identify novel habitats for assisted colonization of endangered species

AbstractMany species with restricted ranges or poor dispersal ability will occupy suboptimal habitats under climate change. The practice of translocating populations to more suitable areas outside the known historical range (assisted colonization) has been advanced as a solution to reduce the risk of extinction in the wild. Due to the high‐risk and bureaucratic complexities of assisted colonization, it is imperative that a systematic process is used to select release sites that have a reduced likelihood of translocation failure. Here we demonstrate how a spatially explicit, three‐stage multiple criteria analysis (MCA) can be used to identify potentially suitable sites for assisted colonization of an endangered species. We employ this method as an initial screening process, prior to final selection of sites for assisted colonization of the critically endangered western swamp tortoise (Pseudemydura umbrina). This species occurs naturally in two small reserves in southwestern Australia, and is currently threatened by a shift to a drier climate and consequent changes to hydrological regimes. A literature review, characteristics of remnant P. umbrina habitat, and expert knowledge were used to create a composite index of habitat suitability, mapped across the entire south‐west bioregion of Australia. The most suitable sites were 150 to 250 km south of the known range of P. umbrina, in areas of high landscape connectivity and low human population density. A subset of sites were examined in further detail and ranked using weighted summation. Careful use of MCA, taking into account data uncertainties and differences in expert opinion, can be a valuable tool when evaluating novel habitats for threatened species.

Addressing population heterogeneity and distribution in epidemics models using a cellular automata approach.

BackgroundThe spread of an infectious disease is determined by biological and social factors. Models based on cellular automata are adequate to describe such natural systems consisting of a massive collection of simple interacting objects. They characterize the time evolution of the global system as the emergent behaviour resulting from the interaction of the objects, whose behaviour is defined through a set of simple rules that encode the individual behaviour and the transmission dynamic.MethodsAn epidemic is characterized trough an individual–based–model built upon cellular automata. In the proposed model, each individual of the population is represented by a cell of the automata. This way of modeling an epidemic situation allows to individually define the characteristic of each individual, establish different scenarios and implement control strategies.ResultsA cellular automata model to study the time evolution of a heterogeneous populations through the various stages of disease was proposed, allowing the inclusion of individual heterogeneity, geographical characteristics and social factors that determine the dynamic of the desease. Different assumptions made to built the classical model were evaluated, leading to following results: i) for low contact rate (like in quarantine process or low density population areas) the number of infective individuals is lower than other areas where the contact rate is higher, and ii) for different initial spacial distributions of infected individuals different epidemic dynamics are obtained due to its influence on the transition rate and the reproductive ratio of disease.ConclusionsThe contact rate and spatial distributions have a central role in the spread of a disease. For low density populations the spread is very low and the number of infected individuals is lower than in highly populated areas. The spacial distribution of the population and the disease focus as well as the geographical characteristic of the area play a central role in the dynamics of the desease.

Pre-test Data and Lessons Learned from a Group Research Project Examining Changes in Physical Activity Behavior Following Construction of a Rails-to-Trails Facility

Built environments in rural settings may provide greater challenges than those in urban settings due to physical characteristics inherent to low-density population areas. Multiuse recreational trails, such as those that repurpose abandoned railroad lines, may provide a physical activity resource that is well suited to rural areas. However, the direct impact of trail availability on physical activity behavior is not generally known because it is unclear whether activity reported in most trail research represents increases in physical activity or displacement of activity in individuals who previously exercised in other locations. This research, initiated by a group of students in a graduate seminar, represents to our knowledge, the first instance in which PA was assessed prior to the availability of an entirely new rails-to-trails facility. The research was implemented using a nonequivalent dependent variable design to counter the lack of a control group; the nonequivalent dependent variable chosen was weekly servings of fruit and vegetables. Participants responding to intercept interviews classified days of activity during the prior week as mild, moderate or vigorous. Baseline results for 244 participants suggested generally low levels of activity prior to trail availability; number of reported days of activity decreased with described intensity. We also discuss several issues encountered in planning and implementing this group project including those related to data collection, variable levels of commitment among student members, and inconsistent project management, and offer potential solutions to these concerns.

Agricultural Commercialization, Land Expansion, and Homegrown Large-Scale Farmers: Insights from Ghana

The past decade has seen several African countries increasing their agricultural growth, a trend largely underpinned by increases in land area cultivated instead of productivity increases. Meanwhile, scholars debate whether Africa should pursue a strategy of large-scale or smallholder farms, paying little attention to a special group of smallholder farmers who have transitioned to become medium- and large-scale farmers. This study, therefore, begins to analyze this group of farmers, using qualitative data from in-depth interviews and focus group discussions in Ghana. We analyze their characteristics, ingredients of farm-size expansion, and commercialization. Numerous insights are gained and hypotheses formulated for future research. One important insight is that with the right attitude, exposure, and discipline, it is possible for smallholder farmers to increase their farm size and commercialize regardless of initial farm enterprise choice. However, to transition, initial farm size and farming system appear critical, with farmers in areas of low population density and flat topography more likely to acquire larger farming land. The transition, however, occurs gradually over 20 to 30 years, with mean annual land acquisition rates ranging from 0.3 to 24.3 acres per year. In the transition process, large- and medium-scale farmers are found to increase their use of modern farm inputs (such as fertilizer and high-yielding seed varieties) and agricultural technologies (such as tractors and processing machinery) and appear more productive than smallholder farmers. Additional quantitative analyses using representative survey data are, however, needed to substantiate the observed qualitative patterns and to further understand the trajectories of farm size expansion and the implications for agricultural productivity and commercialization.

Residence place as a risk factor in different types of fatal car accidents

The association between place of residence, population density, relief and type of event (collision or non-collision of the vehicle) has not been evaluated in developing countries. The main objective of this study is to determine the differential factors associated with the occurrence of deaths of collision and non-collision automobile users in Patagonia, Argentina. A multiple logistic regression analysis was performed using as the dependent variable death by car accident (collision or non-collision of the vehicle) and sex, age, place of residence of the victim, relief and population density as the independent variables. Collision fatalities were related to areas of high population density, while non-collision fatalities were related to areas of low population density, mountainous landscape and place of residence of the victims outside the Patagonian region. The results obtained in this study indicate the need to develop differential primary prevention policies by place of residence of car occupants, focusing on Patagonia non-resident drivers and by emphasising non-collision accidents.

Effluent Storage and Biomat Occurrence among Septic System Absorption Field Architectures in a Typic Fragiudult

On-site wastewater treatment systems (OWTSs) are commonly used by households in areas of low population density to treat household wastewater and recycle it back to the environment. However, new absorption field products of differing architecture types have recently become available. A 3-yr field study was conducted in Bethel Heights, northwest Arkansas to assess several newer architecture types (i.e., chambers, polystyrene-aggregate, and gravel-less pipe) relative to the traditional pipe-and-gravel design under wet- and dry-soil conditions. Thirteen products of four different architecture types were installed in 46-cm-deep trenches in a Captina silt loam (fine-silty, siliceous, active, mesic Typic Fragiudult). Products were evaluated based on in-trench solution storage measured with an electronic water-level sensor approximately weekly from January 2009 through January 2012. Between May 2010 and January 2012, the thickness of any biomat formation was measured approximately weekly by insertion of a wooden dowel through in-trench monitoring ports. Architecture type alone did not affect ( > 0.05) in-trench solution storage. However, solution storage among individual products differed under wet- and dry-soil conditions ( < 0.05). When present, biomat thickness differed significantly ( < 0.05) among all four architecture types, ranging from 1.4 to 6.2 cm thick on average in the pipe-and-aggregate and polystyrene-aggregate types, respectively. Regression analyses showed that biomat thickness increased in three products, did not change in nine products, and decreased in one product over time. Results showed that several currently approved alternative products had similar in-trench solution storage but that several alternative products also had greater solution storage than that of the traditional pipe-and-gravel system. With no observed effluent surfacing, the soil morphology approach appears to be adequate and appropriately environmentally conservative for assigning typical single-family loading rates to alternative OWTS products and to the traditional pipe-and-gravel system.

Spatial targeting of land rehabilitation: a relational analysis of cropland productivity decline in arid Uzbekistan

Irrigated croplands of Central Asia are highly prone to land degradation due to their fragile physical settings and extensive agricultural land use. Current remote-sensing data and spatio-temporal analyses allow for detecting regional trends in a land decline and for relating them to underlying factors which is important for developing mitigation strategies. This study aimed to (1) assess the cropland’s state in the large irrigated agricultural areas in the northern Uzbekistan based on the time series of MODIS NDVI images, (2) relate the degradation trend to its factors including soil quality, terrain, population density and land use, and (3) synthesize the results to provide recommendation on spatial targeting of land rehabilitation measures. An NDVI-based land degradation assessment revealed a significant decline of land productivity across 23.13% (94834.90 ha) of the arable area in the study region. The degraded cropland, located in the areas of high population pressure and characterized by better-quality soils, should be prioritized for rehabilitation measures. For the degraded cropland, found on the poor-quality soils and in the areas of low population density, depending on the severity of degradation, a decision has to be made whether to vacant the land from agriculture or to continue cultivation if the latter is an economically viable option.

비용 효율적 커버리지 확장을 위한 IEEE 802.16j 모바일 멀티-홉 릴레이 시스템

To complete the anywhere mobile service there should not be shaded areas. However, it is never economical to deploy BS`s (Base Stations) in a low population density area due to the low resource utilization. We propose a design technique to install RS`s(Relay Stations) which are cheaper than BS`s and find the condition in which the proposed technique is acceptible. The proposed design technique aims to allocate the frequency and time resources to RS`s to minimize the transmission rate degradation due to interferences between RS`s as well as to maximize the parallelism in transmission. We showed by simulation that the proposed technique achieves cost benefits when the expected traffic is less than 20.32 percent of the total BS capacity. The proposed technique is compatible with the IEEE 802.16j, thus can be extended to multi-hop configuration.

Effect of absorber coating on the performance of a solar still in the region of Ouargla (Algeria)

As the world’s population grows in number and riches, the demands for water and energy are increasing faster than ever. Reports on the availability of potable water have listed Algeria among top countries affected by water shortage. This work provides a study dealing with distillation for isolated low-density population areas using solar energy. The utmost objective of the present investigation is to enhance the yield of a solar still by improving the performance of its absorber. This was achieved by laminating the surface of the absorber by layers of treated alluvial sand. Small-scale solar-powered distillation pilot units have been set up and operated. The tests were conducted in Ouargla, south of Algeria. Two series of experiments were performed. The first consisted of studying the effect of the sand diameter on the daily output of the still. The influence of the sand surface density was investigated in the second series. The experimental results showed that: For a fixed mass of sand (given surface density), the yield improvement of the still was inversely proportional to the sand particle diameters. The output in distilled water for a fixed particle diameter increases with the increase in the sand surface density.

Reproductive dynamics of the sea urchin Paracentrotus lividus on the Galicia coast (NW Spain): effects of habitat and population density

We studied the spatial variability in the size at first maturity and the reproductive cycle of Paracentrotus lividus in Galicia, contributing key information for the exploitation and management of this resource. The size at maturity varied between 20.4 (±1.2 SE) mm and 27.9 ± 1.2 mm and was smaller in areas of low population density where sea urchins do not form patches. Using a nonlinear model, we analysed the effect of depth, body size, sex and population density on the temporal pattern of the gonad index. The maximum and minimum indices were obtained at 4 m depth in the months before and after the spring spawning, respectively. The depth also affected the cycle phase, and the sea urchins at 4 m depth spawned 9.4 ± 3.0 days later than the sea urchins at 8 m depth and 20.5 ± 3.0 days later than those at 12 m depth. Moreover, the sea urchins living in patches showed a slight increase in gonad size as a consequence of the better-quality habitat. This shows that there is no intraspecific competition in this area despite the high population densities reached (18.5 kg m−2).