Populations In Natural Environments Research Articles

Genomic evidence of genuine wild versus admixed olive populations evolving in the same natural environments in western Mediterranean Basin.

Crop-to-wild gene flow is a mechanism process widely documented, both in plants and animals. This can have positive or negative impacts on the evolution of admixed populations in natural environments, yet the phenomenon is still misunderstood in long-lived woody species, contrary to short-lived crops. Wild olive Olea europaea L. occurs in the same eco-geographical range as domesticated olive, i.e. the Mediterranean Basin (MB). Moreover, it is an allogamous and anemophilous species whose seeds are disseminated by birds, i.e. factors that drive gene flow between crops and their wild relatives. Here we investigated the genetic structure of western MB wild olive populations in natural environments assuming a homogenous gene pool with limited impact of cultivated alleles, as previously suggested. We used a target sequencing method based on annotated genes from the Farga reference genome to analyze 27 western MB olive tree populations sampled in natural environments in France, Spain and Morocco. We also target sequenced cultivated olive tree accessions from the Worldwide Olive Germplasm Bank of Marrakech and Porquerolles and from an eastern MB wild olive tree population. We combined PCA, sNMF, pairwise FST and TreeMix and clearly identified genuine wild olive trees throughout their natural distribution range along a north-south gradient including, for the first time, in southern France. However, contrary to our assumption, we highlighted more admixed than genuine wild olive trees. Our results raise questions regarding the admixed population evolution pattern in this environment, which might be facilitated by crop-to-wild gene flow.

EFFECTS OF RADIO FREQUENCY EXPOSURE ON HATCHING RATE AND DEVELOPMENT PERIOD OF AE. ALBOPICTUS (SKUSE) (DIPTERA: CULICIDAE)

Telecommunication technologies such as radio, cell phones, and television were developed to meet people's needs and have been widely used for decades. However, the invention relies on the transmission and reception of signals via radio (RF), which has increased concerns about the effects of RF fields on human health, including mosquito-borne diseases caused by exposure to these fields. To address these concerns, a study was conducted to evaluate the effects of exposure from RF on mosquitoes. The objective of this study is to determine the effects of exposure RF on hatching rate, development time, and egg morphology of the Aedes population. Under laboratory conditions, 50 Ae. albopictus eggs were exposed to three different exposures (control, low dose: 900 MHz and high dose: 18 GHz). The effects of exposure on hatching rate, development time and egg morphology were observed. This study revealed that higher doses of RF can shorten the hatching days of Aedes mosquitoes, but also slow down their development rate. In summary, this study provides important insights into the potential effects of exposure to RF on Aedes mosquito populations. Further research is needed to fully understand the effects of exposure RF on mosquito populations in natural environments and the potential public health implications.

Environmental, mechanistic and evolutionary landscape of antibiotic persistence.

Recalcitrant infections pose a serious challenge by prolonging antibiotic therapies and contributing to the spread of antibiotic resistance, thereby threatening the successful treatment of bacterial infections. One potential contributing factor in persistent infections is antibiotic persistence, which involves the survival of transiently tolerant subpopulations of bacteria. This review summarizes the current understanding of antibiotic persistence, including its clinical significance and the environmental and evolutionary factors at play. Additionally, we discuss the emerging concept of persister regrowth and potential strategies to combat persister cells. Recent advances highlight the multifaceted nature of persistence, which is controlled by deterministic and stochastic elements and shaped by genetic and environmental factors. To translate in vitro findings to in vivo settings, it is crucial to include the heterogeneity and complexity of bacterial populations in natural environments. As researchers continue to gain a more holistic understanding of this phenomenon and develop effective treatments for persistent bacterial infections, the study of antibiotic persistence is likely to become increasingly complex.

Plasticity in resource use explains the persistence of the largest living rodent in anthropized environments

AbstractHow organisms search for and obtain food is a determinant of their survival. It has been hypothesized that organisms facing food limitations might expand their dietary niche compared with optimal foraging conditions. Nonetheless, some organisms may reduce their dietary niche due to limiting resources. Here, we show the resource use plasticity of capybaras (Hydrochoerus hydrochaeris), the largest living rodent, in natural and anthropized environments of Brazil using stable carbon and nitrogen isotopes in hair. We assessed the resource use, size and overlap of isotopic niches, and the influence of body mass, age class, sex, and landscape composition on isotopic values among 13 capybara populations (210 individuals). We observed a wide variation in isotopic values of capybaras among and within populations in different environments. Surprisingly, diets varied from strictly C4‐based to strictly C3‐based, with most individuals feeding on C4 plants (65%). A substantial portion of individuals presented mixed diets (C3 and C4 plants), totaling 31% of the individuals, and few fed exclusively on C3 plants (4%). Isotopic niche size also varied among populations in both environments, with low overlap considering their core dietary niche. Capybara populations in natural environments had substantial incorporation of C3 resources, showing individuals with strictly C3 diets, and possibly relying on a high diversity of food items, while some populations in anthropized ones fed exclusively on C4 resources. Neither body mass, age class, sex, nor landscape composition significantly influenced isotopic values. Here, we provide evidence of the dietary plasticity of capybaras in different environments, transitioning from the consumption of C4 to C3 plants when needed, that is, from preferred to non‐preferred food items. Together with the species' behavioral plasticity, our results help explain its resilience in surviving, and even thriving, in both natural and human‐modified environments.

A Dynamic Detection Method for Phenotyping Pods in a Soybean Population Based on an Improved YOLO-v5 Network

Pod phenotypic traits are closely related to grain yield and quality. Pod phenotype detection in soybean populations in natural environments is important to soybean breeding, cultivation, and field management. For an accurate pod phenotype description, a dynamic detection method is proposed based on an improved YOLO-v5 network. First, two varieties were taken as research objects. A self-developed field soybean three-dimensional color image acquisition vehicle was used to obtain RGB and depth images of soybean pods in the field. Second, the red–green–blue (RGB) and depth images were registered using an edge feature point alignment metric to accurately distinguish complex environmental backgrounds and establish a red–green–blue-depth (RGB-D) dataset for model training. Third, an improved feature pyramid network and path aggregation network (FPN+PAN) structure and a channel attention atrous spatial pyramid pooling (CA-ASPP) module were introduced to improve the dim and small pod target detection. Finally, a soybean pod quantity compensation model was established by analyzing the influence of the number of individual plants in the soybean population on the detection precision to statistically correct the predicted pod quantity. In the experimental phase, we analyzed the impact of different datasets on the model and the performance of different models on the same dataset under the same test conditions. The test results showed that compared with network models trained on the RGB dataset, the recall and precision of models trained on the RGB-D dataset increased by approximately 32% and 25%, respectively. Compared with YOLO-v5s, the precision of the improved YOLO-v5 increased by approximately 6%, reaching 88.14% precision for pod quantity detection with 200 plants in the soybean population. After model compensation, the mean relative errors between the predicted and actual pod quantities were 2% to 3% for the two soybean varieties. Thus, the proposed method can provide rapid and massive detection for pod phenotyping in soybean populations and a theoretical basis and technical knowledge for soybean breeding, scientific cultivation, and field management.

Spatial Patterns of Ceroxylon parvifrons (Engel) H.Wendl of the Montane Forests in Southern Ecuador

The species of the genus Ceroxylon have narrow geographical ranges, and subsequently, their populations are subjected to a high degree of fragmentation due to deforestation and land conversion. Ceroxylon parvifrons (Engel) H. Wendl is a representative floristic species of the Andean rainforest; however, little information related to its natural history, ecology, biology, and conservation status is available, making it difficult to assess its biological relationship with the environmental factors and the current status of their populations in natural environments. Here, we studied the spatial pattern of adults, rosettes, and seedlings of C. parvifrons in the montane rainforest and assessed the role of populations’ spatial structure and intraspecific interactions on plant performance. A total of 460 individuals were categorized according to their size, with 11 adults, 10 juveniles, 336 rosettes, and 103 seedlings being recorded. C. parvifrons showed that the population is expanding during the first two stages of the plant (seedling and rosette). After this, there is a significant decrease where the frequency of individuals of the juvenile and adult categories tend to disappear from the population. The L (r) function shows a robust clustering throughout the entire scale for seedlings, rosettes, and adult palms. Also, the Poisson cluster process describes a patchy distribution in which plant individuals are distributed in clumps (clusters). Thus, this approximation related to spatial patterns of C. parvifrons will provide an important step for the conservation of this species in tropical zones.

Investigating the Effects of Pesticides on Ramshorn Snails (Planorbella [Helisoma] trivolvis) Infected with Echinostoma spp.

Globally, parasite-induced diseases in humans and wildlife are on the rise, and pesticide pollution may be a contributing factor. Echinostoma spp. trematode parasites are prominent in North America, and they use ramshorn snails (Planorbella [Helisoma] trivolvis) as intermediate hosts. We investigated the impact of chronic exposure to 1 of 5 pesticide treatments (control, or 50 μg/L of atrazine, glyphosate, carbaryl, or malathion) on uninfected and Echinostoma-infected snails for 41 d in the laboratory. We recorded snail mortality, the number of egg masses laid, change in mass, and behavior. Chronic exposure to atrazine, carbaryl, and malathion significantly decreased snail survival, whereas parasite infection status or exposure to glyphosate did not. Pesticide and parasite treatments did not influence growth or behavior, but parasite infection caused complete reproductive failure in snail hosts. Our results indicated that the direct effects of pesticides could threaten snail populations in natural environments and disrupt host-parasite dynamics. Environ Toxicol Chem 2021;40:2755-2763. © 2021 SETAC.

Significance of Tumor Growth Modeling in the Behavior of Homogeneous Cancer Cell Populations: Are Tumor Growth Models Applicable to Both Heterogeneous and Homogeneous Populations?

The ability to predict and slow the spread of cancer in the human body is a task that medical professionals have been trying to accomplish for many years. Being able to give factual basis to the use of certain growth models for application in not just heterogeneous, but also homogeneous cancer cell populations is imperative to treatment research as using mathematical analysis to predict the dynamics of tumor growth allows professionals to simulate how tumors might behave in the human body. This study follows the process of single-cloning and the growth of a homogeneous cell population in a superficial environment over the course of six weeks with the end goal of showing which of five tumor growth models commonly used to predict heterogeneous cancer cell population growth (Exponential, Logistic, Gompertz, Linear, and Bertalanffy) would also best exemplify that of homogeneous cell populations. We hypothesized that the Gompertz, Linear, and Bertalanffy models would provide the best fit to the homogeneous cancer (clonal) cell population growth data while models such as the exponential and logistic model, which are most commonly associated with the growth of heterogeneous cancer cell populations in natural environments (i.e. malignant tumors), would veer off the growth data. It was shown that Gompertz and Linear functions provided the best fit for this population, while exponential and Logistic functions fell slightly behind. The data collection and analysis for this research was performed through the University of Michigan Research Labs and Solver by Frontline Systems.

First-order effects of fire and prolonged-drought effects on an undescribed semi-aquatic turtle in Atlantic rainforest in southeastern Brazil

Fire usually impose considerable impacts on fauna, including loss of habitats and microhabitats, emigrations, injuries, or death. The general arquitecture of the local environment may play an important role in the extent that fire may act and the resulting burning effects. Understanding the exact extent of the effects of fire on vertebrate populations in natural environments is usually limited by the lack of information on the number of individuals dying during the event. Semi-aquatic turtles which usually move slowly on land, may suffer serious direct effects of fire. The mortality of turtles caused by fire and drought is well documented in the northern hemisphere, but few data are available from Brazil. Here we documented the death of individuals of a semi-aquatic still undescribed turtle species, Rhinoclemmys sp. n. on a coastal plain environment in southeastern Brazil, as result of a fire and a prolonged drought. Our results indicated that fire and drought contributed to the mortality of Rhinoclemmys sp. n. in the study area.

The effects of a water-soluble alpha tetra-substituted zinc phthalocyanine derivative onArthrospira platensis-M2 strain

In this study, we have analyzed the effect a newly synthesized water-soluble alpha tetra-substituted zinc phthalocyanine (Pc) compound on superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities and biomass accumulation in the Arthrospira platensis-M2 strain to test whether this compound could be used as an algaecide or not. We found that lower concentrations (3 μg mL[Formula: see text] and 6 μg mL[Formula: see text] of Pc compound were not toxic to algae cells, as indicated by enduring biomass accumulation during the study (7 days). Higher Pc concentrations, however, were toxic and inhibited biomass accumulation. This inhibition appeared on the fourth day and persisted during the study. At higher Pc concentrations, SOD activity decreased significantly, but APX and GR activity were not affected. These results may show that Pc applications did not cause the accumulation of reactive oxygen species in Arthrospira platensis-M2 cells. Our result suggests that higher Pc concentrations did not cause oxidative stress but biomass accumulation inhibited, possibly due to some different toxicity mechanism(s), which should be carried out in the future studies. As a result, we may offer use of this compound as a means to keep under control algal populations in natural environments.

Importance of Local and Regional Scales in Shaping Mycobacterial Abundance in Freshwater Lakes.

Biogeographical studies considering the entire bacterial community may underestimate mechanisms of bacterial assemblages at lower taxonomic levels. In this context, the study aimed to identify factors affecting the spatial and temporal dynamic of the Mycobacterium, a genus widespread in aquatic ecosystems. Nontuberculous mycobacteria (NTM) density variations were quantified in the water column of freshwater lakes at the regional scale (annual monitoring of 49 lakes in the Paris area) and at the local scale (2-year monthly monitoring in Créteil Lake) by real-time quantitative PCR targeting the atpE gene. At the regional scale, mycobacteria densities in water samples ranged from 6.7×103 to 1.9×108 genome units per liter. Density variations were primarily explained by water pH, labile iron, and dispersal processes through the connection of the lakes to a river. In Créteil Lake, no spatial variation of mycobacterial densities was noticed over the 2-year monthly survey, except after large rainfall events. Indeed, storm sewer effluents locally and temporarily increased NTM densities in the water column. The temporal dynamic of the NTM densities in Créteil Lake was associated with suspended solid concentrations. No clear seasonal variation was noticed despite a shift in NTM densities observed over the 2012-2013 winter. Temporal NTM densities fluctuations were well predicted by the neutral community model, suggesting a random balance between loss and gain of mycobacterial taxa within Créteil Lake. This study highlights the importance of considering multiple spatial scales for understanding the spatio-temporal dynamic of bacterial populations in natural environments.

Predicting free‐roaming cat population densities in urban areas

AbstractAlthough free‐roaming cats can have a significant impact on the environment, and substantial resources have been invested to find humane alternatives for managing free‐roaming cat populations, there are no empirical estimates of free‐roaming cat population size in medium to large cities. In addition, little is known about factors limiting free‐roaming cat population size and distribution. Using Guelph, ON, Canada (pop: 120 000; 86.7 km2) as a case‐study, we apply replicated distance transect sampling and likelihood‐based hierarchical modelling to compare human‐mediated landscape patterns of land use, distance to roads, distance to wooded areas, building density and socio‐economic status to explain the abundance of free‐roaming cats. We then derive an empirical estimate of total population size and present a spatially explicit prediction of free‐roaming cat density across an entire city. Cat abundance was highest in residential areas and lowest in commercial and institutional areas, negatively related to median household income, and positively related to distance from woods and building density. Total population size was estimated to be 7662 (95% bootstrap CI: 6145–9966) for Guelph; free‐roaming cat density varied from 0 to 49.4 cats per ha. Our estimate overlapped with an independent estimate of indoor‐outdoor cats (11 927; 95% CI: 6361–20 989) derived from random surveys of city residents, which implies our distance transect methodology was relatively robust and unbiased. Our approach used simple geographical information that is readily available for most urban areas in North America and can be applied broadly to inform cat management in urban areas. Finally, our results suggest that free‐roaming cat density in cities could be determined by bottom‐up processes (e.g. enhanced food availability in residential areas) as well as top‐down processes (e.g. enhanced susceptibility to coyote predation near wooded areas) which are typically reserved to explain wildlife populations in natural environments.

Tracing the production and fate of individual archaeal intact polar lipids using stable isotope probing

Analysis of cellular membrane lipids has been widely applied to describe the microbial community composition in natural systems. When combined with stable isotope probing (SIP) experiments, deuterium label (D2O) uptake into lipids enables assessment of microbial biomass production. We performed SIP on methane-rich, hydrothermally-heated sediments to examine the de novo production of individual archaeal intact polar lipids (IPLs) by mesophilic anaerobic methane oxidizing group-1 archaea (ANME-1). The greatest extent of label uptake was by phosphatidyl glycerol archaeol (PG-AR), reaching 50% of the medium’s label concentration in only 10days. This indicates PG-AR as an important cell membrane lipid during the active growth phase of mesophilic ANME-1. Much less label uptake was into intact polar glycerol dibiphytanyl glycerol tetraethers (GDGTs), especially for those bound to diglycosidic head groups. The low production of these GDGTs contrasts with their predominance in ANME-1-dominated natural samples. We attribute the differential label uptake among individual IPLs to the ANME-1 tetraether biosynthetic pathway. This mechanism likely involves head-to-head condensation of two molecules of PG-AR and progressive substitution of PG by glycosidic head groups. The observation that ANME-1 invest in the synthesis of diethers during optimum growth suggests intact ARs and/or phosphate-bearing tetraethers as important biomarkers for actively growing populations in natural environments, while the diglycosidic GDGTs appear to signal stationary ANME-1 communities.

Genetic variation facilitates seedling establishment but not population growth rate of a perennial invader.

Assessing the demographic consequences of genetic variation is fundamental to invasion biology. However, genetic and demographic approaches are rarely combined to explore the effects of genetic variation on invasive populations in natural environments. This study combined population genetics, demographic data and a greenhouse experiment to investigate the consequences of genetic variation for the population fitness of the perennial, invasive herb Lupinus polyphyllus. Genetic and demographic data were collected from 37 L. polyphyllus populations representing different latitudes in Finland, and genetic variation was characterized based on 13 microsatellite loci. Associations between genetic variation and population size, population density, latitude and habitat were investigated. Genetic variation was then explored in relation to four fitness components (establishment, survival, growth, fecundity) measured at the population level, and the long-term population growth rate (λ). For a subset of populations genetic variation was also examined in relation to the temporal variability of λ. A further assessment was made of the role of natural selection in the observed variation of certain fitness components among populations under greenhouse conditions. It was found that genetic variation correlated positively with population size, particularly at higher latitudes, and differed among habitat types. Average seedling establishment per population increased with genetic variation in the field, but not under greenhouse conditions. Quantitative genetic divergence (Q(ST)) based on seedling establishment in the greenhouse was smaller than allelic genetic divergence (F'(ST)), indicating that unifying selection has a prominent role in this fitness component. Genetic variation was not associated with average survival, growth or fecundity measured at the population level, λ or its variability. The study suggests that although genetic variation may facilitate plant invasions by increasing seedling establishment, it may not necessarily affect the long-term population growth rate. Therefore, established invasions may be able to grow equally well regardless of their genetic diversity.

Genetic differentiation in the endangered myrmecophilous butterfly Niphanda fusca: a comparison of natural and secondary habitats

Niphanda fusca is an endangered myrmecophilous butterfly inhabiting environments at early stages of succession. Most of its habitats are places where succession is prevented by human activity. In some places, however, N. fusca lives in natural semi-bare areas, such as cliffs in mountains or grasslands around volcanos. We investigate the genetic structure of N. fusca in Japan and South Korea to address two questions. (1) Are populations in natural environments genetically different from those in secondary environments? and (2) Do populations in natural environments possess greater genetic diversity than those in secondary environments? The AMOVA results indicated that the populations in natural environments and those in secondary environments were differentiated to some extent; however, more than 80 % of genetic variation was found to occur within the same habitat type and within each population. We found no differences in genetic diversity between populations in the two environments. At present, we have not found a strong reason to consider populations in the two environments as different evolutionarily significant units. We think it is practical to conserve populations in natural environments at first, because in this case we need not manage habitats to protect N. fusca. We have only to inhibit habitat destruction. In contrast, in order to conserve populations in secondary environments, we would have to continue managing the habitats. This is far more difficult than inhibiting habitat destruction.

Haematological values for captive harpy eagle (Harpia harpyja)

Decreasing of harpy eagle (Harpia harpyja) populations in natural environments, mainly in non-preserved areas, makes captive population management an important contribution to genetic diversity conservation. The aim of this study is to evaluate hematological parameters for captive harpy eagles maintained at the wild animals breeding center of Itaipu Binacional, Paraná State, Brazil. Fourteen blood samples from nine harpy eagles were collected from animals of both sexes, of different ages and with no clinical signs of disease. Significant variations were found in haematological values of hematocrit, hemoglobin, mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), leukocyte, a relative number of heterophils, absolute and relative number of lymphocytes, monocytes, eosinophils, basophils and plasma protein between groups of young (less than six months old) and adult birds. Comparing males and females there was variation in the values of erythrocytes, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) on heterophils, absolute and relative number of lymphocytes, eosinophils and basophils. There was also variation in the values of red blood cells, hematocrit, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), leukocyte count, absolute number of lymphocytes, eosinophils and basophils among birds that study compared to another reference birds. Due to the limited information available on harpy eagle hematology, this study will be useful to the clinical assessment of birds maintained in captivity.

Pollination efficiency of Apis mellifera Linnaeus, 1758 (Hymenoptera, Apidae) on the monoecious plants Jatropha mollissima (Pohl) Baill. and Jatropha mutabilis (Pohl) Baill. (Euphorbiaceae) in a semi-arid Caatinga area, northeastern Brazil

Previous studies have shown the superior competitive ability of honeybees compared with native bees in the exploitation of floral resources and nesting sites besides their low efficiency in pollinating native plant species. However, there is little evidence of the effect of this invading species on autochthonous plant populations in natural environments. Thus experiments were performed to test the pollination efficiency of honeybees in two species of Jatropha (Euphorbiaceae), J. mollissima (Pohl) Baill. and J. mutabilis (Pohl) Baill., after a single flower visitation. Samplings were carried out between March and April 2006 in a hyperxerophilous shrub-arboreal Caatinga at Estação Biológica de Canudos, Bahia (9º 56´ 34" S, 38º 59´ 17" W), the property of Fundação Biodiversitas. Apis mellifera was efficient at pollinating J. mollissima (100%) and J. mutabilis (85%). This high efficiency may be explained by 1) the simple floral characteristics of both plant species, which facilitate access to the sexual organs of the plant; and 2) the body size of A. mellifera that fits the flower's dimensions.

Application of real-time PCR assay for detection and quantification of bloom-forming diatom Chaetoceros tenuissimus Meunier

Viral infection of the bloom-forming diatom Chaetoceros tenuissimus was discovered in 2008, and is now assumed to have a significant influence on the dynamics of C. tenuissimus populations in natural environments. Enumeration of C. tenuissimus and its viruses is essential when examining the host-virus relationship in situ; however, the diatom species is so small in size that its identification and counting by optical microscope is almost impossible. To resolve this problem, we have developed a TaqMan-based real-time polymerase chain reaction (PCR) method for detec- tion and quantification of C. tenuissimus. We designed primers and a TaqMan probe to target the D1 region of its 28S ribosomal RNA (rRNA) gene; the established real-time PCR was specific at the species level by testing 41 microalgal strains including C. tenuissimus. Tris-EDTA buffer-based boiling method was shown to be efficient for extracting DNA from filter-trapped C. tenuissimus cells in this study. The detection range of the established TaqMan-based real-time PCR method for C. tenuissimus was 10 1 to 10 6 cells collected on a filter; the method was applicable for C. tenuissimus

A Novel Approach to Determining a Population-Level Threshold in Ecological Risk Assessment: A Case Study of Zinc

ABSTRACT A novel approach to population-level assessment was applied in order to demonstrate its utility in estimating and managing the risk of zinc in a water environment. Much attention has been paid to population-level risk assessment, but there have been no attempts to determine a “safe” population-level concentration as an environmental criterion. Based on the published results of toxicity tests for various species, we first theoretically derived a threshold concentration at which a population size is unchanged due to the adverse effects of zinc exposure. To derive a zinc concentration that will protect populations in natural environments, we adopted the concept of species sensitivity distribution. Assuming the threshold concentrations of a set of species are log-normally distributed, we calculated the 95% protection level of zinc (PHC5 :population-level hazardous concentration of 5% of species), which is 107 μg/L. Meanwhile, the 95% protection criterion (HC5) based on conventional individual-level chronic toxicity, was calculated to be 14.6 μg/L. The environmentally “safe” concentration for a population-level endpoint is about 7 times greater than that for an individual-level endpoint. The proposed method provides guidance for a pragmatic approach to population-level ecological risk assessment and the management of chemicals.

Densities of Eastern Chipmunks (Tamias striatus) in Farmland Woodlots Decline with Increasing Area and Isolation

Habitat loss and subsequent subdivision of remaining habitat patches are considered major threats to terrestrial animal populations in natural environments. Habitat loss normally results in reduced population numbers in remaining habitat patches, whereas isolation of habitat patches affects population dynamics among them. In this study, we examined the distribution of the eastern chipmunk (Tamias striatus) in farmland woodlots. We used the Random Sample Hypothesis as a theoretical starting point in the study. By using a standard protocol to trap chipmunks in woodlots, we expected to capture approximately the same number of individuals per woodlot independent of the size of the woodlot. We found that the probability of capturing chipmunks declined with increasing size and distance to the nearest woodlots. Such a decline in densities seemed to happen even in woodlots of less than 10 ha. Large and remote woodlots tended to be surrounded by corn fields. Measured habitat and landscape variables gave no indication as to which ecological processes might have accounted for the observed pattern. Ecological factors, such as species interactions within a woodlot and movement of individuals among woodlots, should be addressed more closely experimentally.