scholarly journals Seasonal dietary changes increase the abundances of savanna herbivore species

2020 ◽  
Vol 6 (40) ◽  
pp. eabd2848
Author(s):  
A. Carla Staver ◽  
Gareth P. Hempson
Keyword(s):  
Theoretical Models ◽  
Mixed Feeding ◽  
Population Declines ◽  
African Savanna ◽  
Historical Pattern ◽  
Population Sizes ◽  
Herbivore Species ◽  
Diet Shifts ◽  
Dietary Strategies ◽  
Mixed Feeder

African savannas are home to the world’s last great megafaunal communities, but despite ongoing population declines, we only poorly understand the constraints on savanna herbivore abundances. Seasonal diet shifts (except migration) have received little attention, despite a diversity of possible dietary strategies. Here, we first formulate two theoretical models that predict that both mixed feeding and migratory grazing increase population sizes. These predictions are borne out in comprehensive data across African savanna parks: Mixed feeders are the most abundant herbivores in Africa, alongside a few migratory grazer populations. Overall, clear mixed-feeder dominance may reflect a historical pattern or may instead mirror a general global decline in specialists. Regardless, mixed feeders dominate the savannas of the present and future.

scholarly journals Demographic inference provides insights into the extirpation and ecological dominance of eusocial snapping shrimps

2020 ◽  
Author(s):  
Solomon T. C. Chak ◽  
Stephen E. Harris ◽  
Kristin M. Hultgren ◽  
J. Emmett Duffy ◽  
Dustin R. Rubenstein
Keyword(s):  
Life Histories ◽  
Environmental Changes ◽  
Population Declines ◽  
Effective Population ◽  
Social Traits ◽  
Population Sizes ◽  
Demographic Inference ◽  
Ecological Dominance ◽  
Snapping Shrimps ◽  
Eusocial Species

AbstractEusocial animals often achieve ecological dominance in the ecosystems where they occur, a process that may be linked to their demography. That is, reproductive division of labor and high reproductive skew in eusocial species is predicted to result in more stable effective population sizes that may make groups more competitive, but also lower effective population sizes that may make groups more susceptible to inbreeding and extinction. We examined the relationship between demography and social organization in one of the few animal lineages where eusociality has evolved recently and repeatedly among close relatives, the Synalpheus snapping shrimps. Although eusocial species often dominate the reefs where they occur by outcompeting their non-eusocial relatives for access to sponge hosts, many eusocial species have recently become extirpated across the Caribbean. Coalescent-based historical demographic inference in 12 species found that across nearly 100,000 generations, eusocial species tended to have lower but more stable effective population sizes through time. Our results are consistent with the idea that stable population sizes may enable eusocial shrimps to be more competitively dominant, but they also suggest that recent population declines are likely caused by eusocial shrimps’ heightened sensitivity to anthropogenically-driven environmental changes as a result of their low effective population sizes and localized dispersal, rather than to natural cycles of inbreeding and extinction. Thus, although the unique life histories and demography of eusocial shrimps has likely contributed to their persistence and ecological dominance over evolutionary timescales, these social traits may also make them vulnerable to contemporary environmental change.

scholarly journals Coalescent models at small effective population sizes and population declines are positively misleading

2019 ◽  
Author(s):  
M. Elise Lauterbur
Keyword(s):  
Genetic Diversity ◽  
Sample Size ◽  
Population Size ◽  
Effective Population Size ◽  
Genetic Relationships ◽  
Population Decline ◽  
Population Declines ◽  
Effective Population ◽  
Analytical Approximations ◽  
Population Sizes

AbstractPopulation genetics employs two major models for conceptualizing genetic relationships among individuals – outcome-driven (coalescent) and process-driven (forward). These models are complementary, but the basic Kingman coalescent and its extensions make fundamental assumptions to allow analytical approximations: a constant effective population size much larger than the sample size. These make the probability of multiple coalescent events per generation negligible. Although these assumptions are often violated in species of conservation concern, conservation genetics often uses coalescent models of effective population sizes and trajectories in endangered species. Despite this, the effect of very small effective population sizes, and their interaction with bottlenecks and sample sizes, on such analyses of genetic diversity remains unexplored. Here, I use simulations to analyze the influence of small effective population size, population decline, and their relationship with sample size, on coalescent-based estimates of genetic diversity. Compared to forward process-based estimates, coalescent models significantly overestimate genetic diversity in oversampled populations with very small effective sizes. When sampled soon after a decline, coalescent models overestimate genetic diversity in small populations regardless of sample size. Such overestimates artificially inflate estimates of both bottleneck and population split times. For conservation applications with small effective population sizes, forward simulations that do not make population size assumptions are computationally tractable and should be considered instead of coalescent-based models. These findings underscore the importance of the theoretical basis of analytical techniques as applied to conservation questions.

scholarly journals Continent-wide effects of urbanization on bird and mammal genetic diversity

2019 ◽  
Author(s):  
C. Schmidt ◽  
M. Domaratzki ◽  
R.P. Kinnunen ◽  
J. Bowman ◽  
C.J. Garroway
Keyword(s):  
Genetic Diversity ◽  
Environmental Changes ◽  
Bird Species ◽  
Population Level ◽  
Natural Environments ◽  
Population Declines ◽  
Effective Population ◽  
Human Footprint ◽  
Rate Of Increase ◽  
Population Sizes

AbstractUrbanization and associated environmental changes are causing global declines in vertebrate populations. In general, population declines of the magnitudes now detected should lead to reduced effective population sizes for animals living in proximity to humans and disturbed lands. This is cause for concern because effective population sizes set the rate of genetic diversity loss due to genetic drift, the rate of increase in inbreeding, and the efficiency with which selection can act on beneficial alleles. We predicted that the effects of urbanization should decrease effective population size and genetic diversity, and increase population-level genetic differentiation. To test for such patterns, we repurposed and reanalyzed publicly archived genetic data sets for North American birds and mammals. After filtering, we had usable raw genotype data from 85 studies and 41,023 individuals, sampled from 1,008 locations spanning 41 mammal and 25 bird species. We used census-based urban-rural designations, human population density, and the Human Footprint Index as measures of urbanization and habitat disturbance. As predicted, mammals sampled in more disturbed environments had lower effective population sizes and genetic diversity, and were more genetically differentiated from those in more natural environments. There were no consistent relationships detectable for birds. This suggests that, in general, mammal populations living near humans may have less capacity to respond adaptively to further environmental changes, and be more likely to suffer from effects of inbreeding.

Differing influences of resource availability on the demographics and habitat selection of wildebeest compared with impala

2014 ◽  
Vol 30 (3) ◽  
pp. 189-198 ◽  
Author(s):  
Christopher A.J. O'Kane ◽  
Bruce R. Page ◽  
David W. Macdonald
Keyword(s):  
Habitat Selection ◽  
Fire Regimes ◽  
Perinatal Period ◽  
Dry Season ◽  
Annual Rainfall ◽  
Habitat Occupancy ◽  
Significant Relationships ◽  
Population Sizes ◽  
Mixed Feeder ◽  
Selection Of

Abstract:Although what drives the abundance and habitat selection of ungulates is a long-standing question, coherent datasets investigating the influences of rainfall, competition and fire on ungulates are unusual. Over 4 y we carried out extensive monthly road transects in Ithala Game Reserve, South Africa, to determine the demographics and habitat occupancy of the region's prevalent grazer (wildebeest) and mixed-feeder (impala). Habitat occupancy was determined using a GIS-based approach. We obtained 8742 sighting records, encompassing 8400 wildebeest and 10071 impala. Annual rainfall did not significantly correlate with population sizes of either species. Fecundity of wildebeest, but not of impala, showed a significant positive relationship with rainfall specifically over the perinatal period (November–December), whilst no significant relationships were found for either species between fecundity and rainfall over the previous year, 2 y, rut (February–April) or height of the dry season (June–August). Impala unexpectedly favoured browse habitats to grassland year round, probably consequent on competition for grass with wildebeest. Dry-season grass flushes attracted both wildebeest and impala. The study emphasized how rainfall, competition and fire regimes may affect differently grazers compared with mixed-feeders.

scholarly journals Dietary innovations spurred the diversification of ruminants during the Caenozoic

2014 ◽  
Vol 281 (1776) ◽  
pp. 20132746 ◽  
Author(s):  
Juan L. Cantalapiedra ◽  
Richard G. FitzJohn ◽  
Tyler S. Kuhn ◽  
Manuel Hernández Fernández ◽  
Daniel DeMiguel ◽  
...  
Keyword(s):  
Global Climate ◽  
Mixed Feeding ◽  
Evolutionary Transitions ◽  
Feeding Styles ◽  
Ecological Flexibility ◽  
Climate Shifts ◽  
Adaptive Radiations ◽  
Global Temperature Change ◽  
Major Factors ◽  
Mixed Feeder

Global climate shifts and ecological flexibility are two major factors that may affect rates of speciation and extinction across clades. Here, we connect past climate to changes in diet and diversification dynamics of ruminant mammals. Using novel versions of Multi-State Speciation and Extinction models, we explore the most likely scenarios for evolutionary transitions among diets in this clade and ask whether ruminant lineages with different feeding styles (browsing, grazing and mixed feeding) underwent differential rates of diversification concomitant with global temperature change. The best model of trait change had transitions from browsers to grazers via mixed feeding, with appreciable rates of transition to and from grazing and mixed feeding. Diversification rates in mixed-feeder and grazer lineages tracked the palaeotemperature curve, exhibiting higher rates during the Miocene thermal maxima. The origination of facultative mixed diet and grazing states may have triggered two adaptive radiations—one during the Oligocene–Miocene transition and the other during Middle-to-Late Miocene. Our estimate of mixed diets for basal lineages of both bovids and cervids is congruent with fossil evidence, while the reconstruction of browser ancestors for some impoverished clades—Giraffidae and Tragulidae—is not. Our results offer model-based neontological support to previous palaeontological findings and fossil-based hypothesis highlighting the importance of dietary innovations—especially mixed feeding—in the success of ruminants during the Neogene.

Dietary interpretation and paleoecology of herbivores from Pikermi and Samos (late Miocene of Greece)

Paleobiology ◽  
2010 ◽  
Vol 36 (1) ◽  
pp. 113-136 ◽  
Author(s):  
Nikos Solounias ◽  
Florent Rivals ◽  
Gina M. Semprebon
Keyword(s):  
Late Miocene ◽  
Central Africa ◽  
Individual Species ◽  
Mixed Feeding ◽  
African Savanna ◽  
African Species ◽  
Microwear Analysis ◽  
As Species ◽  
Colobine Monkey ◽  
Of Greece

A large sample of the Pikermi and Samos ungulates was examined by microwear analysis using a light stereomicroscope (561 extinct and 809 extant comparative specimens). The results were used to infer the dietary adaptations of individual species and to evaluate the Pikermian Biome ungulate fauna. Many of the bovids have wear consistent with mixed feeding, although a few mesodont taxa apparently enjoyed an exclusive browsing and or grazing diet. The giraffids spanned the entire dietary spectrum of browsing, mixed feeding, and grazing, but most of the three-toed horses (Hippotherium) were hypsodont grazers. The colobine monkey Mesopithecus pentelici displays microwear consistent with a mixed fruit and leaf diet most likely including some hard objects. Similar results were obtained from prior scanning electron microscopy microwear studies at 500 times magnification and from the light microscope method at 35 times magnification for the same species. Results show that diet can differ between species that have very similar gross tooth morphology. Our results also suggest that the Pikermian Biome was most likely a woodland mosaic that provided a diversity of opportunities for species that depended on browsing as well as species that ate grass. The grasses were most likely C3 grasses that would grow in shaded areas of the woodland, glades, and margins of water. The ungulate component of the Pikermi and Samos fauna was more species-rich and more diverse in diet than the ungulates observed in modern African forests, woodlands, or savannas, yet dietarily most similar to the ungulates found in woodland elements of India and to some extent of Africa. It is unlikely that the Pikermi and Samos ungulates inhabited dense forests because we find no evidence for heavy fruit browsing. Conversely, a pure savanna is unlikely because many mixed feeders are present as well as browsers. Extant woodland African species are morphologically and trophically very similar to the African savanna species. Therefore the evolution of grazing and of hypsodont morphology for Africa may have evolved within the Plio-Pleistocene woodlands of Africa. Our results show that major dietary and morphologic ungulate evolution may take place within woodlands rather than as a consequence of species moving into savannas both during the late Miocene of Pikermi and Samos and during the Pleistocene–Recent of Central Africa.

An experimental study of declining populations

2005 ◽  
Vol 32 (6) ◽  
pp. 481 ◽  
Author(s):  
Jim Hone ◽  
the late Graeme Caughley ◽  
David Grice
Keyword(s):  
Experimental Study ◽  
Population Decline ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Second Phase ◽  
Population Declines ◽  
Negative Effects ◽  
Instantaneous Rate ◽  
Rate Of Increase ◽  
Declining Populations

Wildlife population declines have been attributed to predation, habitat change, and other agents of decline. An experimental study applied predation (at three levels) and habitat (at two levels) treatments over two years and measured the patterns of decline of populations of a medium-sized mammal (European rabbits). A model of population dynamics and effects of the treatments predicted negative effects of both treatments and an interaction of the treatments. All populations declined during the study including the experimental controls. During the first seven months (first phase of the study) the rate of decline, as estimated by the observed monthly instantaneous rate of increase (r), was more negative (P < 0.05) with increasing predation levels but there was no effect (P > 0.05) of habitat manipulation on r. There were no significant effects of treatments on rabbit abundance, or density, during the first phase of the study. During the second phase of the study, of 12 months’ duration, there were no significant (P > 0.05) effects of treatments on rabbit abundance, density, or r. There were no significant (P > 0.05) interactions of treatments on any response variable during either phase of the study. The interaction predicted by the theoretical model was not supported. Estimated abundance at the end of the study was not related (P > 0.05) to initial abundance (correlation = 0.023). The implications of the results are that such experimental studies can be used to evaluate theoretical models, though such studies may require a larger number of treatment replicates, and treatments at more extreme levels, to more clearly detect the effects of agents of population decline and their interactions.

scholarly journals Climate change, not human population growth, correlates with Late Quaternary megafauna declines in North America

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mathew Stewart ◽  
W. Christopher Carleton ◽  
Huw S. Groucutt
Keyword(s):  
Climate Change ◽  
North America ◽  
North American ◽  
Human Population ◽  
Late Quaternary ◽  
Bayesian Regression ◽  
Population Declines ◽  
Radiocarbon Dates ◽  
Population Sizes ◽  
Do So

AbstractThe disappearance of many North American megafauna at the end of the Pleistocene is a contentious topic. While the proposed causes for megafaunal extinction are varied, most researchers fall into three broad camps emphasizing human overhunting, climate change, or some combination of the two. Understanding the cause of megafaunal extinctions requires the analysis of through-time relationships between climate change and megafauna and human population dynamics. To do so, many researchers have used summed probability density functions (SPDFs) as a proxy for through-time fluctuations in human and megafauna population sizes. SPDFs, however, conflate process variation with the chronological uncertainty inherent in radiocarbon dates. Recently, a new Bayesian regression technique was developed that overcomes this problem—Radiocarbon-dated Event-Count (REC) Modelling. Here we employ REC models to test whether declines in North American megafauna species could be best explained by climate changes, increases in human population densities, or both, using the largest available database of megafauna and human radiocarbon dates. Our results suggest that there is currently no evidence for a persistent through-time relationship between human and megafauna population levels in North America. There is, however, evidence that decreases in global temperature correlated with megafauna population declines.

New perspectives in vertebrate paleoecology from a recent bone assemblage

Paleobiology ◽  
1979 ◽  
Vol 5 (1) ◽  
pp. 12-21 ◽  
Author(s):  
Anna K. Behrensmeyer ◽  
David Western ◽  
Dorothy E. Dechant Boaz
Keyword(s):  
Land Surface ◽  
Census Data ◽  
Habitat Specificity ◽  
Extant Species ◽  
Modern Analogue ◽  
Final Mode ◽  
Population Sizes ◽  
Herbivore Species ◽  
Fossil Assemblages ◽  
Land Surfaces

Interpretations of vertebrate paleoecology depend on knowledge of taphonomical processes which alter the composition of the preserved fossil assemblage from that of the original community. Study of the potential fossil record of a recent mammal community in Amboseli National Park, Kenya, shows the effects of some of these biasing processes and demonstrates how a bone assemblage on a modern land surface can be a source of past and present ecological information. In the bone assemblage, species presence or absence and relative abundance differ from recorded living species occurrences and population sizes: only 74% of the extant species in the basin are identified in the bone sample, and carcass abundances vary significantly from known population sizes of the major herbivore species. Both biases appear to be strongly correlated to body size, and this results from greater destruction of bones of smaller animals within the weight range from about 1-1000 kg. This size-biasing against small species appears to be due primarily to the greater susceptibility of small bones to destruction by carnivore mastication, breakage through bioturbation (trampling), and physical and chemical processes of weathering. Size-biasing resulting from such primary processes can thus be inherited by buried bone assemblages whatever their final mode of deposition. The bone assemblage also provides information on the spatial distributions of the major herbivore species over six major habitats. Patterns of strong habitat specificity are accurately represented in the bone assemblage. However, the record for certain species is affected by their seasonal and diurnal habitat shifts so that their bone distributions do not match live census data. The Amboseli bone assemblage provides a modern analogue for taphonomical processes which may have affected fossil assemblages derived from paleo-land surfaces prior to fluvial transport. It also helps to define limits of resolution in interpreting paleoecological information from such fossil assemblages.

scholarly journals Resolving the impact of waiting time distributions on the persistence of measles

2009 ◽  
Vol 7 (45) ◽  
pp. 623-640 ◽  
Author(s):  
Andrew J. K. Conlan ◽  
Pejman Rohani ◽  
Alun L. Lloyd ◽  
Matthew Keeling ◽  
Bryan T. Grenfell
Keyword(s):  
Waiting Time ◽  
Population Biology ◽  
Stochastic Dynamics ◽  
Theoretical Models ◽  
Human Populations ◽  
Community Size ◽  
Spatial Coupling ◽  
Statistical Measures ◽  
Population Sizes ◽  
The Impact

Measles epidemics in human populations exhibit what is perhaps the best empirically characterized, and certainly the most studied, stochastic persistence threshold in population biology. A critical community size (CCS) of around 250 000–500 000 separates populations where measles is predominantly persistent from smaller communities where there are frequent extinctions of measles between major epidemics. The fundamental mechanisms contributing to this pattern of persistence, which are long-lasting immunity to re-infection, recruitment of susceptibles, seasonality in transmission, age dependence of transmission and the spatial coupling between communities, have all been quantified and, to a greater or lesser level of success, captured by theoretical models. Despite these successes there has not been a consensus over whether simple models can successfully predict the value of the CCS, or indeed which mechanisms determine the persistence of measles over a broader range of population sizes. Specifically, the level of the CCS has been thought to be particularly sensitive to the detailed stochastic dynamics generated by the waiting time distribution (WTD) in the infectious and latent periods. We show that the relative patterns of persistence between models with different WTDs are highly sensitive to the criterion of comparison—in particular, the statistical measure of persistence that is employed. To this end, we introduce two new statistical measures of persitence—fade-outs post epidemic and fade-outs post invasion. Contrary to previous reports, we demonstrate that, no matter the choice of persistence measure, appropriately parametrized models of measles demonstrate similar predictions for the level of the CCS.

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