Anthropogenic Regimes Research Articles

Редкие и исчезающие виды растений: популяционный аспект в изучении и охране

The article provides an overview of areas of population research on rare and endangered plant species. It is noted that recommendations for implementing the strategy for protecting biodiversity can only be implemented through a comprehensive study of rare and endangered species. To select objects of protection and compile a list of Red Book species (regional strategy), study biology, ecology, assess the state of populations and select methods for their protection (species strategy), many approaches are used, among which the most common are: ecological-phytocenotic, population-ontogenetic and demographic , vital, phenetic, complex. These approaches involve conducting a geobotanical description of phytocenoses with rare species, determining demographic indicators (density, abundance, ratio of age groups) and determining the size of populations, as well as intravital measurement of the morphometric characteristics of vegetative and reproductive above-ground organs. Based on syntaxonomic analysis of geobotanical descriptions, the phytocenotic areas of the species are determined. Based on geobotanical descriptions using environmental scales, connections between species and environmental factors and anthropogenic regime are established, as well as ecological tolerance and valence of species. The result of the implementation of the ecological-phytocenotic approach when studying rare species is the identification of limiting factors of a natural and anthropogenic nature. To analyze the state of populations based on demographic indicators, population indices are widely used: recovery index, aging index, population optimum index, cenopopulation consistency in the “delta-omega” system, which distinguishes 6 demographic types. The state of populations is also assessed by the ratio of plant life groups. To select effective measures to protect species and populations, it is proposed to use the strategic potential of plants, assessed by natural changes in the integrity of the morphological structure of plants along an environmental gradient towards increasing stress. The article provides examples of the implementation of the listed approaches and methods into the practice of protecting rare species on the territory of the Russian Federation and the Republic of Bashkortostan.

Desertification hazards in the middle zone of Wadi Fatimah, West Saudi Arabia

This research aims at determining and analysing the causes and consequences of desertification in the middle zone of Wadi Fatimah using satellite images, climatic data, and topographic maps. The climatic parameters such as temperature, rainfall, and global reference evapotranspiration (ET0) indicated common severe arid conditions in the study area. The CORONA images acquired in 1967 and 1979 along with the topographic map of 1971 helped define the initial morphologic features and anthropogenic regimes. Analysing the various spatial datasets implied that the inappropriate management of water resources has resulted in changes in the anthropogenic regimes in the middle zone of Wadi Fatimah. These changes have triggered a chain of desertification processes such as degradation of the vegetation biomass and wind activities. These processes have transformed 15.3 km2 of agricultural farms into abandoned lands. Nineteen km2 of bushes have disappeared as well. The degradation of both agricultural and natural vegetation has exposed soils to intense wind erosion that detaches, transports and deposits sand in areas of low elevations. Accordingly, sand accumulations have massively expanded from 16.4 km2, as monitored by 1967 CORONA images, to 40.8 km2, as monitored by SPOT in 2013. This research emphasises that the middle zone of Wadi Fatimah has been experiencing remarkable changes in its morphologic and environmental characteristics in response to serious desertification processes. These processes are strongly linked to many anthropogenic interventions. It became a necessity, then, to redefine, study and assess the various anthropogenic parameters and their relative roles in desertification processes to combat desertification hazards and enhance sustainable environmental context in the middle zone of Wadi Fatimah.

Changes in the Thickness of Ice Cover on Water Bodies Subject to Human Pressure (Silesian Upland, Southern Poland)

The paper discusses the reasons behind the variation in the thickness of ice on 39 anthropogenic water bodies located in the Silesian Upland (southern Poland). The studies were conducted over the course of three consecutive winter seasons. The measurements and observations were scheduled every 2 days during the freezing and ablation of the ice, and every 4 days when ice cover was present. Each time the thickness of the ice cover and the snow layer covering it were measured. The results show that the 35 water bodies studied are characterized by a similar—quasi-natural—ice regime, in which ice thickness variation depends mostly on the air temperature and the thickness of the snow layer covering the ice. The ice thickness on those water bodies does not significantly differ from that observed on lakes located in northern Poland, measuring on average from circa 4 to 21 cm, and with maximum thicknesses ranging from circa 14 to 40 cm, depending on the season. Four water bodies are characterized by different ice conditions; in their case the average and maximum ice thickness was significantly lower. In the Niezdara N water body this was caused by the inflow of warmer potamic water (quasi-natural regime), whereas in Pod Borem, Sośnicka, and Somerek it was caused by discharges of warm mine water (anthropogenic regime).

Ecogeographical Variability of the Summer Bird Assemblage in the Pacific Part of Russia

Bird counts have been carried out in 794 habitats over 59 years (in separate seasons) from 1960 to 2018. Seventy-one bird watchers participated in collecting material. Based on the results of bird counting, a hierarchical classification and structural similarity graph are compiled for ornithocomplexes in the Pacific part of Russia, including Wrangel Island. The hierarchical classification contains 3 overtypes, 16 types, and 17 subtypes of the bird assemblage. The similarity graph is built at the type level and is represented by seven series (trends), two of which relate to undeveloped land communities of mainly the North Pacific and Amur-Sakhalin physico-geographical countries. One series consists of ornithocomplexes of residential and recreational territories and four series consist of water and near-water communities (mainland and marine). The given characteristics of classification taxa contain information on the five most numerous bird species (leaders in abundance), their part in communities, assemblage density, and background species richness and avifauna types that are prevailing in abundance. The composition of taxa was used as a basis to reveal 10 environmental factors and 32 natural and anthropogenic regimes that correlate with spatial heterogeneity of ornithocomplexes. The strength and generality of the variability of bird communities and their habitats are estimated.

New insights into hydropeaking mitigation assessment from a diversion hydropower plant: The GKI project (Tyrol, Austria)

Hydropeaking is an anthropogenic regime that results from the strong flow variations in the receiving waters of storage hydropower plants. These variations are due to flexible energy production, i.e. the sudden increase of electricity demands or from its decrease, affecting the fish assemblages of that river stretch. We evaluated the mitigation potential of the hydropeaking diversion hydropower plant (hd-HPP) named Gemeinschaftskraftwerk Inn - GKI, located in the Inn River at the Alpine region (Tyrol, Austria). This HPP will use a weir reservoir for the retention of hydropeaking coming from upstream HPPs, together with the diversion of peak flows, which intends to mitigate the impacts of hydropeaking along the residual flow stretch while allowing for hydropower production. Our study aims to evaluate and mitigate the stranding potential of the European grayling (Thymallus thymallus) within the time range of the species' larvae life-stage in the Inn river's studied stretch. To do so, we addressed a set of high-resolution historical hydrological data and, afterwards, the implementation of mitigation operational scenarios, for wet and dry years. The performance of the historical status and the mitigation scenario was assessed based on 1D unsteady modelling in a set of 26 cross-sections along a 6.5 km stretch, by quantifying the downramping rate and flow ratio events over the grayling larvae's tolerance thresholds to stranding (0.2 cm/min) and the Austrian legal threshold for flow ratio (1:3), respectively. Furthermore, we developed a new eco-hydromorphological assessment scheme, including topographic features that have been confirmed as stranding increase factors, besides the hydrological parameter's assessment. A qualitative classification was defined (Very High, High, Medium, Small, Low) for the species' larvae stranding potential, gathering the hydrological and morphological parameters assessment, represented in a map with the cross-section's location and assessment class. Results confirmed that the operational scenario highly reduced the number of events where downramping rate and the flow ratio were over the thresholds in all sections, with higher effectiveness in the wet year analysis, where tributaries influence showed a major role. Afterwards, for the qualitative assessment, in the historical records analysis the cross-sections status were included in the High or Medium classes of stranding potential. In the mitigation scenarios, most of sections' status shifted to the Low or Small classes. With this study, we confirmed that the GKI hydropower scheme may be considered as an effective hydropeaking mitigation strategy. Additionally, we presented a novel 1D-based approach for stranding potential assessment, grounded on a cost-effective and integrative classification scheme.

Number and Distribution of the Narrow-Headed Vole Lasiopodomys gregalis (Pallas, 1779) (Cricetidae, Rodentia) in Western Siberia

According to the data collected in the second half of summer for the period from 1954 to 2016 in the flat and mountainous parts of Western Siberia, the distribution and number of the narrow-headed vole in the zonal and provincial aspects were analyzed. Based on the cluster analysis of the matrix of similarity coefficients of abundance indicators obtained by averaging the initial data by years and groups of geobotanical maps units, the classification of habitats according to the favorable environmental conditions degree for the vole is made. The averaged samples are divided into five types of favorability: from optimal, where the abundance of the species is highest in the whole studied area, to extreme, where it is not encountered. In the South of the West Siberian plain narrow-headed vole prefers steppes, and in the subarctic tundras – communities of river valleys. In the Altai and Kuznetsk-Salair mountain regions it is most common in the subalpine light forests, tundras and tundra-steppe of the North-Western and SouthEastern Altai. On average, this vole prefers open habitats in Western Siberia. According to the classification and the structural graph, the dependence of the vole abundance on a number of factors and their inseparable combinations (enviromental and anthropogenic regimes) was revealed. The greatest connection with its distribution in the habitats of Western Siberia is traced for heat and water availability. On the plain, the number of this vole increases from the middle taiga, where it is found only once, to the subzone of the subarctic tundras in the North and to the forest-steppe and steppe zones in the South. In the mountains its more in the South-Eastern Altai, where a relatively high proportion of the most favorable for narrow-headed vole habitats.

Characterisation of Sand Accumulations in Wadi Fatmah and Wadi Ash Shumaysi, KSA, Using Multi-Source Remote Sensing Imagery

The study area has three sand accumulations: Two in Wadi Fatmah and one in Wadi Ash Shumaysi, midwest of Saudi Arabia. The spatial extents of these sand accumulations have significantly increased over the last few decades. Multi-source satellite imagery, such as CORONA (1967, 1972), SPOT 5 (2013), LandSat TM (1986), and LandSat 8 OLI (2013), enabled monitoring and analysis of the interplay between the changes in the anthropogenic activities and spatial expansion of the areas of sand accumulation. The main driving force of the spatial expansion could be strongly linked to extensive changes in the anthropogenic regimes in the middle zone of Wadi Fatmah and its surrounding landforms and mountain masses. In this context, the once dominant agricultural lands of the middle zone of Wadi Fatmah have been transformed into abandoned agricultural areas. Extensive off-road driving has resulted in soil degradation. Excavation and mining activities for urban spatial expansion are widespread over the valley floor, the adjacent bajada, and the mountain blocks. These anthropogenic activities have remarkably induced strong wind erosion of the soil in severe arid conditions in the middle zone of Wadi Fatmah and Wadi Ash Shumaysi. Wind erosion has eventually produced a sufficient sand budget to be transported into the areas of sand accumulation. The primary consequence of the excess sand budget has been an increase in the spatial extents and dune migration rates of sand accumulations in the study area. However, this increase varies from one sand accumulation to another. In this study, we used multi-source remote sensing imagery and the state-of-the-art COSI-Corr technology to characterize sand accumulations in the study area and to determine the spatio-temporal changes in both the spatial extents and the dune migration rates. The mean annual migration rates of sand dunes in the three sand accumulations ranged from 5.5 and 7.2 to 8.6 m/yr. Analysis of the spatial extent and migration rates of sand accumulations indicates that the study area may have experienced desertification in response to changes in the anthropogenic regimes through the last few decades.

Potential anthropogenic regime shifts in three freshwater lakes in Tropical East Asia

Abstract Regime shifts in ecology are characterised by major, often abrupt changes in ecosystem structure and functioning in response to one or more driving variables, or pressures. Changes in the provision of ecosystem services are a potential outcome. Despite the current combination of rapidly increasing pressures on what are often highly important socio‐ecological systems, the resilience of lakes in the warm tropics to human perturbation is far less well understood than those at higher latitudes. This paper focuses on evidence of aquatic ecosystem change from a cluster of three deep, freshwater, volcanic crater lakes (Yambo, Mohicap, and Sampaloc) at low altitude on the island of Luzon, Philippines. The lakes support different intensities of aquaculture, an important livelihood but also a driver of poor water quality throughout tropical Asia. Measured and monitored climate and water quality data, in addition to sedimentary evidence from sediment cores collected from the three study lakes, were used to determine the magnitude and trajectory of changes in lake water quality. Sediment cores were radiometrically dated and analysed for organic matter, spheroidal carbonaceous particles, and diatom remains. Diatom data were zoned numerically using cluster analysis. Diatom remains were also used to infer past variations in pH and possible relationships between potential driving climatic variables (temperature and rainfall). Diatom data sets were explored using detrended component analysis and principle component analysis. Despite differences in intensity of aquaculture, a common trajectory and timing of a potential regime shift, characterised by a replacement of benthic with planktonic diatoms and an increase in diatom accumulation rates from the early to mid‐1980s, is evident, and attests a low threshold for disturbance effects. A predominantly planktonic diatom flora has persisted even after recent improvements in environmental quality. The potential new regime may be less resilient and more susceptible to harmful algal blooms, abrupt expansions of anoxic conditions, and periodic mass fish kills when compared with its former state. The research further highlights the sensitivity of freshwater ecosystems in the warm tropics to disturbance pressures, and the risks to livelihoods, ecosystem services, and sustainable development.

Analysis of the stability of water bodies to the action of destabilizing factors

Methodical approaches to the assessment of ecological safety of ecosystems based on the establishment of a comprehensive indicator of the degradation of environmental components have been developed, which will allow us to assess non-additive properties of different-scale aquatic ecosystems. The analysis of methods for assessing the stability of water bodies to change the parameters of natural and anthropogenic regimes is carried out. Investigation of the nature of resistance of water bodies has revealed not only their desire for balance, but also a complex fight against regular and irregular (fluctuations) forces.

Modeling terrestrial ecosystem productivity of an estuarine ecosystem in the Sundarban Biosphere Region, India using seven ecosystem models

The net primary production (NPP) is a key indicator for assessing the terrestrial carbon pools and fluxes from the atmosphere to biosphere in any given ecosystem. Adequate measurement of the sensitivity and uncertainty of regional and global carbon pools and fluxes in different climatic and anthropogenic regimes is needed to properly investigate the terrestrial carbon balance. Remote sensing light use efficiency (LUE) approaches can be used to quantify the terrestrial NPP accurately. Using LUE models, NPP was calculated for last two decades of an estuarine ecosystem, the Sundarban Biosphere region, India. Results from seven LUE models: Carnegie-Ames-Stanford Approach (CASA), Global Production Efficiency Model (GLO-PEM), Vegetation Photosynthesis Model (VPM), Eddy Covariance-Light Use Efficiency (EC-LUE), MODerate resolution Imaging Spectroradiometer (MOD17), Temperature and Greenness (TG), Greenness and Radiation (GR) models were compared to ascertain model consistency for NPP estimation during the study period 2000–2013. To optimize structural biases in the model accurate parameterization and systematic multi-method assessment were employed. The influence of the input drivers (biophysical, bioclimatic and environmental stress) on model performances was evaluated. Best model performances were observed over cropland, followed by mixed forest and mangrove ecoregion, respectively. Amongst all model, EC-LUE simulated higher NPP at mangrove ecoregion, while the MOD17 model simulated lower NPP in most of the evaluated biomes. In addition, TG and GR models exhibited larger unexplained variances and found statistically significant at mixed forest site. This error was attributed to the absence of environmental stress factors used to drive these model. GLO-PEM and VPM corroborate with NPP prediction among all LUE models. All seven LUE models predict the statistically significant NPP across the biomes and, the poor model performance is attributed to the different parameterization scheme executed for defining the biophysical and stress variables. Biophysical drivers mostly controlled the model performances, followed by environmental stress and bioclimatic drivers, respectively. This analysis is suggesting that the TG and GR model (driven only by the biophysical factors) could be useful in NPP predictions in the regions with no meteorological inputs and real-time eddy covariance flux tower measurement.

People, El Niño southern oscillation and fire in Australia: fire regimes and climate controls in hummock grasslands.

While evidence mounts that indigenous burning has a significant role in shaping pyrodiversity, the processes explaining its variation across local and external biophysical systems remain limited. This is especially the case with studies of climate-fire interactions, which only recognize an effect of humans on the fire regime when they act independently of climate. In this paper, we test the hypothesis that an anthropogenic fire regime (fire incidence, size and extent) does not covary with climate. In the lightning regime, positive El Niño southern oscillation (ENSO) values increase lightning fire incidence, whereas La Niña (and associated increases in prior rainfall) increase fire size. ENSO has the opposite effect in the Martu regime, decreasing ignitions in El Niño conditions without affecting fire size. Anthropogenic ignition rates covary positively with high antecedent rainfall, whereas fire size varies only with high temperatures and unpredictable winds, which may reduce control over fire spread. However, total area burned is similarly predicted by antecedent rainfall in both regimes, but is driven by increases in fire size in the lightning regime, and fire number in the anthropogenic regime. We conclude that anthropogenic regimes covary with climatic variation, but detecting the human-climate-fire interaction requires multiple measures of both fire regime and climate.This article is part of the themed issue 'The interaction of fire and mankind'.

Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta

Over the last half century, while the total sediment load of the Danube dramatically decreased due to dam construction on tributaries and its main stem, a grand experiment was inadvertently run in the Danube delta: the construction of a dense network of canals, which almost tripled the water discharge toward the interior of the delta plain. We use core-based and chart-based sedimentation rates and patterns to explore the delta transition from the natural to an anthropogenic regime, to understand the effects of far-field damming and near-field channelization, and to construct a conceptual model for delta development as a function sediment partition between the delta plain and the delta coastal fringe. We show that sediment fluxes increased to the delta plain due to channelization counteracting sea level rise. In turn, the delta coastal fringe was most impacted by the Danube's sediment load collapse. Furthermore, we suggest that morphodynamic feedbacks at the river mouth are crucial in trapping sediment near the coast and constructing wave-dominated deltas or lobes. Finally, we suggest that increased channelization that mimics and enhances natural processes may provide a simple solution for keeping other delta plains above sea level and that abandonment of wave-dominated lobes may be the most long term efficient solution for protecting the internal fluvial regions of deltas and provide new coastal growth downcoast.

Comparison and assessment of the monitoring data of two REMOS stations in Nestos and Pagoneri for the year 2004. The base for an integrated water management

Abstract The monitoring results of two ‘‘REMOS’’ telemetric stations, in River Nestos, are compared. The first one is situated at the Nestos Delta, near Hrisoupoli (Remote Station – RS ‘‘Nestos’’), and the second one is situated at the course of Nestos, near the Greek-Bulgarian borders (Remote Station – RS ‘‘Pagoneri’’). The fluctuations of the qualitative and quantitative water parameters have been normalized in the Nestos Delta, following its new anthropogenic regime, whereas at the course of the river, above the power plants, important peaks are noted in the qualitative and quantitative parameters. During the statistical process of these parameters, their trend is examined and their goodness-of-fit assessment of the normal and log-normal distribution is checked, for a significance level of 5%. From the parameters that were examined for RS ‘‘Nestos’’, the water level ( H ) and the water electrical conductivity (EC w ) presented a trend, while for RS ‘‘Pagoneri’’, the same parameters did, including dissolved oxygen (DO). A linear regression model was best fitted at all of these parameters. During the goodness-of-fit test, for RS ‘‘Nestos’’ it was reported that water level ( H ) and water temperature ( T w ) follow the normal distribution (the first marginally), while air temperature ( T a ) follows the log-normal distribution. On the other hand, in RS ‘‘Pagoneri’’, none of the parameters follow a distribution.

Long-term effects of anthropogenic activities on semi-arid sand dunes

Semi-arid and arid sand dunes are considered sensitive ecosystems which may be affected by external disturbances. As many other semi-arid and arid ecosystems, their recovery ability is in the focus of many studies, whose consequences are important not only for the field of ecology but also for conservation and human welfare. I used aerial photograph analysis to study the effect of anthropogenic disturbance on dunesystem along the border between Israel and Egypt. The political changes in the border status over the last 40 years created a ‘natural’ experiment in the area, which enabled me to compare similar dune ecosystems under various anthropogenic regimes. The findings revealed a significant difference in recovery rate between the two border sides, and along the dune topography, which correspond with differences in human management (i.e. grazing and wood gathering). Nevertheless, a recovery process was detected in all parts of the dune ecosystem, even following long years of heavy anthropogenic use. The results of this study contribute to the ongoing debate about desertification processes, and indicate that some arid ecosystems may exhibit high resilience in the face of long-term exploitation.

SPATIAL CONTROLS OF OCCURRENCE AND SPREAD OF WILDFIRES IN THE MISSOURI OZARK HIGHLANDS

Understanding spatial controls on wildfires is important when designing adaptive fire management plans and optimizing fuel treatment locations on a forest landscape. Previous research about this topic focused primarily on spatial controls for fire origin locations alone. Fire spread and behavior were largely overlooked. This paper contrasts the relative importance of biotic, abiotic, and anthropogenic constraints on the spatial pattern of fire occurrence with that on burn probability (i.e., the probability that fire will spread to a particular location). Spatial point pattern analysis and landscape succession fire model (LANDIS) were used to create maps to show the contrast. We quantified spatial controls on both fire occurrence and fire spread in the Midwest Ozark Highlands region, USA. This area exhibits a typical anthropogenic surface fire regime. We found that (1) human accessibility and land ownership were primary limiting factors in shaping clustered fire origin locations; (2) vegetation and topography had a negligible influence on fire occurrence in this anthropogenic regime; (3) burn probability was higher in grassland and open woodland than in closed-canopy forest, even though fire occurrence density was less in these vegetation types; and (4) biotic and abiotic factors were secondary descriptive ingredients for determining the spatial patterns of burn probability. This study demonstrates how fire occurrence and spread interact with landscape patterns to affect the spatial distribution of wildfire risk. The application of spatial point pattern data analysis would also be valuable to researchers working on landscape forest fire models to integrate historical ignition location patterns in fire simulation.

Impact of Protected Areas and Land Use on Regeneration of Acacia Woodland’s in Eastern Burkina Faso

Regeneration success, persistence strategies (seedlings vs. coppicing), and population trend of Acacia spp. were tested under two land-use regimes in eastern Burkina Faso: (i) protected areas shielded to livestock grazing pressure, to logging, and using early annual fire as a management system; (ii) areas with high human impact (heavily and extensive livestock grazing, harvesting for wood and for medicinal plants). Generally, a good regeneration rate of Acacia species was observed in protected areas and a poor regeneration rate in areas with high human impact. Nevertheless, some species affiliated to the subgenus Aculeiferum as A. dudgeoni and A. polyacantha showed a good regeneration under both land use regimes. Juvenile plants less than 25 cm height of A. dudgeoni and A. gourmaensis increased by 116 to 50 % in areas with human impact as compared to their populations in protected areas. With SCD slopes varying from –0.40 to -0.70, the protected Acacia woodland displayed a stable population structure due to abundance of recruitment, and coppicing persistence (more common in the subgenus Aculeiferum) favoured by early annual fire. Consequently, the protected areas are favourable for Acacia woodland regeneration. Conversely, SCD slopes are positive or close to zero in areas of anthropogenic regime and showed a declining population, especially more marked with the subgenus Acacia due to permanent seed and seedling removal by livestock grazing. Nevertheless, the number of seedlings of some species was higher in areas under human pressure than in protected areas, especially for the subgenus Aculeiferum, improving the genetic variability and thus the long-term maintenance of the population

Dispersal patterns among three species of squirrel monkeys (Saimiri oerstedii, S. boliviensis and S. sciureus): II. Within-species and local variation

AbstractThree long-term field studies, together with numerous supplementary sources of information, demonstrate that the Neotropical squirrel monkey, genus Saimiri (Primates: Cebidae) are distinguished among mammals by the wide divergence in dispersal patterns among congeners. Both sexes of Saimiri sciureus at Raleighvallen in the Central Suriname Nature Reserve undertake dispersal on several to many occasions during their lifetime. Male dispersal and female philopatry characterize S. boliviensis studies at Manu, Peru. Among S. oerstedii, studied at Corcovado and other locations in Costa Rica, females disperse and males are philopatric. This is the second in a series of three companion reports investigating patterns and processes relevant to dispersal in these three species of squirrel monkeys. The first report, I. Divergent costs and benefits (Boinski et al., 2005), predicts the direct and inclusive fitness costs and benefits structuring species, sex and individual dispersal strategies among squirrel monkeys. III. Cognition (Boinski, 2005), the final report comprising this monograph, considers the possible cognitive mechanisms underlying dispersal among squirrel monkeys and other taxa, and suggests useful strategies to collect and interpret additional data from laboratory and field contexts.Here we evaluate the sources and potential magnitude of variation in dispersal strategies within each squirrel monkey species. For all three congeners, local edaphic and anthropogenic regimes of habitat disturbance probably represent the major source of within-species variance in the density of wild populations. Squirrel monkey population density, all else being equal, positively increases with the intensity of habitat disturbance. New evidence suggests that in addition to edaphic and recent historical disturbance regimes, in some localities in the Neotropical lowlands anthropogenic disturbance caused by pre-Columbian Amerindians remains a potent factor enhancing squirrel monkey numbers.Squirrel monkeys are predicted to exhibit density-dependent behavioural responses. In turn, these responses are expected to modulate population-level dispersal outcomes in several predictable axes. Major between-site variation in dispersal strategies, however, is unlikely for either sex among S. oerstedii or S. boliviensis. Although all natal male S. sciureus almost certainly disperse before or at the time of sexual maturity, the proportion of females emigrating from a S. sciureus troop appears more variable, dependent on local levels of within-troop competition for food. In any year or season, those mature and immature female S. sciureus with high priority access to food resources are least likely to disperse.