Period Of High Mortality Research Articles

Evaluating the influence of environmental and biological factors on migration behavior and residence duration of wild subyearling Chinook Salmon in a fjord estuary using miniature acoustic transmitters

AbstractObjectiveSeaward migration and early marine residence are periods of high mortality in the lifecycle of Pacific salmon Oncorhynchus spp. The conservation of these species requires knowledge of habitat use patterns during early life to address survival bottlenecks. Using new miniaturized transmitters (V3 307‐kHz tag; Innovasea Systems), we investigated the association between biological and environmental factors and the residence behavior of subyearling Chinook Salmon Oncorhynchus tshawytscha in a fjord estuary in British Columbia.MethodsTagged wild subyearling Chinook Salmon (n = 49; 67–95 mm) were experimentally released into an estuary. Using time‐to‐event analysis and model selection, we evaluated the association between biological (size, growth, day of release) and environmental (temperature, salinity, depth, discharge, tide direction) factors and estuary residence patterns.ResultOf the 49 fish released, 36 were inferred to have exited the estuary successfully. In this sample of subyearling Chinook Salmon, the median residence duration was estimated to be 11.2 days (95% CI = 6.5–15.5). We found tide direction and salinity to be important factors influencing the probability of a fish leaving the estuary. Fish were 75% more likely to leave the estuary on an ebb tide. Higher salinity also increased the probability of a fish leaving the estuary. Fish successful in leaving the estuary displayed either direct or indirect movement patterns in the estuary, with most fish (71%) being indirect movers that made multiple trips upstream and downstream. Within the estuary, most movements occurred at night (76%), regardless of tide direction.ConclusionThis study provides the first direct measure of estuary residence duration in wild subyearling Chinook Salmon and a valuable description of movement ecology in this age‐class of fish. While this was a small study in a single year, our results indicate this estuary is likely a stopover habitat for larger subyearlings. Studies indicating the use of habitats by specific populations, as presented here, are integral to the design of habitat‐based conservation measures for mobile species.

SARS-CoV-2: Air pollution highly correlated to the increase in mortality. The case of Guadalajara, Jalisco, México.

To determine whether air pollution or changes in SARS-CoV-2 lineages lead to an increase in mortality. Descriptive statistics were used to calculate rates of infection (2020-2021). RT-PCR was used to compare viral loads from October 2020 to February 2021. Next-generation sequencing (NGS) (n=92) was used to examine and phylogenetically map SARS-CoV-2 lineages. A correlative "air pollution/temperature" index (I) was developed using regression analysis. PM2.5, PM10, O3, NO2, SO2, and CO concentrations were analyzed and compared to the mortality. The mortality rate during the last year was ∼32%. Relative SARS-CoV-2 viral loads increased in December 2020 and January 2021. NGS revealed that approximately 80% of SARS-CoV-2 linages were B.1.243 (33.7%), B1.1.222 (11.2%), B.1.1 (9%), B.1 (7%), B.1.1.159 (7%), and B.1.2 (7%). Two periods were analyzed, the prehigh- and high-mortality periods and no significant lineage differences or new lineages were found. Positive correlations of air pollution/temperature index values with mortality were found for IPM2.5 and IPM10. INO2. ISO2, and ICO but not for O3. Using ICO, we developed a model to predict mortality with an estimated variation of ∼±5 deaths per day. The mortality rate in the MZG was highly correlated with air pollution indices and not with SARS-CoV-2 lineage.

Elevated temperatures reduce population-specific transcriptional plasticity in developing lake sturgeon (Acipenser fulvescens).

Rising mean and variance in temperatures elevates threats to endangered freshwater species such as lake sturgeon, Acipenser fulvescens. Previous research demonstrated that higher temperatures during development result in physiological consequences for lake sturgeon populations throughout Manitoba, Canada, with alteration of metabolic rate, thermal tolerance, transcriptional responses, growth and mortality. We acclimated lake sturgeon (30-60 days post fertilization, a period of high mortality) from northern and southern populations (56°02'46.5″N, 96°54'18.6″W and 50°17'52″N, 95°32'51″W, respectively, separated by approximately 650 km) within Manitoba to current (summer highs of 20-23°C) and future projected (+2-3°C) environmental temperatures of 16, 20 and 24°C for 30 days, and we measured gill transcriptional responses using RNAseq. Transcripts revealed SNPs consistent with genetically distinct populations and transcriptional responses altered by acclimation temperature. There were a higher number of differentially expressed transcripts observed in the southern, compared to the northern, population as temperatures increased, indicating enhanced transcriptional plasticity. Both lake sturgeon populations responded to elevated acclimation temperatures by downregulating the transcription of genes involved in protein synthesis and energy production. Furthermore, there were population-specific thresholds for the downregulation of processes promoting transcriptional plasticity as well as mitochondrial function as the northern population showed decreases at 20°C, while this capacity was not diminished until 24°C in the southern population. These transcriptional responses highlight the molecular impacts of increasing temperatures for divergent lake sturgeon populations during vulnerable developmental periods and the critical influence of transcriptome plasticity on acclimation capacity.

Exploring first-feeding diets for European eel larval culture: Insights at morphological, nutritional, and molecular levels.

Closing the life cycle of European eel (Anguilla anguilla) in captivity is targeted to provide a sustainable, year-round supply of juveniles for aquaculture. Present focus is on the nutritional requirements during the larval first-feeding period. In this study, three experimental diets were tested on hatchery-produced European eel larvae from the onset of the first-feeding stage commencing 10 days post hatch (dph) until 28 dph. Larval mortality was recorded daily, while sampling was conducted at regular intervals to record larval biometrics and analyze the expression of genes related to digestion, appetite, feed intake and growth. Two periods of high mortality were identified: the first appeared shortly after introduction of feeds (10-12 dph), while the second occurred 20-24 dph, indicating the "point of no return". This interpretation was supported at the molecular level by the expression of the gene encoding the "hunger hormone" ghrelin (ghrl) that peaked at 22 dph in all dietary trials, suggesting that most larvae were fasting. However, in larvae fed diet 3, ghrl expression was downregulated beyond 22 dph, which indicated that those larvae were no longer starving at this stage, while upregulation of genes encoding the major digestive enzymes (try, tgl, and amyl2a) advocated their healthy development. Moreover, for larvae fed diet 3, the expression of those genes as well as genes for feed intake (pomca) and growth (gh) continued to increase towards 28 dph. These results together with the registered highest survival, largest dry weight increase, and enhanced biometrics (length and body area) pointed to diet 3 as the best-performing. As a whole, this first-feeding study represents a landmark being the first to document European eel larval growth and survival beyond the point of no return, providing novel insights into the molecular development of digestive functions during the first feeding stage.

COVID-19 mortality increases with urbanization, but social distancing was largely ineffective in reducing deaths in Brazil and most parts of the World

Our aim is to assess how environmental and social variables are associated with COVID-19 mortality among countries and in the first and second waves among Brazilian states. We show that social isolation was not significantly, or was positively associated with COVID-19 mortality, which probably reflects people staying at home in the high mortality periods. The magnitude of temperature effects in Brazil varied depending on whether or not Index of Human Development was included in the regression analyses, but higher temperatures consistently reduced per capita deaths among countries. Availability of hospital bed capacity or intensive-care units had no detectable effect on mortality among countries, and within Brazil there was a positive relationship with excess deaths and a negative relationship with deaths per case during the second wave. Counterintuitively, mean age was negatively associated with deaths among Brazilian states, but was positively associated with mortality among countries. Mortality tended to be higher in states and countries with greater urbanization. Overall, the relationships of mortality-curve flatness, social isolation, temperature and hospital infrastructure with COVID-19 mortality were much weaker than is often assumed or are opposite in sign to the predictions, indicating that more complex models are needed to confront future epidemics.

Shifting Feeding Habits During Settlement Among Small Yellow Croakers (Larimichthys polyactis)

The small yellow croaker, Larimichthys polyactis, is a keystone species in the Yellow Sea and the East China Sea, with significant impacts on the regional ecosystem, but has experienced decades of population decline as a result of environmental changes and overfishing. The settlement of post-larval L. polyactis is a period of high mortality, with impacts on population recruitment and survival. This study examines the feeding habits of 49 post-larval and early juvenile L. polyactis in the Yangtze River estuary, in order to reveal diet composition before and after the settlement period. DNA barcoding methods (MiSeq and TA cloning) were used to examine gastrointestinal contents in detail. Both methods revealed that dietary breadth increased with increasing body length, while the dominance of copepods in the diet decreased as the body length increased. Post-larva (body length < 17 mm in this study) primarily fed on copepods. At the beginning of settlement (body length between 17 and 19 mm), L. polyactis began to ingest larger organisms, such as fishes and mysids, along with copepods. Larger early juveniles (body length > 20 mm) demonstrated a much wider dietary breadth, implying that successful settlement had occurred. Diet species richness in the MiSeq group was significantly greater than species richness in the TA cloning group, making the trend more pronounced within the MiSeq group. This indicates that the MiSeq method was more efficient than TA cloning in this study. We recommend that future research to investigate the feeding habits of fish larvae should combine MiSeq and visual examination methods.

Diel at‐sea activity of two species of great albatrosses: the ontogeny of foraging and movement behaviour

The first year of life is a period of high mortality in animals. Reduced foraging capacities of naive individuals might be the primary cause of their mortality. These capacities are supposed to be progressively acquired during the first months of life. In this study, we investigate the ontogeny of flight capacities, by day and night, of first‐year individuals, and compare it with adults from two closely related species of great albatrosses: Amsterdam Diomedea amsterdamensis and wandering Diomedea exulans albatrosses which forage in different environmental conditions. We used 71 tracks of 71 juvenile birds and 141 of 116 incubating adults to compare both age categories. In order to explore the effect of moon light on night activity, we elaborated a new formula which improves the precision of the proxy of moon illumination. By day, we found that juveniles of both species reach some adult foraging capacities in less than two months. By night, albatrosses have reduced activity increasing during the first weeks at sea for juveniles and changing in accordance with moon illumination for both juveniles and adults. A peak of flight activity at dawn and dusk was apparent for both species. Interspecific comparison underlined that Amsterdam albatrosses were more active than wandering albatrosses, suggesting a difference in food and foraging strategy. Overall, we highlighted how life history traits, environmental conditions and time of the day affect the foraging activity of two related species of seabirds.

Development of flight and foraging behaviour in a juvenile seabird with extreme soaring capacities.

The early life of animals is a period of high mortality, when foraging capacities are assumed to be improved progressively. In birds, this critical period involves the improvement of the flight. How do young birds gain these capacities has rarely been studied in natural conditions especially in seabirds that spend most of their life at sea. We used detailed GPS and body acceleration data on 37 great frigatebirds (Fregata minor), to test the hypothesis that juveniles starting their first flights have lower flying capacities than adults, but that these capacities will improve during a long learning period, before independence from parents, specific to this seabird that can spend months on the wing at sea. We found that most flight components improved over time to tend towards those of adults, especially the travel speed, range, duration and maximum altitude of trips. However, unexpectedly, juveniles had higher ascent rates, soaring and gliding capacities above the sea than adults. Moreover, energy expenditure of juveniles was similar to adults during low cost travelling movements and during active foraging, but juveniles spent more time foraging actively than adults. Our results suggest that flight tactics based on long-distance effortless movements specific to this family are acquired during a long period, but soaring and gliding capacities are already inherited by juveniles and possibly favoured by morphological adaptations specific to juveniles. These adaptations might explain the extreme dispersive capacities of juveniles.

Natural Regeneration Dynamics of Mora paraensis (Ducke) Ducke in Estuarine Floodplain Forests of the Amazon River

The aim of this study was to evaluate the natural regeneration dynamics of Mora paraensis in floodplain forests in three regions of the eastern Amazon, and specifically, to explore the relationship between the abundance of regenerating trees and canopy openness. Tree height and circumference of all individuals of height >50 cm and diameter at breast height (DBH) <5 cm were measured in 2012, 2013 and 2015. A matrix of transitions was created and the natural regeneration (RR), demographic and dynamic rates were calculated. Hemispherical photos were used to measure canopy openness. There was no difference in the density of regenerating trees between the three study regions (mean = 2.957 ind. ha−1). The abundance of regenerating trees was highest in 2013, when 5614 individuals were inventoried, and as such the RR 2012–2013 was positive in all three regions (mean = 7.9%). Between 2013 and 2015, the RR was negative and above 50% in all regions. Canopy openness had no significant effect on the abundance of regenerating trees. The abundance of regenerating trees of M. paraensis was high in estuarine floodplain forests of the Amazon River, but the regeneration dynamics varied between years with more favourable years alternating with periods of high mortality and negative regeneration.

Biological studies of Agalliana ensigera (Hemiptera: Cicadellidae), a leafhopper associated with several crop diseases in South America

Agalliana ensigera Oman (Cicadellidae: Megophthalminae) occurs frequently in several crops and has been involved in the epidemiology, or at least mentioned, as a vector of several diseases. Its biology was unknown and its nymphs had not yet been described. Here, we provide information on behavioral and biological parameters including descriptions of its immature stages. A. ensigera was able to complete its entire life cycle on alfalfa. Eggs were laid individually beneath the epidermis, in the stem internodes, in either mature or young tissues. Females had a pre-ovipositional period of around 5 days, and the average duration of the egg stage was 11 days. The nymphal period ranged 14–31 days, with an average of 22 days. A period of high mortality was recognized from emergence to day 10. Adult longevity averaged 16.5 days, but some individuals survived up to 96 days. The sex ratio was about 1.2:1 females to males. Females lived longer than males. Data on behavior and new distributional records and host plants are also provided.

Retrospective Analysis of Seasonal Ocean Growth Rates of Two Sea Winter Atlantic Salmon in Eastern Maine Using Historic Scales

AbstractSubstantial declines of anadromous Atlantic Salmon Salmo salar have occurred throughout its range, with many populations at the southern extent of the distribution currently extirpated or endangered. While both one sea winter (1SW) and two sea winter (2SW) spawner numbers for the North American stocks have declined since the 1950s, the decline has been most severe in 2SW spawners. The first months at sea are considered a period of high mortality. However, early ocean mortality alone cannot explain the more pronounced decline of 2SW spawners, suggesting that the second year at sea may be more critical than previously thought. Atlantic Salmon scales collected by anglers and the state agency from 1946 to 2013 from five rivers in eastern Maine were used to estimate smolt age and ocean age of returning adults. Additionally, seasonal growth rates of maiden 2SW spawners were estimated using intercirculi measurements and linear back-calculation methods. Generalized linear mixed models (Gaussian family, lo...

The Effects of Live and Artificial Diets on Feeding Performance of Winter Flounder, Pseudopleuronectes americanus, in the Hatchery

AbstractWinter flounder, Pseudopleuronectes americanus, are capable of releasing hundreds of thousands of eggs annually, but because of the vulnerability of the small, early life stages, there is high natural mortality, and few survive to maturity. Captively spawning, rearing, and releasing animals at a size or age beyond this period of high mortality may enhance stocks. The objectives of this research were to determine how different diets (both live and formulated) influenced hatchery survival and growth of juvenile winter flounder. Live feeds included post‐nauplii of brine shrimp, Artemia salina; white worms, Enchytraeus albidus; and common burrower amphipods, Leptocheirus plumulosus. Fish reared on live feeds exhibited significantly higher survival (P < 0.0001) and growth (P < 0.01) than those reared on formulated feed, with fish fed white worms exhibiting the highest growth rates. This study provides hatchery feeding strategies that may ease the transition of flatfish released into the wild for stock enhancement.

First Biological Data ofCeresa nigripectus(Hemiptera: Membracidae), a Common Treehopper on Alfalfa Crops in Argentina

Alfalfa (Medicago sativa L.; Fabaceae) is essential for argentinean agricultural develop- ment, but diseases like witchesbroom», caused by the ArAWB phytoplasma, are limiting factors for the production of this crop. Insects that visit alfalfa have been poorly studied. The treehopper, Ceresa nigripectus Remes Lenicov (Hemiptera: Membracidae) is very fre- quent in alfalfa crops; ArAWB was detected in several individuals of this treehopper, but the ability of this species to transmit the pathogen has not yet been demonstrated. The Membracidae family is a poorly studied group in Argentina. No data on the biology of C. nigripectus are available, and therefore the aim of this contribution is to provide information on its behavioral and biological parameters as a first step toward its control. The studies were conducted in the laboratory under controlled conditions. Ceresa nigripectus popula- tions were maintained on healthy alfalfa plants; the treehoppers were checked daily, the occurrence of molts was noted, and diverse aspects of nymphal and adult behavior were also recorded. A life table was built combining the observational data from 7 cohorts. Oviposi- tion sites were characterized by dissecting plants and through staining methods. Ceresa nigripectus could complete its life cycle entirely by using only alfalfa as a host. Females do not tend their broods. Eggs are laid individually and rarely 2 or 3 were found in the same slit. Eggs were located in the stems, in the nodes (in the axils of the leaves) or in the internodal space, between the epidermis and cortical tissues. The pre-ovipositional period was about 6 days, and the average duration of the egg stage was 20 days. The duration of nymphal period was variable, between 32 to 63 days, with a mean of 45 days. Two periods of high mortality were recognized, i.e., in the first instar, and during the second week of the adult stage. Longevity of adults averaged 61 days, but some individuals survived up to 202 days; females lived longer than males. In laboratory colonies, the sex ratio was about 1.3:1 females:males. All the developmental stages of the treehopper were tended by the ant Camponotus punctulatus Mayr. Data regarding behavioral aspects and new distributional information are also provided.

The ash dieback crisis: genetic variation in resistance can prove a long‐term solution

Over the last two decades, ash dieback has become a major problem inEurope, where the causative fungus has invaded the continent rapidly. The disease is caused by the invasive pathogenic fungusHymenoscyphus pseudoalbidus(anamorphChalara fraxinea), which causes severe symptoms and dieback in common ash,Fraxinus excelsior. It is becoming a significant threat to biodiversity in forest ecosystems and the economic and aesthetic impacts are immense. Despite the presence of the disease for at least 10 years inScandinavia, a small fraction ofF. excelsiortrees have remained vigorous, and these trees exhibit no or low levels of symptoms even where neighbouring trees are very sick. This gives hope that a fraction of the ash trees will retain a sufficiently viable growth to survive. Following a period of high mortality in natural populations, selection and breeding of remaining viable ash trees could therefore provide a route for restoring the role of ash in the landscape. This paper reviews the available data on disease dissemination, and the consequences thereof in terms of symptom severity and mortality, and appraises studies that have tested the hypothesis that less‐affected trees have genetically based resistance. The implications of the results for the adaptive potential of common ash to respond to the disease through natural or assisted selection are discussed. The risks of adverse fitness effects of population fragmentation due to high mortality are considered. Finally, it is recommended that resistant trees (genotypes) should be selected to facilitate conservation of the species.

Evidence for bluegill spawning plasticity obtained by disentangling complex factors related to recruitment

Fishes can exhibit many forms of plasticity to maximize fitness. However, limited information exists on the ability of freshwater fish to adjust spawning behavior and characteristics (e.g., timing, duration, magnitude of spawning events) to minimize mortality of recruits and ultimately maximize fitness. We wanted to test the life history hypothesis for bluegill (Lepomis macrochirus) (i.e., opportunistic strategy) utilizing existing literature and results from our study to further evaluate the potential for spawning plasticity in this species. Our objective was to identify bluegill recruitment bottlenecks (i.e., periods of high mortality) and factors associated with these events in a single lake during 7 consecutive years. Bluegills exhibited shorter spawning durations and fewer spawning pulses (i.e., peaks in larval production) compared with bluegill in previous studies. Late-hatched (compared with early-hatched) bluegills consistently contributed the most to the fall juvenile population; these recruitment patterns were primarily attributed to biotic drivers. Our study suggests that bluegill could exhibit spawning plasticity and extends our current understanding of adaptations that are potentially capable of increasing fitness for a freshwater fish species under a wide range of environmental conditions and uncertainty.

HEMATOLOGIC, PLASMA BIOCHEMISTRY, AND SELECT NUTRIENT VALUES IN CAPTIVE SMOOTH DOGFISH (MUSTELUS CANIS)

The Indianapolis Zoo maintains a large collection of smooth dogfish (Mustelus canis). During the first several years of captivity, there was a period of high mortality in adult, wild-caught sharks in the collection. Smooth dogfish with superficial abrasions would rapidly succumb to infection and death, regardless of the treatment approach. Although the sharks did successfully produce viable offspring, there was an elevated pup mortality rate, with 0% of the pups reaching 1 yr of age during the same period of high mortality in adult sharks. This poor response to captivity prompted interest in the physiologic response of these animals to illness. The objective of this investigation was to establish a preliminary data set of hematologic and plasma chemistry reference intervals, along with select nutrient parameters specific to wild-caught adults maintained in prolonged captivity (i.e., greater than 22 mo). Blood samples were collected from 20 clinically healthy, male (n = 10) and female (n = 10) dogfish sharks at the Oceans facility at the Indianapolis Zoo. Although gender differences in mortality rate were not apparent, complete blood cell counts, plasma biochemical profiles, and select nutrient analyses were performed and analyzed accordingly. Statistically significant differences (P < or = 0.05) specific to sex were determined for parameters including packed cell volume (PCV), absolute and relative fine eosinophilic granulocytes, relative percentage of coarse eosinophilic granulocytes, globulins, the albumin/globulin ratio, total protein, phosphorus, iron, selenium and copper. White blood cell counts appear to be lower in this species compared to other captive elasmobranchs. Further research into appropriate hematology standards including nutritional parameters appears warranted.

Anuran road-kills neighboring a peri-urban reserve in the Atlantic Forest, Brazil

Mortality from road-kills may figure among the important causes of decline in amphibian populations and species extinctions worldwide. Evaluation of the magnitude, composition, and temporal and spatial distributions of amphibian road-kills is a key step for mitigation planning, especially in peri-urban reserves. Once a month for 16 months, we surveyed, on foot, a 4.4 km section of state road ERS-389 bordering the Itapeva reserve in the southern Atlantic Forest. We recorded 1433 anuran road-kills and estimated a mortality rate of 9002 road-kills/km/year. The species most often recorded were the largest ones: Leptodactylus latrans, Rhinella icterica, Leptodactylus gracilis and Hypsiboas faber; 54.5% of the carcasses could not be identified. Anuran mortality was concentrated in summer, and was associated with temperature, rainfall and photoperiod. Leptodactylus road-kills were strongly influenced by vehicle traffic, probably because of its high abundance during the entire study period. Road-kill hotspots differed for anurans as a group and for single species, and we found an association among spatial patterns of mortality and types of land cover, distance from the nearest waterbody, roadside ditches, and artificial light. Traffic should be banned temporarily during periods of high mortality, which can be forecasted based on meteorological data. A comprehensive mitigation approach should take into account hotspots of all anuran records, and also of target species for selecting locations for amphibian passages and fencing. Roadside ditches, artificial waterbodies, and conventional street lights should be reduced as much as possible, since they may represent ecological traps for anuran populations.

Different pathways in the larval development of the crab Ucides cordatus (Decapoda, Ocypodidae) and their relation with high mortality rates by the end of massive larvicultures

One of the most limiting factors affecting the larval rearing of Ucides cordatus in the laboratory is a period of high mortality, which usually occurs late in the course of the larviculture during the metamorphosis from the zoeal to the megalopal phase. The objective of the present research was to analyze the post-embryonic development of U. cordatus on an individual basis and, in particular, to search for patterns linking disturbances in the molting process to the high larval death rates observed in massive larvicultures. A total of 50 larvae were individually reared from hatching to metamorphosis into the megalopal phase under controlled conditions, fed a combination of microalgae and rotifers. The survivorship rate was 70% until zoea V. The 35 surviving zoea V larvae followed two different pathways. Eleven underwent metamorphosis directly to megalopa, eighteen molted to zoea VI and six died as zoea V. In the last molting event, only two zoea VI larvae reached the megalopal stage, while the remaining sixteen died. In further observation under microscope, 13 of the dead zoea VI showed characteristics of the pre-molt stage and pereiopods disproportionably large in relation to the carapace. The observed pattern resembles the Molt Death Syndrome (MDS) described for other decapod species, in which larvae die in the late pre-molt phase of the molting cycle. We suggest that U. cordatus larvae develop disturbances in the molting process similar to the MDS described for other species and that these disturbances are related to a more complex pathway involving the emergence of larval stage zoea VI.

Stature, Mortality, and Life History among Indigenous Populations of the Andaman Islands, 1871–1986

Despite considerable interest in the evolution of small body size, there is little evidence for changes in body size within small‐bodied human populations. This study combines anthropometric data from a number of studies of the body size of Andaman Islanders from 1871 to 1986. The colonial history of the Andaman Islands is characterized by high rates of mortality among the indigenous populations. However, long‐term conflicts between tribal groups of the Andaman Islands and British and Indian settlers led to some groups being relatively isolated and sheltered from infectious disease and the high rates of mortality that affected other groups. When temporal trends in stature are compared in this context, there is evidence for a reduction in stature among the Great Andamanese who had close contact with the British during the period of highest mortality. Adult stature among the Onge appears to have increased as government involvement diminished following Indian independence. The Jarawa, who had lower rates of ...

Spacing patterns of an Acacia tree in the Kalahari over a 61-year period: How clumped becomes regular and vice versa

Nearest tree neighbour distances and the tree spatial formation on a large scale over time and space replicates were examined. The study was conducted in a natural savanna ecosystem in the Southern Kalahari, South Africa. Nearest tree neighbour and point pattern analysis methods were used to investigate changes in the spatial pattern of trees in two plots. Trees larger than 2 m canopy diameter were mapped. We used aerial photographs of the study area from 1940, 1964, 1984, 1993, and a satellite image from 2001 to follow two plots over time. Field work was carried out too for classification accuracy. We were able to identify and individually follow over 2400 individual trees from 1940 until 2001. Nearest neighbour analysis results indicate that dead trees were on average closer to their nearest neighbouring trees than living trees were to their neighbours. Most dead trees were on average 6 m from their nearest neighbours, while most living trees were about 20 m apart. Point pattern analysis results show a cyclical transition from clumped to random and sequentially to regular tree spacing. These transitions were not correlated across two plots. Generally, decreases in small-scale clumping coincided with periods of high mortality. Our findings show that regular, clumped, and random tree pattern can occur, pending on time, location, and scale within the location.