Spatial Distribution Of Individuals Research Articles

Evaluation of Strategies to Enhance Community-Based Naloxone Distribution Supported by an Opioid Settlement

Many US states are substantially increasing community-based naloxone distribution, supported in part through settlements from opioid manufacturers and distributors. To evaluate the potential impact of increased naloxone availability on opioid overdose deaths (OODs) and explore strategies to enhance this impact by integrating interventions to address solitary drug use. This decision analytical modeling study used PROFOUND (Prevention and Rescue of Fentanyl and Other Opioid Overdoses Using Optimized Naloxone Distribution Strategies), a previously published simulation model, to forecast annual OODs between January 2023 and December 2025. The simulated study population included individuals from Rhode Island who misused opioids and stimulants and were at risk for opioid overdose. The study modeled expanded naloxone distribution supported by the state's opioid settlement (50 000 naloxone nasal spray kits each year). Two approaches to expanding naloxone distribution were evaluated: one based on historical spatial patterns of naloxone distribution (supply-based approach) and one based on the spatial distribution of individuals at risk (demand-based approach). In addition, hypothetical interventions to enhance the likelihood of witnessed overdoses in private or semiprivate settings were considered. Annual number of OODs and ratio of fatal to nonfatal opioid overdoses. Modeling results indicated that distributing more naloxone supported by the state's opioid settlement could reduce OODs by 6.3% (95% simulation interval [SI], 0.3%-13.7%) and 8.8% (95% SI, 1.8%-17.5%) in 2025 with the supply-based and demand-based approaches, respectively. However, increasing witnessed overdoses by 20% to 60% demonstrated greater potential for reducing OODs, ranging from 8.5% (95% SI, 0.0%-20.3%) to 24.1% (95% SI, 8.6%-39.3%). Notably, synergistic associations were observed when combining both interventions: increased naloxone distribution with the 2 approaches and a 60% increase in witnessed overdoses could reduce OODs in 2025 by 33.5% (95% SI, 17.1%-50.4%) and 37.4% (95% SI, 19.6%-56.3%), respectively. These findings suggest that interventions to address solitary drug use are needed to maximize the impact of continued efforts to increase community-based naloxone distribution, which may be particularly important for jurisdictions that have strong community-based naloxone distribution programs.

Disturbance Level Mediates the Differential Resistance of Tropical Dry Forest Soil and Vegetation Attributes to High-Intensity Hurricanes

Hurricanes are extreme climatic events frequently affecting tropical regions such as the tropical dry forests (TDFs) in Mexico, where its frequency/intensity is expected to increase toward the year 2100. To answer how resistant is a Mexican tropical dry forest to a high-intensity hurricane, and if its degree of resistance was mediated by its conservation degree, we evaluated the effect of a category 4 hurricane over the tree community, soil nutrients, and soil enzymatic activity in two contrasting TDF ecosystems: Old-Growth Forest (OGF) and Secondary Forest (SF). In general, vegetation richness and diversity showed very high resistance one year after the hurricane, but several structural attributes did not, especially in the OGF where the tree mortality related to vegetation structure and spatial distribution of individuals was higher. Then, in the short term, SF vegetation appeared to be more resistant, whereas the OGF, with more biomass to lose, appeared to be more vulnerable. Conversely, most soil attributes showed low resistance in both stages, but especially in SF which could face more severe nutrient limitations. The response of TDF to high-intensity hurricanes, in terms of above- and belowground processes, was in part dependent on its disturbance level. Moreover, an increase in the intensity/frequency of hurricanes could lead this TDF toward a high nutrient limitation (especially by phosphorus) for the plants and consequently toward a loss of soil functioning, especially in the SF. This eventually could produce a severe degradation in fundamental attributes and functions of the ecosystem.

An Individual-Based Spatial Epidemiological Model for the Spread of Plant Diseases

AbstractIn the study of plant disease epidemics, the state of each individual in the population and their spatial location should be considered when modeling disease spread. We present a model to describe the spread of plant diseases, where the infection of a susceptible individual depends on the transmission rate of infected individuals and the spatial correlation. This latter is introduced through the Matérn correlation function, accounting for spatial dependence based on distance. Almond leaf scorch disease, caused by the bacterium Xylella fastidiosa, was used as a case study to test the behavior of the model parameters and the variability due to the characteristics and location of initial disease introduction using a proposed simulation algorithm. The greatest variability in the results depended on the range parameter of the Matérn correlation, i.e., the distance at which two observations can be considered spatially uncorrelated, and the initial introduction. The spatial distribution of individuals also had a strong influence on disease spread, highlighting that areas without trees acted as barriers when their extent was greater than the range parameter. It should be stressed that this individual-based model can be applied to other plant diseases, adapting the parameter values to their particular epidemiological characteristics.

The behavior of population dispersion employing various numerical techniques

The exploration of population diversity motivated us to present this paper. A mathematical model for the ecological process of population dispersion is finally considered by us to figure out the dispersion of population along the area. The dispersal from one's home site to the next is considered the most important phenomenon in the demographic and evolutionary dynamics of the population. The most important factor regarding dispersal is the spatial distribution of individuals. This dispersal may result in enhanced clamping, huge randomness, or even more spacing. The Adomian Decomposition method has opted to work out the problem analytically. Numerical schemes brought an approximate solution by incorporating the Forward-in-Time and Central-In-Space (FTCS) scheme, the Crank Nicolson (CN) scheme, and Numerov’s method. The validity and efficiency of schemes employed for the proposed model are supported by core properties like stability, consistency, and convergence. A comparison is made between the results calculated via schemes and the one analytically.

Populations structure and role of Hedysarum grandiflorum in the spatial organization of plant communities of petrophyte steppes

Comprehensive monitoring and assessment of the state of vegetation cover of Samara Trans-Volga show that steppe landscapes are the most vulnerable, and areas of petrophytic steppes. Rare species include Hedysarum grandiflorum Pall. This species is protected in the territory of Russia. Structural features of cenopopopulations were studied in more than 50 natural-territorial complexes. The number of individuals in populations of specific locations is usually sufficient to make a comprehensive assessment of the species at different levels of organization (organismal, population, species, and phytocoenotic). The study of cenopopopulations was carried out in 1998-2020. During the field studies, we used the method of laying test sites (stationary plots). Data on the spatial distribution of individuals were processed in the R environment (version 3.3.2) using the SPATSTAT package. The intensity of the location of individuals of the studied species was estimated using the Gaussian kernel function with boundary correction. Most of the H. grandiflorum populations known to us are (or have already been) degraded or even critical due to irrational economic exploitation of natural complexes. The random type of placement of individuals indicates favorable habitat conditions for the studied species at stationary plots. Perhaps, some tendency of pregenerative individuals to cluster is due to the mosaic location of sites suitable for seed germination (small depressions with sufficient moisture, areas not occupied by vegetation, formed under the action of exogenous factors).

High degree of individual repeatability found in the annual migrations of walleye (Sander vitreus) in eastern Lake Ontario

Adult walleye (Sander vitreus) conduct annual migrations from riverine spawning sites in the Bay of Quinte into the eastern basin of Lake Ontario to forage. Although fidelity to spawning river is quite high for these fish across the Laurentian Great Lakes, very little is known about the repeatability of site selection along the entirety of their annual migration. This study used multiple years of acoustic telemetry (2018–2020) to assess the within-individual repeatability of the timing associated with major migratory events (spawning river entry and departure, main lake entry and departure), as well as the average monthly spatial distribution of individuals throughout the year. Fine-scale sequence analysis was used to combine these two metrics to assess the within and among individual sequence dissimilarity in the population. Within-individual repeatability was high across most timing and spatial measures, and the sequence dissimilarity within individual sequences was significantly less than that among individuals. Sex and size were not significantly related to sequence dissimilarity, while individuals from the Trent River displayed more dissimilarity than those from the Napanee River. The high level of within-individual annual repeatability in migrations was demonstrated not only during spawning activity, but at a daily level throughout the entire year. This research shows that walleye possess the ability to orient themselves and navigate across long distances in a highly repeatable manner at all times of the year. Future work will be required to better understand the underlying mechanisms and drivers behind these abilities.

When complex movement yields simple dispersal: behavioural heterogeneity, spatial spread and parasitism in groups of micro-wasps

BackgroundUnderstanding how behavioural dynamics, inter-individual variability and individual interactions scale-up to shape the spatial spread and dispersal of animal populations is a major challenge in ecology. For biocontrol agents, such as the microscopic Trichogramma parasitic wasps, an understanding of movement strategies is also critical to predict pest-suppression performance in the field.MethodsWe experimentally studied the spatial propagation of groups of parasitoids and their patterns of parasitism. We investigated whether population spread is density-dependent, how it is affected by the presence of hosts, and whether the spatial distribution of parasitism (dispersal kernel) can be predicted from the observed spread of individuals. Using a novel experimental device and high-throughput imaging techniques, we continuously tracked the spatial spread of groups of parasitoids over large temporal and spatial scales (8 h; and 6 m, ca. 12,000 body lengths). We could thus study how population density, the presence of hosts and their spatial distribution impacted the rate of population spread, the spatial distribution of individuals during population expansion, the overall rate of parasitism and the dispersal kernel (position of parasitism events).ResultsHigher population density accelerated population spread, but only transiently: the rate of spread reverted to low values after 4 h, in a “tortoise-hare” effect. Interestingly, the presence of hosts suppressed this transiency and permitted a sustained high rate of population spread. Importantly, we found that population spread did not obey classical diffusion, but involved dynamical switches between resident and explorer movement modes. Population distribution was therefore not Gaussian, though surprisingly the distribution of parasitism (dispersal kernel) was.ConclusionsEven homogenous asexual groups of insects develop behavioural heterogeneities over a few hours, and the latter control patterns of population spread. Behavioural switching between resident and explorer states determined population distribution, density-dependence and dispersal. A simple Gaussian dispersal kernel did not reflect classical diffusion, but rather the interplay of several non-linearities at individual level. These results highlight the need to take into account behaviour and inter-individual heterogeneity to understand population spread in animals.

Density Estimation in Terrestrial Chelonian Populations Using Spatial Capture–Recapture and Search–Encounter Surveys

Having an accurate estimate of population size and density is imperative to the conservation of chelonian species and a central objective of many monitoring programs. Capture–recapture and related methods are widely used to obtain information about population size of chelonians. However, classical capture–recapture methods have strict spatial sampling requirements and do not account for lack of geographic closure caused by movement of individuals in and out of the surveyed landscape. Newly developed spatial capture–recapture (SCR) models address these limitations by specification of explicit models for spatial sampling as well as the spatial distribution of individuals in the population. Spatial capture–recapture models have not yet been applied to the study of chelonian populations. Here we demonstrate their application to a population of box turtles in Maryland that has been studied for 75 yr. Results support dramatic declines in population size of box turtles since the 1940s.

Gene-environment interactions explain a substantial portion of variability of common neuropsychiatric disorders

SummaryIn complex diseases, the phenotypic variability can be explained by genetic variation (G), environmental stimuli (E), and interaction of genetic and environmental factors (G-by-E effects), among which the contribution G-by-E remains largely unknown. In this study, we focus on ten major neuropsychiatric disorders using data for 138,383 United States families with 404,475 unique individuals. We show that, while gene-environment interactions account for only a small portion of the total phenotypic variance for a subset of disorders (depression, adjustment disorder, substance abuse), they explain a rather large portion of the phenotypic variation of the remaining disorders: over 20% for migraine and close to or over 30% for anxiety/phobic disorder, attention-deficit/hyperactivity disorder, recurrent headaches, sleep disorders, and post-traumatic stress disorder. In this study, we have incorporated—in the same analysis—clinical data, family pedigrees, the spatial distribution of individuals, their socioeconomic and demographic confounders, and a collection of environmental measurements.

The current state of the introduction coenopopulation of Gymnospermium odessanum on the botanical-geographical plot “Steppes of Ukraine” at the M. M. Gryshko National Botanical Garden of the NAS of Ukraine

Gymnospermium odessanum is a rare relict endemic plant species. The research was carried out during G. odessanum flowering in 2019–2021 at the botanical-geographical plot “Steppes of Ukraine” of the M.M. Gryshko National Botanical Garden, National Academy of Sciences of Ukraine (NBG). Ecological and coenotic conditions of introduction at the NBG differ from natural habitats of the species and are not optimal for its vegetation. However, this species demonstrated ecological-coenotic plasticity and, over the decades, has formed a stable homeostatic introduction coenopopulation here. As of 2021, the area of introduction coenopopulation of G. odessanum at the NBG was 2,075 m2. It comprises 412 individuals of this species (including 40 seedlings, 241 juvenile, 45 immature, 40 virginal, 45 generative, and 1 sub-senile plants). Coenopopulation fragments with a high density of G. odessanum individuals are rare here, so the average density is low – only 0.2 individuals per 1 m2. In 2021, in the spectrum of age states, the total percentage of pregenerative individuals was very high and reached 88.8 %; the share of generative individuals was 10.9 %.In general, the age structure of the introduction coenopopulation of G. odessanum is characterized by long-term (2010–2021) stability. The spatial distribution of individuals in the introduction coenopopulation is of two kinds – random and in groups. This is due to combined myrmecochoric and barochoric propagation. Also due to myrmecochory, this coenopopulation tends to spread the area. Compared to natural coenopopulations, the introduction coenopopulation of G. odessanum at the NBG is characterized by a larger area, a much significant number, and, at the same time, a low average density of individuals. However, like in most of natural populations, its age spectrum is left-sided.The conducted research testifies the successful formation of the introduction coenopopulation of G. odessanum in the meadow-steppe cultural phytocoenosis of the NBG. This introduction coenopopulation is an example of a successful multi-year scientific experiment and effective ex situ protection and preservation of G. odessanum on the northern border of the Right Bank Forest-Steppe of Ukraine, far beyond the natural range of this endemic plant species.

Identifying relationships between personal social networks and spatial mobility: A study using smartphone tracing and related surveys

Knowledge about the relationship between the spatial organisation of personal social networks and physical mobility is important for understanding spatial problems and social inequalities that are inseparable from spatial and social structures. To provide further insights into these relationships, this study investigates the link between the spatial distribution of individuals’ social networks and spatial mobility. We collected data from a group of ‘highly skilled’ individuals with a smartphone application and combined quantitative surveys. In general, individuals with dispersed networks tend to have more spatial mobility. Our typological approach reveals three distinctive types: (A) dispersed networks and high mobility, (B) dispersed networks and low mobility, and (C) concentrated networks and low mobility. This typology is explained by gender, the composition of the network, and the use of mobile phones and social media.

Ecological compensation: How much and where?

We develop a normative approach to optimal environmental compensation in a spatial framework. We determine both the location and the level of compensation that minimize the total cost of restoration while maintaining the social welfare unchanged. In our framework, the policy maker implements a No Net Loss policy that meets the No Worse-Off principle as well as a location constraint on the offset. We describe the additional ecological cost induced by the No Worse-Off principle and how the spatial distribution of individuals, the environment and land costs affect the compensation location. The location constraint is shown to give rise to a trade-off between the compensation cost and the inequality among individuals induced by the policy.

Relating the Strength of Density Dependence and the Spatial Distribution of Individuals

Spatial patterns in ecology contain useful information about underlying mechanisms and processes. Although there are many summary statistics used to quantify these spatial patterns, there are far fewer models that directly link explicit ecological mechanisms to observed patterns easily derived from available data. We present a model of intraspecific spatial aggregation that quantitatively relates static spatial patterning to negative density dependence. Individuals are placed according to the colonization rule consistent with the Maximum Entropy Theory of Ecology (METE), and die with probability proportional to their abundance raised to a power α, a parameter indicating the degree of density dependence. This model can therefore be interpreted as a hybridization of MaxEnt and mechanism. Our model shows quantitatively and generally that increasing density dependence randomizes spatial patterning. α = 1 recovers the strongly aggregated METE distribution that is consistent with many ecosystems empirically, and as α → 2 our prediction approaches the binomial distribution consistent with random placement. For 1 < α < 2, our model predicts more aggregation than random placement but less than METE. We additionally relate our mechanistic parameter α to the statistical aggregation parameter k in the negative binomial distribution, giving it an ecological interpretation in the context of density dependence. We use our model to analyze two contrasting datasets, a 50 ha tropical forest and a 64 m2 serpentine grassland plot. For each dataset, we infer α for individual species as well as a community α parameter. We find that α is generally larger in the tightly packed forest than the sparse grassland, and the degree of density dependence increases at smaller scales. These results are consistent with current understanding in both ecosystems, and we infer this underlying density dependence using only empirical spatial patterns. Our model can easily be applied to other datasets where spatially explicit data are available.

Competition Restricts the Growth, Development, and Propagation of Carpinus tientaiensis: A Rare and Endangered Species in China

The protection and propagation of rare and endangered species are key to the preservation of their population development; however, due to the scarcity of individuals, the potential effects and status of rare and endangered species in the whole forest ecosystem are still poorly understood. Using data from a 60 × 140 m forest dynamic monitoring sample of the Carpinus tientaiensis (Betulaceae) species in Zhejiang of Southeast China. We assessed the population distribution and diameter at breast height (DBH) structure of the Carpinus tientaiensis species, which was a rare and endangered species, as well as intra- and interspecific correlation with other species. The results show that saplings (1 cm ≤ DBH < 5 cm) and juveniles (5 cm ≤ DBH < 10 cm) were more aggregated than larger individuals (DBH ≥ 20 cm) of Carpinus tientaiensis. The DBH size structure of all the trees shows an obvious inverted “J” distribution. With an increase in the DBH size category, the number of individuals gradually decreases. Due to the diffusion limitation, the spatial distribution patterns of all the tree individuals and roof geese in the sample land are increased at a small spatial scale, and as the spatial scale increases, the degree of aggregation decreases gradually. The relationship between different diameter stages of the population of Carpinus tientaiensis showed a consistent general trend. The spatial distribution of individuals with a large diameter on a small scale was significantly positively correlated (p < 0.001). With an increase in the scale, there was no significant correlation (p > 0.05) between individuals with a large diameter and individuals with a small diameter. There was no significant correlation (p > 0.05) between the population of Carpinus tientaiensis and other species in the sample, and the strong unidirectional competition of other species in the sample can be seen by the competition index. We found that interspecific competition restricts the growth and expansion of Carpinus tientaiensis, and it has adopted different ecological strategies to coexist with a population of common tree species occupying a similar living space.

Formation of the introduced coenopopulation of Crocus reticulatus on the botanical-geographical plot “Steppes of Ukraine” at the M. M. Gryshko National Botanical Garden of the NAS of Ukraine

The research was carried out during Crocus reticulatus flowering time in 2002–2020 at the botanical-geographical plot “Steppes of Ukraine” of the M.M. Gryshko National Botanical Garden, National Academy of Sciences of Ukraine (NBG). Crocus reticulatus was introduced to the NBG from the natural habitats in 2002–2003. Ten generative individuals were planted in an area of 2 m2. The area of coenopopulation and the number of individuals increased gradually until 2018. In 2019–2020, there was a rapid increase in the covered area and number of individuals. However, the average density of individuals decreased. The percentage of pregenerative plants (juvenile, immature, and virginal) increased, and the percentage of generative individuals decreased. As of 2020, the area of introduced coenopopulation of C. reticulatus at the NBG reached 195 m2. It consists of 175 individuals (38 juvenile, 21 immature, 23 virginal, and 93 generative). The average density is 0.9 individuals per 1 m2. The spatial distribution of individuals is characterized as random and in groups. This is due to the predominance of the myrmecochoric and barochoric propagation. Indicators of the area, number, and average density of the introduced coenopopulation are within the normal ranges of the natural populations; however, they are smaller than those in maternal populations. The number of individuals of different age states and the number of individuals with one and two or three flowers in the introduced coenopopulation is close to such parameters of the natural population from Kyiv Plateau. Flowers of different colors were observed both in the introduced coenopopulation and in natural populations of C. reticulatus. As of 2020, the introduced coenopopulation of C. reticulatus is in the phase of logistic growth.

Community Outbreak Investigation of SARS-CoV-2 Transmission Among Bus Riders in Eastern China

Evidence of whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19), can be transmitted as an aerosol (ie, airborne) has substantial public health implications. To investigate potential transmission routes of SARS-CoV-2 infection with epidemiologic evidence from a COVID-19 outbreak. This cohort study examined a community COVID-19 outbreak in Zhejiang province. On January 19, 2020, 128 individuals took 2 buses (60 [46.9%] from bus 1 and 68 [53.1%] from bus 2) on a 100-minute round trip to attend a 150-minute worship event. The source patient was a passenger on bus 2. We compared risks of SARS-CoV-2 infection among at-risk individuals taking bus 1 (n = 60) and bus 2 (n = 67 [source patient excluded]) and among all other individuals (n = 172) attending the worship event. We also divided seats on the exposed bus into high-risk and low-risk zones according to the distance from the source patient and compared COVID-19 risks in each zone. In both buses, central air conditioners were in indoor recirculation mode. SARS-CoV-2 infection was confirmed by reverse transcription polymerase chain reaction or by viral genome sequencing results. Attack rates for SARS-CoV-2 infection were calculated for different groups, and the spatial distribution of individuals who developed infection on bus 2 was obtained. Of the 128 participants, 15 (11.7%) were men, 113 (88.3%) were women, and the mean age was 58.6 years. On bus 2, 24 of the 68 individuals (35.3% [including the index patient]) received a diagnosis of COVID-19 after the event. Meanwhile, none of the 60 individuals in bus 1 were infected. Among the other 172 individuals at the worship event, 7 (4.1%) subsequently received a COVID-19 diagnosis. Individuals in bus 2 had a 34.3% (95% CI, 24.1%-46.3%) higher risk of getting COVID-19 compared with those in bus 1 and were 11.4 (95% CI, 5.1-25.4) times more likely to have COVID-19 compared with all other individuals attending the worship event. Within bus 2, individuals in high-risk zones had moderately, but nonsignificantly, higher risk for COVID-19 compared with those in the low-risk zones. The absence of a significantly increased risk in the part of the bus closer to the index case suggested that airborne spread of the virus may at least partially explain the markedly high attack rate observed. In this cohort study and case investigation of a community outbreak of COVID-19 in Zhejiang province, individuals who rode a bus to a worship event with a patient with COVID-19 had a higher risk of SARS-CoV-2 infection than individuals who rode another bus to the same event. Airborne spread of SARS-CoV-2 seems likely to have contributed to the high attack rate in the exposed bus. Future efforts at prevention and control must consider the potential for airborne spread of the virus.

Migration route, stopping sites, and non-breeding destinations of adult Black-tailed Godwits breeding in southwest Frysl\xe2n, The Netherlands

In this paper, we extend our understanding of the migration of Black-tailed Godwits (Limosa limosa limosa) by describing: (1) the orientation and geographic locations of individual migratory routes and (2) the spatial distribution of godwits across seasons and years. We accomplish this using satellite-tracking data from 36 adult godwits breeding in the 200-ha Haanmeer polder in The Netherlands, from 2015 to 2018. During both southward and northward migration, godwits used a narrow migratory corridor along which most individuals made stops within a network of sites, especially the Bay of Biscay, France and Doñana, Spain. Most sites were used consistently by the same individuals across years. However, sites in Morocco were used during northward migration by 75% of individuals, but not revisited by the same individual across years. After southward migration, a small proportion (15%) of godwits spent the entire non-breeding period north of the Sahara, but most (85%) crossed the Sahara and spent at least part of the non-breeding season among seven coastal sites in West Africa and one site in the Inner Niger Delta. Although site-use patterns varied among individuals, individuals showed high site fidelity and were consistent in the number of sites they used from year to year. The considerable differences in the spatial distribution of individuals that breed within a kilometre of one another raise questions about the causes and consequences of individual migratory differences. We discuss that full annual cycle tracking of juveniles from birth to adulthood is needed to understand the source of these individual differences. Our results on the spatial distribution of godwits throughout their annual cycle lay an important foundation of information that can be used to help conserve this declining species.

SPATIAL DISTRIBUTION AND STRUCTURAL VARIATION OF Copaifera arenicola IN A CAATINGA FRAGMENT

The study of spatial distribution of tree populations has proven to be important for revealing how individuals are horizontally organized in the environment, facilitating the structural understanding and forms of colonization and dispersion of propagules. The present work aimed at studying the pattern of spatial distribution of tree species Copaiferaarenicola [(Ducke) J. Costa e L.P.Queiroz] and its structural relation with the altimetric profile in a Caatinga fragment in Ribeira do Pombal municipality, Bahia. Census of all individuals in the area with circumference at breast height (CBH) ≥ 6 cm was performed. The spatial distribution analysis was conducted for the whole population using Ripley K univariate function, with maximum search radius (h) of 128 m. 409 individuals were found, corresponding to absolute density of 89.49 ind. ha-1 and 0.681 m². ha-1 of basal area. The group of C. arenicola individuals corresponds to a stable population in expansion phase, presenting higher number of young and medium individuals. The pattern of spatial distribution of individuals in the area under study was the uniform arrangement. None of the altimetric classes of the area had a different influence on the structure and distribution of arboreal individuals.

Factors driving sexual dimorphism and colour variability in the Achala Copper Lizard (Pristidactylus achalensis), an endemic species to the highland mountains in central Argentina

The intensity of mating competition varies according to the temporal and spatial distribution of individuals. Measuring sexual dimorphism over time and interpreting the association between individuals is therefore important if we aim to understand how sexual traits are influenced. We examined sex differences in the Achala Copper Lizard (Pristidactylus achalensis (Gallardo, 1964)), an endemic species from the highest part of mountains of central Argentina. Over 4 years, we explored sex-specific variation in body size, head size, interlimb length, and body colouration. Furthermore, we evaluated how these traits varied temporally, and we also explored whether the spatial distribution of individuals is explained by variation in these traits. We found that P. achalensis is a species with sexual dimorphism in multiple characters, including body size, head size, and colouration. Interestingly, some traits related to mating, such as head width, show a temporal variability in both sexes, whereas other traits, such as colouration, varies seasonally only in males. Our results underline the intriguing possibility of seasonal morphological changes related to mating, and more broadly that sex differences are influenced by sexual selection pressures mediated by temporal variation in mate competition.

Avoidance and aggregation create consistent egg distribution patterns of congeneric caddisflies across spatially variable oviposition landscapes.

Amongst oviparous animals, the spatial distribution of individuals is often set initially by where females lay eggs, with potential implications for populations and species coexistence. Do the spatial arrangements of oviposition sites or female behaviours determine spatial patterns of eggs? The consequences of spatial patterns may be context independent if strong behaviours drive patterns; context dependent if the local environment dominates. We tested these ideas using a guild of stream-dwelling caddisflies that oviposit on emergent rocks, focussing on genera with contrasting behaviours. In naturally occurring oviposition landscapes (riffles with emergent rocks), we surveyed the spatial arrangement and environmental characteristics of all emergent rocks, identified and enumerated egg masses on each. Multiple riffles were surveyed to test for spatially invariant patterns and behaviours. In landscapes, we tested for spatial clumping of oviposition sites exploited by each species and for segregation of congeneric species. At oviposition sites, we characterised the frequency distributions of egg masses and tested for species associations. Genus-specific behaviours produced different spatial patterns of egg masses in the same landscapes. Congregative behaviour of Ulmerochorema spp. at landscape scales and an aggregative response at preferred oviposition sites led to clumped patterns, local aggregation and species overlap. In contrast, avoidance behaviours by congeners of Apsilochorema resulted in no or weak clumping, and species segregation in some landscapes. Spatial patterns were consistent across riffles that varied in area and oviposition site density. These results suggest that quite different oviposition behaviours may be context independent, and the consequences of spatial patterns may be spatially invariant also.