Forager Populations Research Articles

Forage Height and Above-Ground Biomass Estimation by Comparing UAV-Based Multispectral and RGB Imagery.

Crop height and biomass are the two important phenotyping traits to screen forage population types at local and regional scales. This study aims to compare the performances of multispectral and RGB sensors onboard drones for quantitative retrievals of forage crop height and biomass at very high resolution. We acquired the unmanned aerial vehicle (UAV) multispectral images (MSIs) at 1.67 cm spatial resolution and visible data (RGB) at 0.31 cm resolution and measured the forage height and above-ground biomass over the alfalfa (Medicago sativa L.) breeding trials in the Canadian Prairies. (1) For height estimation, the digital surface model (DSM) and digital terrain model (DTM) were extracted from MSI and RGB data, respectively. As the resolution of the DTM is five times less than that of the DSM, we applied an aggregation algorithm to the DSM to constrain the same spatial resolution between DSM and DTM. The difference between DSM and DTM was computed as the canopy height model (CHM), which was at 8.35 cm and 1.55 cm for MSI and RGB data, respectively. (2) For biomass estimation, the normalized difference vegetation index (NDVI) from MSI data and excess green (ExG) index from RGB data were analyzed and regressed in terms of ground measurements, leading to empirical models. The results indicate better performance of MSI for above-ground biomass (AGB) retrievals at 1.67 cm resolution and better performance of RGB data for canopy height retrievals at 1.55 cm. Although the retrieved height was well correlated with the ground measurements, a significant underestimation was observed. Thus, we developed a bias correction function to match the retrieval with the ground measurements. This study provides insight into the optimal selection of sensor for specific targeted vegetation growth traits in a forage crop.

Episodic-like memory in wild free-living blue tits and great tits

Episodic-like memory in non-human animals represents the behavioral characteristics of human episodic memory-the ability to mentally travel backward in time to "re-live" past experiences. A focus on traditional model species of episodic-like memory may overlook taxa possessing this cognitive ability and consequently its evolution across species. Experiments conducted in the wild have the potential to broaden the scope of episodic-like memory research under the natural conditions in which they evolved. We combine two distinct yet complementary episodic-like memory tasks (the what-where-when memory and incidental encoding paradigms), each targeting a different aspect of human episodic memory, namely the content (what-where-when) and process (incidental encoding), to comprehensively test the memory abilities of wild, free-living, non-caching blue tits (Cyanistes caeruleus) and great tits (Parus major). Automated feeders with custom-built programs allowed for experimental manipulation of spatiotemporal experiences on an individual-level basis. In the what-where-when memory experiment, after learning individualized temporal feeder rules, the birds demonstrated their ability to recall the "what" (food type), "where" (feeder location), and "when" (time since their initial visit of the day) of previous foraging experiences. In the incidental encoding experiment, the birds showed that they were able to encode and recall incidental spatial information regarding previous foraging experiences ("where" test), and juveniles, but not adults, were also able to recall incidentally encoded visual information ("which" test). Consequently, this study presents multiple lines of converging evidence for episodic-like memory in a wild population of generalist foragers, suggesting that episodic-like memory may be more taxonomically widespread than previously assumed.

Modeling terminal Pleistocene and Holocene forager population increase and environmental change in the Central Namib desert, Namibia

This paper examines the interplay of environmental change and human demographic shifts among late Pleistocene and Holocene populations in the hyper-arid context of the Central Namib Gravel plains, Western Namibia. This paper applies a structural equation modeling (SEM) approach to arid-zone hunter-gatherer mobility patterns and settlement systems based on variability among ethnographically and historically observed groups. It then applies this model in examining issues related to the Middle-to-Later Stone Age transition at the sites of Erb Tanks and the Mirabib rock shelter. This model suggests that, among modern arid-zone foragers, population density is by far the strongest factor influencing mobility and settlement systems, with higher population densities favoring longer residential site usages and shorter residential moves within smaller territories. In contrast, environmental variables having to do with annual rainfall, rainfall seasonality, and effective temperature affect mobility and settlement systems in ambiguous and statistically insignificant ways. This paper closes by arguing that regional-scale population increases signaled by various features of Later Stone Age archaeological patterning led to local population expansions in the Central Namib Desert, and that this in turn caused a range of recognizable cultural shifts that were strongly linked with adaptations to aridity.

Faecal bacterial communities differ amongst discrete foraging populations of dugongs along the east Australian coast.

Gut bacterial communities play a vital role in a host's digestion and fermentation of complex carbohydrates, absorption of nutrients, and energy harvest/storage. Dugongs are obligate seagrass grazers with an expanded hindgut and associated microbiome. Here, we characterised and compared the faecal bacterial communities of dugongs from genetically distinct populations along the east coast of Australia, between subtropical Moreton Bay and tropical Cleveland Bay. Amplicon sequencing of fresh dugong faecal samples (n=47) revealed Firmicutes (62%) dominating the faecal bacterial communities across all populations. Several bacterial genera (Bacteroides, Clostridium sensu stricto 1, Blautia and Polaribacter) were detected in samples from all locations, suggesting their importance in seagrass digestion. Principal coordinate analysis showed the three southern-most dugong populations having different faecal bacterial community compositions from northern populations. The relative abundances of the genera Clostridium sensu stricto 13 and dgA-11 gut group were higher, but Bacteroides was lower, in the southern dugong populations, compared to the northern populations, suggesting potential adaptive changes associated with location. This study contributes to our knowledge of the faecal bacterial communities of dugongs inhabiting Australian coastal waters. Future studies of diet selection in relation to seagrass availability throughout the dugong's range will help to advance our understanding of the roles that seagrass species may play in affecting the dugong's faecal bacterial community composition.

Women's subsistence networks scaffold cultural transmission among BaYaka foragers in the Congo Basin.

In hunter-gatherer societies, women's subsistence activities are crucial for food provisioning and children's social learning but are understudied relative to men's activities. To understand the structure of women's foraging networks, we present 230 days of focal-follow data in a BaYaka community. To analyze these data, we develop a stochastic blockmodel for repeat observations with uneven sampling. We find that women's subsistence networks are characterized by cooperation between kin, gender homophily, and mixed age-group composition. During early childhood, individuals preferentially coforage with adult kin, but those in middle childhood and adolescence are likely to coforage with nonkin peers, providing opportunities for horizontal learning. By quantifying the probability of coforaging ties across age classes and relatedness levels, our findings provide insights into the scope for social learning during women's subsistence activities in a real-world foraging population and provide ground-truth values for key parameters used in formal models of cumulative culture.

Factors influencing cranial variation between prehistoric Japanese forager populations

Understanding the factors shaping human crania has long been a goal of biological anthropology, and climate, diet, and population history are three of the most well-established influences. The effects of these factors are, however, rarely compared within a single, variable population, limiting interpretations of their relative contribution to craniofacial form. Jomon prehistoric foragers inhabited Japan throughout its climatic and ecological range and developed correspondingly varied modes of subsistence. We have previously demonstrated that a large sample of Jomon crania showed no clear climatic pattern; here, we examine variation in Jomon crania in more detail to determine if dietary factors and/or population history influence human intrapopulation variation at this scale. Based on well-established archaeological differences, we divide the Jomon into dietary groups and use geometric morphometric methods to analyse relationships between cranial shape, diet, and population history. We find evidence for diet-related influences on the shape of the neurocranium, particularly in the temporalis region. These shape differences may be interpreted in the context of regional variation in the biomechanical requirements of different diets. More experimental biomechanical and nutritional evidence is needed, however, to move suggested links between dietary content and cranial shape from plausible to well-supported. In contrast with the global scale of human variation, where neutral processes are the strongest influence on cranial shape, we find no pattern of population history amongst individuals from these Jomon sites. The determinants of cranial morphology are complex and the effect of diet is likely mediated by factors including sex, social factors, and chronology. Our results underline the subtlety of the effects of dietary variation beyond the forager/farmer dichotomy on cranial morphology and contribute to our understanding of the complexity of selective pressures shaping human phenotypes on different geographic scales.

Foraging and the importance of knowledge in Pemba, Tanzania: implications for childhood evolution.

Childhood is a period of life unique to humans. Childhood may have evolved through the need to acquire knowledge and subsistence skills. In an effort to understand the functional significance of childhood, previous research examined increases with age in returns to foraging across food resources. Such increases could be due to changes in knowledge, or other factors such as body size or strength. Here, we attempt to unpack these age-related changes. First, we estimate age-specific foraging returns for two resources. We then develop nonlinear structural equation models to evaluate the relative importance of ecological knowledge, grip strength and height in a population of part-time children foragers on Pemba island, Tanzania. We use anthropometric measures (height, strength, n = 250), estimates of ecological knowledge (n = 93) and behavioural observations for 63 individuals across 370 foraging trips. We find slower increases in foraging returns with age for trap hunting than for shellfish collection. We do not detect any effect of individual knowledge on foraging returns, potentially linked to information sharing within foraging parties. Producing accurate estimates of the distinct contribution of specific traits to an individual's foraging performance constitutes a key step in evaluating different hypotheses for the emergence of childhood.

Inter-household transfers of material goods among Sama "sea nomads" of the Philippines: Reciprocity, helping, signaling, or something else?

The extent to which humans share with both kin and non-kin is a defining characteristic of our species. Evolutionary research suggests that pervasive reliance on inter-individual transfers of goods and services may have evolved to support a cooperative breeding adaptation in humans. However, while intensive food sharing between individuals and families has frequently been investigated in small-scale human societies, a comprehensive analysis of the daily transfers of all material goods has not been attempted. Likewise, while much previous research on cooperative transfers focused on terrestrial foraging populations, less attention is paid to other small-scale economic modalities traditionally inhabited by humans. Drawing on over three years' worth of interviews and observational data from a community of primarily ethnic Sama people residing along the coast of Southern Mindanao Island in the Philippines, this paper examines the overall transfer patterns of material goods in a marine foraging economy. A quantitative description of resource acquisition is followed by an in-depth exploration of the characteristics of individual households and household dyads who gave and/or received more during the study period. Results indicate that a household's age and income are consistently correlated with increased inflow and outflow of material goods. Results also suggest differential motivations underlie inter-household sharing of food, money, and other goods in the study community. Most importantly, we find that both daily and long-term reciprocity overwhelmingly drive sharing within household dyads in the study community, despite secondary effects of kinship, relative need, and relative household age between household dyads.

Analysis of leaf forage value and screening of different populations of Pteroceltis tatarinowii, a rare and endemic species in China.

To fully exploit the economic value of the Chinese endemic species Pteroceltis tatarinowii and provide new resources for forage production, the forage nutritional value of P. tatarinowii leaves from different populations was analyzed and evaluated. The results were as follows: 1) There were significant differences in the forage nutrient indices of leaves from different populations. The crude protein content was 10.77%-18.65%, with an average of 14.58%, and the SDJN population had the highest crude protein content. The average crude fat, crude fiber content was 7.62%; the average neutral detergent fiber content was 25.33%; and the average acid detergent fiber contents were 6.79%, 7.62%, 25.33%, and 17.52%, respectively. The average phosphorus and calcium content in the leaves was 0.785 g·kg-1 and 58.01 g·kg-1, respectively. The tannin content was much lower than the antifeedant standard, at an average of 4.97 g·kg-1. The average total amounts of hydrolyzed and free amino acids in the leaves were 108.20 mg·g-1 and 47.87 mg·g-1, respectively. Thus, P. tatarinowii leaves have high crude protein, crude fat, and calcium contents, and low fiber, tannin contents, and are protein-rich. These results provide evidence that this species can be developed into an excellent woody forage tree. 2) There were significant differences in the forage quality evaluation indices among the populations. The forage indices of NDP, ADP, DMI, DDM, and RFV of 21 populations all met the super standard of the American Grass and Grassland Association (AFGC) for hay, two crude protein indices met the grade 1 standard, and 12 crude protein indices met the grade 2 standard. Four high-protein and high-RFV forage populations (SDJN, SDZZ, SXLQ, and AHXX) were selected. 3) The results of the correlation analysis showed that there was no significant correlation between the forage characteristics of P. tatarinowii leaves and latitude and longitude, indicating no significant geographical variation. However, the forage characteristics were strongly correlated with elevation, average annual temperature, and annual precipitation. Thus, high elevation, low temperatures, and rainy weather can improve the forage value of the leaves. P. tatarinowii can be planted to provide leaf forage in cold and wet areas at a specific elevation. Moreover, the forage value of P. tatarinowii leaves can be further improved by increasing nitrogen fertilizer and reducing K and Ca fertilizers during cultivation. 4) Cluster analysis revealed obvious regionalism. Taking the Yangtze River Basin as the limit, cluster analysis divided the species into four population groups: the Yangtze River Basin and northern, southwestern, and eastern coastal populations.

The Myth of Man the Hunter: Women's contribution to the hunt across ethnographic contexts.

The sexual division of labor among human foraging populations has typically been recognized as involving males as hunters and females as gatherers. Recent archeological research has questioned this paradigm with evidence that females hunted (and went to war) throughout the Homo sapiens lineage, though many of these authors assert the pattern of women hunting may only have occurred in the past. The current project gleans data from across the ethnographic literature to investigate the prevalence of women hunting in foraging societies in more recent times. Evidence from the past one hundred years supports archaeological finds from the Holocene that women from a broad range of cultures intentionally hunt for subsistence. These results aim to shift the male-hunter female-gatherer paradigm to account for the significant role females have in hunting, thus dramatically shifting stereotypes of labor, as well as mobility.

Post-Traumatic Stress Disorder (PTSD) in San Forager Theories of Disease, and Its Implications for Understanding Images of Conflict in Southern African Rock Art

San forager populations in nineteenth-century southern Africa were forced to adapt to greatly destructive aspects of the colonial project. Forging new societies from heterogeneous sources, they engaged in prolonged armed insurgency, recording their exploits, presence and beliefs in the rock-art archive of the Maloti-Drakensberg. These images reference conflict and trauma, conventionally interpreted as visions of spiritual warfare. However, viewed through the lens of post-traumatic stress disorder (PTSD), deeper dimensions emerge. PTSD is the culturally subjective experience of generalizable neuropathologies which develop following a traumatic event. Diagnosable in diverse communities worldwide, it nonetheless requires insider idioms to understand its local expressions. We explore how PTSD manifested in this historic and cultural context; how its symptomatic social dysfunctions would have been understood in forager aetiology, and how its intrusive flashbacks would have intruded on altered-state experiences induced to heal the consequences of violence. We find that the artists were not passive victims of trauma, but rather used art symbolically to reconsolidate individual and collective understandings of traumatic events.

Pastoralism, hunting, and coexistence: Domesticated and wild bovids in Neolithic Sudan

AbstractThe interactions between mobile pastoralists and semi‐sedentary Nilotic foraging groups in the Middle Nile Valley had long‐term implications for the development of social complexity as seen in the ancient African kingdom of Kerma. This study presents the results of the zooarcheological analysis of animal remains from two sites in the 4th cataract of the Nile valley, El Ginefab and Shemkhiya, and compares findings to other published sites in the region during a period of significant climatic change. Results indicate that the communities living at Shemkhiya and El Ginefab differed in terms of their meat preferences and their primary modes of bovid acquisition, and that pastoralist practices changed at El Ginefab through time. Hunting remained an important feature of subsistence practices, and regional comparisons indicate that the acquisition of wild bovids did not disappear with incorporation of domesticated livestock; however, pastoralists limited their hunting practices to smaller wild bovids in contrast to neighboring forager populations. A clear chronological overlap is documented between communities reliant on pastoralism and those reliant on hunting as a subsistence practice for several millennia. This highlights the need to more explicitly characterize and understand the dynamics of coexistence for the spread and establishment of pastoralism regionally, as well as how social ties, subsistence practices, and land use practices overlapped during periods of critical environmental changes and their implications for emerging social complexity.

Associations between men's reputations for fathering and their reproductive success among BaYaka foragers in the Congo Basin

It is generally recognized that paternal care is a facultative feature of human cooperative caregiving that helps underpin our evolved life history strategy. Yet, little direct evidence links variation in men's fathering to fitness outcomes. Research in small-scale, subsistence-level societies has focused more on links between fitness and men's social status, which overlaps with paternal care (e.g., hunting prowess/reputation and provisioning) but is distinct. Helping address this gap, we demonstrate linkages between fathers' roles and fitness-related outcomes among the BaYaka, a highly egalitarian Congo Basin forager population. Using measures drawn from community perceptions of men's quality in locally-valued domains of fathering, we find that BaYaka men (N = 31) ranked as better at providing for their families and sharing resources with the community had more living children. We observed a similar pattern for men ranked as better teachers, though evidence from Bayesian regression models was weaker than for these other domains. Those men ranked higher for provisioning and sharing, respectively, also had more total children (living and deceased combined). These fathering qualities were not significantly associated with variation in child mortality. Our results are consistent with long-standing arguments around the evolutionary importance of provisioning as paternal care, and point to other pathways, such as resource sharing, through which higher quality paternal care can be linked to reproductive success.

Wealth, health and inequality in Agta foragers.

There is significant evidence from large-scale, industrial and post-industrial societies that greater income and wealth inequality is negatively associated with both population health and increasing health inequalities. However, whether such relationships are inevitable and should be expected to impact the health of small-scale societies as they become more market-integrated is less clear. Here, using mixed-effect models, we explore the relationship between health, wealth, wealth inequality and health inequalities in a small-scale foraging population from the Philippines, the Agta. Across 11 camps, we find small to moderate degrees of wealth inequality (maximal Gini Coefficient 0.44) which is highest in the most permanent camps, where individuals engage more heavily in the formal market. However, in both adults (n = 161) and children (n = 215), we find little evidence that either wealth or wealth inequality associates with ill health, except for one measure of nutritional condition-red blood cell count. We interpret these results in the light of high levels of cooperation among the Agta which may buffer against the detrimental effects of wealth inequality documented in industrial and post-industrial societies. We observe little intergenerational wealth transmission, highlighting the fluid nature of wealth, and thus wealth inequality, particularly in mobile communities. The deterioration of nutritional status, as indicated by red blood cell counts, requires further investigation before concluding the Agta's extensive cooperation networks may be beginning to breakdown in the face of increasing inequality.

Changes in limiting factors for forager population dynamics in Europe across the last glacial-interglacial transition

Population dynamics set the framework for human genetic and cultural evolution. For foragers, demographic and environmental changes correlate strongly, although the causal relations between different environmental variables and human responses through time and space likely varied. Building on the notion of limiting factors, namely that at any one time, the scarcest resource caps population size, we present a statistical approach to identify the dominant climatic constraints for hunter-gatherer population densities and then hindcast their changing dynamics in Europe for the period between 21,000 to 8000 years ago. Limiting factors shifted from temperature-related variables (effective temperature) during the Pleistocene to a regional mosaic of limiting factors in the Holocene dominated by temperature seasonality and annual precipitation. This spatiotemporal variation suggests that hunter-gatherers needed to overcome very different adaptive challenges in different parts of Europe and that these challenges varied over time. The signatures of these changing adaptations may be visible archaeologically. In addition, the spatial disaggregation of limiting factors from the Pleistocene to the Holocene coincided with and may partly explain the diversification of the cultural geography at this time.

Insectivorous bats form mobile sensory networks to optimize prey localization: The case of the common noctule bat

Animals that depend on ephemeral, patchily distributed prey often use public information to locate resource patches. The use of public information can lead to the aggregation of foragers at prey patches, a mechanism known as local enhancement. However, when ephemeral resources are distributed over large areas, foragers may also need to increase search efficiency, and thus apply social strategies when sampling the landscape. While sensory networks of visually oriented animals have already been confirmed, we lack an understanding of how acoustic eavesdropping adds to the formation of sensory networks. Here we radio-tracked a total of 81 aerial-hawking bats at very high spatiotemporal resolution during five sessions over 3 y, recording up to 19 individuals simultaneously. Analyses of interactive flight behavior provide conclusive evidence that bats form temporary mobile sensory networks by adjusting their movements to neighboring conspecifics while probing the airspace for prey. Complementary agent-based simulations confirmed that the observed movement patterns can lead to the formation of mobile sensory networks, and that bats located prey faster when networking than when relying only on local enhancement or searching solitarily. However, the benefit of networking diminished with decreasing group size. The combination of empirical analyses and simulations elucidates how animal groups use acoustic information to efficiently locate unpredictable and ephemeral food patches. Our results highlight that declining local populations of social foragers may thus suffer from Allee effects that increase the risk of collapses under global change scenarios, like insect decline and habitat degradation.

Success-biased social learning in a one-consumer, two-resource model

Previous analyses have predicted that social learning should not evolve in a predator–prey system. Here we examine whether success-biased social learning, by which social learners copy successful demonstrators, allows social learning by foragers to evolve. We construct a one-predator, two-prey system in which foragers must learn how to feed on depletable prey populations in an environment where foraging information can be difficult to obtain individually. We analyze two models in which social learning is success-biased: in the first, individual learning does not depend on the resource dynamics, and in the second model it depends on the relative frequency of the resource. Unlike previous results, we find that social learning does not cause predators to over-harvest one type of prey over the other. Furthermore, increasing the probability of social learning increases the probability of learning a successful foraging behavior, especially when individually learned information tends to be inaccurate. Whereas social learning does not evolve among individual learners in the first model, the assumption of resource-dependent learning in the second model allows a mutant with an increased probability of social learning to spread through the forager population.

The origins and practice of insect-foraging technology

Over the course of our evolution, humans have developed increasingly sophisticated technology for utilising natural resources. The origins of these technologies are difficult to identify since they rely on natural resources that are often perishable in local environments so do not preserve for archaeologists to find millions of years later. However, by looking at our closest cousin in the order Primates, we see that chimpanzees utilise tools, most commonly for foraging for social insects such as ants and termites. This parallel suggests that our early ancestors would have had a similar capacity for making and using tools, quite possibly for the same goal of extracting insects from their nests. By 1.5 million years ago, we see archaeological evidence of tools used for insect foraging in the form of bone digging implements. With the evolution of our genusHomo, the capacity to use forethought to create more complicated tools opens up the possibility for baskets and nets. These items do not preserve in very ancient sediments, but they begin to appear around 25,000 years ago, and their utility to contemporary foraging populations supports the notion of a more ancient origin. Each of these advances intensifies human utilisation of insects as a food resource and are precursor to more extensive environmental manipulation and eventual agriculture. As insect consumption scales up around the world today, it requires increasing intensification, but this is a challenge humans have been overcoming for millions of years.

Hominin forager technology, food sharing, and diet breadth

We propose a predator–prey model to explain diachronic changes in Palaeolithic diet breadth. The fraction of rapidly-reproducing hard-to-catch hares and birds among small animals in the hominin diet shows a significant increase between the Middle and Upper Palaeolithic in the Levant, with an associated decrease in slowly-reproducing easily-caught tortoises. Our model interprets this fraction in terms of foraging effort allocated to, and foraging efficiency for each of these two classes of resource, in addition to their abundances. We focus on evolutionary adjustments in the allocation of foraging effort. The convergence stable strategy (CSS) of foraging effort and the dietary fraction of hares/birds are both highly sensitive to variation in the foraging efficiencies, which may have been upgraded by advanced technology introduced from Africa or developed locally. A positive correlation (not necessarily a cause and effect relationship) is observed between this fraction and forager population when the foraging efficiency for hares/birds is varied. Overexploitation can however result in a reduction of both diet breadth and forager population, as can food sharing within the forager group. Food sharing is routine among recent (and perhaps also Palaeolithic) foragers. We speculate that some controversial issues regarding this public goods problem might be resolved if we could incorporate sexual selection into our model.

High-throughput single nucleotide polymorphism genotyping reveals population structure and genetic diversity of tall fescue (

Single nucleotide polymorphisms (SNPs) are the most abundant form of genetic variation in eukaryote genomes and may be useful for selection of genetically distant parents for crossing in breeding programs. In this study, genome-wide SNPs of tall fescue (Festuca arundinacea Schreb.) were genotyped by using double-digest restriction-site-associated DNA sequencing to determine the genetic variation and differentiation among and within forage, turf and hybrid populations. After filtering, 16 036 SNPs were used to investigate genetic diversity and for structure analysis. SNP markers clearly differentiated the populations from each other. However, the hybrid population had a higher genetic similarity with the turf population than with the forage population. The results were confirmed by genetic differentiation (fixation index, Fst) and gene flow (Nm) statistics, so that low Fst and high Nm were observed between turf and hybrid groups, indicating less genetic distance and a high similarity between them. Based on the results of the weighted pair group method with arithmetic mean clustering, discriminant analysis of principal components and analysis of molecular variance, greater genetic differentiations were found among diverse turf, forage and hybrid populations, especially between turf and forage ones. In conclusion, numerous informative SNPs, natural allelic diversity-led domestication patterns, basic genetic variation statistics (e.g. Fst and heterozygosity) and population structures have multidimensional applicability for tall fescue genomics-assisted breeding.