Intrinsic Biotic Factors Research Articles

The multicausal twilight of\xa0South American native mammalian predators (Metatheria, Sparassodonta)

Sparassodonts were the apex mammalian predators of South America throughout most of the Cenozoic, diversifying into a wide array of niches including fox-like and even saber-toothed forms. Their extinction is still controversial, with different authors suggesting competition with other predators (placental carnivorans, terror birds, and carnivorous opossums), extinction of prey, and climate change as causal explanations. Here, we analyse these hypotheses using a novel approach implicating Bayesian analyses. We find that speciation and extinction rates of sparassodonts can be correlated with (i) intrinsic biotic factors such as changes in body mass and diversity of sparassodonts, (ii) extrinsic biotic factors such as potential prey diversity, and iii) extrinsic abiotic factors like the atmospheric CO2, sea level, temperature, and uplift of the Andes. Thus, sparassodonts are a good example of a multilevel mixed model of evolution, where various factors drove the evolutionary history of this clade in a pluralistic way. There is no evidence for competition between Sparassodonta and others predators, and the effect of competition in the face of extinctions of fossil species should be tested and not assumed. Furthermore, we propose a novel approach for evaluating the fossil record when performing macroevolutionary analyses.

Intrinsic biotic factors and microsite conditions drive seedling survival in a species with masting reproduction.

Seedling recruitment following a masting event, where more fruits are produced in synchrony and intermittently compared with other species, plays a crucial role in determining species diversity and community structure. Such seedling recruitment can be superabundant, but followed by high mortality shortly thereafter. Differences in biotic factors such as seedling characteristics, competition, and herbivory, and microsite‐specific abiotic factors could determine seedling fate in space and time.In a subtropical forest in south China, for 2 years using censuses conducted every 1–2 months, we monitored 40 seed traps and 120, 1 m2 quadrats in five 1‐ha plots located from 1,400 to 1,850 m asl for the masting maple species, Acer campbellii subsp. sinense (Pax) P.C.DeJong. We measured biotic—conspecific and heterospecific seedling density, species richness, herbivory, seedling height, and leaf number—and abiotic—canopy openness, slope, and aspect—factors to assess drivers of seedling survival and evaluated A. campbellii subsp. sinense presence in the soil seed bank (SSB).The masting seed dispersal peak and seedling emergence peak occurred between October 2017 and January 2018, and May 2018, respectively. Of 688 selected seedlings, mortality was 92.7% within one year. No seeds were observed in the SSB. Seedling height and leaf number positively affected seedling survival, while seed placement as measured by aspect also showed effects on survival. Conspecific and heterospecific density and herbivory did not show any clear effect. Higher probabilities of seedling survival were found in areas with larger canopy openness (≥12% canopy gap size) and in steeper microsites (≥35°). Synthesis. Masting is mainly studied as a population‐level phenomenon from the fruiting tree perspective. Our study of individual seedling fate revealed that intrinsic biotic factors and seed placement were key drivers of survival. Although biotic determinants such as competition from conspecifics or heterospecifics or herbivory did not determine survival, their ubiquitous presence may be an underlying equalizer in community dynamics where seedlings that overcome biotic pressures, if placed at the right microsite, are at better odds at being recruited to the next life history stages.

Fitness Impact of Obligate Intranuclear Bacterial Symbionts Depends on Host Growth Phase.

According to text book definition, parasites reduce the fitness of their hosts whereas mutualists provide benefits. But biotic and abiotic factors influence symbiotic interactions, thus under certain circumstances parasites can provide benefits and mutualists can harm their host. Here we addressed the question which intrinsic biotic factors shape a symbiosis and are crucial for the outcome of the interaction between the obligate intranuclear bacterium Holospora caryophila (Alphaproteobacteria; Rickettsiales) and its unicellular eukaryotic host Paramecium biaurelia (Alveolata; Ciliophora). The virulence of H. caryophila, i.e., the negative fitness effect on host division and cell number, was determined by growth assays of several P. biaurelia strains. The performances of genetically identical lines either infected with H. caryophila or symbiont-free were compared. Following factors were considered as potentially influencing the outcome of the interaction: (1) host strain, (2) parasite strain, and (3) growth phases of the host. All three factors revealed a strong effect on the symbiosis. In presence of H. caryophila, the Paramecium density in the stationary growth phase decreased. Conversely, a positive effect of the bacteria during the exponential phase was observed for several host × parasite combinations resulting in an increased growth rate of infected P. biaurelia. Furthermore, the fitness impact of the tested endosymbionts on different P. biaurelia lines was not only dependent on one of the two involved strains but distinct for the specific combination. Depending on the current host growth phase, the presence of H. caryophila can be harmful or advantageous for P. biaurelia. Thus, under the tested experimental conditions, the symbionts can switch from the provision of benefits to the exploitation of host resources within the same host population and a time-span of less than 6 days.

Carbon dynamics of China’s forests during 1901–2010: The importance of forest age

The forest ecosystem plays a significant role in long-term carbon sequestration. The magnitude of a forest carbon sink is determined by the combination of intrinsic biotic factors (i.e. forest age) and extrinsic environmental driving factors (i.e. temperature, precipitation, nitrogen deposition). The mechanism of how forest age affects the carbon balance is still unclear. Furthermore, forest age is a useful surrogate variable for analyses of the impact of disturbances on forest carbon and an important parameter for assessing carbon mitigation potential of forests at regional scale. Without considering forest age, large uncertainties exist in the simulating forest carbon cycle at regional scale. In this study, we analyzed the effect of forest age information on carbon uptake of China’s forests based on a process-based model (Integrated Terrestrial Ecosystem Carbon budget, InTEC model) in the last century, with integration of two forest age maps at 1 km spatial resolution which were derived from inventory data and remote sensing AVHRR NDVI. Inter-annual variability of net primary productivity in China’s forests during 1901–2010 based on InTEC model coupled with inventory data and remote sensing data was similar with each other. Meanwhile, the comparison approach indicated that the errors of 5 years in forest age might cause uncertainties of 25% in simulated net ecosystem productivity of China’s forests. We also discussed the significance of forest age in ecosystem process-based model and the uncertainties of carbon balance of China’s forest ecosystem during 1901–2010. Besides, the hypothesis assumed that no large-scale deforestation occurred since1950s and mature forests (and older forests) were covered the whole China. We adjusted forest age structure for different forest types and regions to simulate the effect of changes in forest age on distribution of carbon balance in China. The important finding is that the loss of carbon sink in China’s forests induced by disturbances (i.e. deforestation, afforestation or natural disturbances) is about 3.80 Pg C during last century. Based this hypothesis, China’s forests in the last two decade manifested a large carbon sink (0.23 Pg C a - 1). Currently, many process-based models are not capable of reflecting the impact of land disturbances because the explicit forest age information are lacking. Our study incorporated the forest age in models successfully and explored the effect of forest age on the simulating carbon balance of forests. The application of forest age in large-scale carbon modeling can improve the accuracy of simulated carbon dynamics and explore the uncertainties in carbon cycle models.

Habitat breadth and geographic range predict diversity dynamics in marine Mesozoic bivalves

Numerous environmental and intrinsic biotic factors have been sought to explain patterns in diversity and turnover. Using taxonomically vetted and sampling-standardized data sets of more than 50,000 taxonomic occurrences in the Paleobiology Database (PaleoDB) we tested whether habitat breadth predicts genus durations and diversity dynamics of marine Mesozoic bivalves, and whether this effect is independent of the well-known positive relationship between geographic range and longevity. We defined the habitat breadth of a genus as a function of its realized ranges in water depth, substrate type, and grain size of the substrate. Our analysis showed that mean values of extinction and origination rates are significantly higher for narrowly adapted genera compared to broadly adapted genera, with differences being evident in all analyzed stratigraphic intervals. Linear models showed that both geographic range and habitat breadth have an independent effect on genus durations and on diversity dynamics. These results reaffirm the role of geographic range and furthermore suggest that habitat breadth is an equally important key predictor of extinction risk and origination probability in Mesozoic marine bivalves. Habitat generalists, regardless of their geographic range, are generally less prone to extinction. Conversely, widely distributed genera that are more specialized may be more endangered than one would expect from their geographic range alone. Extinction rates tend to be higher for specialized genera in both background and mass extinctions, suggesting that wide habitat breadth universally buffers against extinction. The trajectories of origination rates through time differ from those of extinction rates. Whereas there is no pronounced ecological selectivity in origination in the Triassic and most of the Jurassic, Cretaceous origination rates are higher for specialized genera. This may best be explained by diversity-dependence. When diversity levels reach a critical point a further increase in diversity is achieved by elevated origination rates of more specialized forms.

Succession in the aquatic Sarracenia purpurea community: deterministic or driven by contingency?

The development of a community through time, or succession, is generally described as the orderly replacement of species until a deterministic, stable endpoint is reached. However, stochastic factors, coupled with intrinsic biotic factors, such as herbivory or predation, can cause communities within the same habitat to become highly dissimilar in composition. Much research on the succession of terrestrial systems has been conducted, but factors influencing the succession of a terrestrial system may not apply to aquatic systems. To determine whether succession in an aquatic system is deterministic or dominated by contingency of stochastic factors, and the role that higher trophic level interactions and resources have in shaping successional patterns, I followed community development and dynamics of the intermediate and bottom trophic level (protozoans and bacteria) in the model Sarracenia purpurea pitcher plant system throughout an entire growing season. By comparing these dynamics across pitcher plant leaves within the same bog, I was able to determine whether there is a predictable pattern for community assembly in this aquatic community. The results from this study suggest that rather than a sequential replacement of early colonizers with more competitive species through time, competitively superior species establish in newly formed communities simultaneously with less competitive species, which coexist throughout the growing season. Community assembly in this system can also be altered by stochastic events. Resources and predators had a variable effect on the patterns of community change observed during succession. Patterns of community assembly were also dependent on the trophic level examined but, for the bottom trophic level, not on the sampling method used.

DNA damage in Gammarus fossarum sperm as a biomarker of genotoxic pressure: intrinsic variability and reference level

In the perspective of a biomonitoring application for assessing genotoxicity of freshwater ecosystems, the Comet assay has recently been developed on spermatozoa in the amphipod Gammarus fossarum, in order to propose a sensitive and reliable genotoxicity biomarker in an ecologically relevant freshwater species. The appropriate use of a genotoxicity biomarker requires good knowledge of its basal level and its natural variability related to intrinsic biotic and environmental abiotic factors. We propose a procedure for which the lowest biomarker variability related to methodological and intrinsic biotic factors is obtained and a reference value of biomarker basal response taking into account its spatio-temporal changes has been defined. A strong impact of spermatogenesis status and exposure time on the response to genotoxicant pressure was observed. These reports led us to select a standard organism, i.e., the mature male gammarid in precopula. No effect of temperature and conductivity on baseline DNA damage was observed in the laboratory for the tested range (6–24 °C and 300/600 μS cm −1). Similarly, no spatio-temporal change relative to season or the physico-chemical characteristics of the water was recorded during the field survey. On the basis of these results, a reference level with maximal threshold values has been proposed for the standard gammarid.

The influence of seasonality on biomarker responses in Mytilus edulis

The utility of some biomarkers in environmental monitoring may be limited due to the lack of knowledge that exists on how they respond to extrinsic abiotic and intrinsic biotic factors. During the present study we investigated the seasonal responses of three biomarkers, Neutral Red Retention, clearance/filtration rate and heart rate in the common blue mussel Mytilus edulis located in the Exe Estuary, UK during September 2006-September 2007. During the current study, a significant decrease in feeding rate was observed in mussels during June, July and August 2007, coinciding with the period following spawning when the mussels lay down nutrient reserves. Heart rate also increased between April and September 2007 and corresponded with times when mussels were spawning and laying down nutrient reserves. By integrating the individual biomarker responses into a Biomarker Response Index (BRI) we were able to identify times of the year when environmental impact was highest and hence when the timing of monitoring programmes using biomarkers should be carried out. For many years the lack of knowledge of normal physiological ranges of biomarkers has impeded their applied use, however by integrating biomarker responses into the BRI and creating an index of health, we have shown that we can limit the natural variability of individual responses; and thus we are better able to make informed judgements on the overall health status of these populations of mussels.

A scenario of human dispersal in the northwestern Mediterranean throughout the Early to Middle Pleistocene

Throughout the Early to Middle Pleistocene several origination and extinction bioevents led to a progressive rebuilding of the structure of the Mediterranean mammalian communities. Understanding whether faunal dispersal and turnovers developed on a backdrop of climatic changes or intrinsic biotic factors exerted a more important control, it is an outstanding interest in elucidating the ecological scenario, enabling humans to disperse towards and across the Mediterranean region. Although a link between human dispersal and climate change possibly exists, many archaeologists continue to reject environmental determinism. The first dispersal of some human groups towards the Mediterranean was undoubtedly part of the Early Pleistocene faunal renewal triggered by climate changes, but the increase of suitable prey and limited competition with other predators would have been beneficial to human peopling. To contribute to the debate, the Early to Middle Pleistocene fossil record of large Mediterranean mammals has been analysed with the aim of delineating the main biological events and processes which affected the evolution of faunal complexes, in turn enabling humans to disperse throughout the Mediterranean region. The results of this study confirm that the most important renewals of large Mediterranean mammalian fauna (due to both originations/dispersals and extinctions) are connected to major global climatic changes that, via migrations and dispersal events, altered palaeocommunity equilibrium, leading to new intra- and inter-guild dynamics. Changes in the richness and crop biomass of principal prey, as in the relative abundance of forest and open environment dwellers, possibly had an important role in opening favourable windows to human dispersal during the late Early Pleistocene. Nonetheless, a significant peopling occurred only after the faunal renewal of the Early to Middle Pleistocene transition and at the time of functional turnovers throughout the beginning of the Middle Pleistocene.

Scale dependent relationships between native plant diversity and the invasion of croftonweed (Eupatorium adenophorum) in southwest China

Croftonweed is an invasive plant in southwest China. We examined the relationships between its invasion patterns and native plant diversity at different spatio-temporal scales. At the 25 m2 scale, invasion success was negatively correlated with native plant diversity, indicating that resource availability might be the dominant factor regulating community invasibility. At the 400-m2 scale, both negative and positive relationships were detected, possibly identifying a spatial scale threshold where extrinsic environmental factors became more important to community invasibility. At the vegetation province scale, variations in physical environment outweighed the importance of intrinsic biotic factors and positive relationships between diversity and invader success were found. Native plant diversity also inhibited croftonweed over the course of community succession and at the early stages of invasion at local spatial scales. However, the changing relationship might be an artifact of sampling at different spatial scales.

Conservation of Red Colobus and Their Habitats

A review of the conservation status of red colobus indicates that ≥38.9% of the taxa are threatened with extinction in the near future. Although no taxon of red colobus appears to have gone extinct, many of their populations have. The major threats are hunting and habitat loss and degradation, but in some cases intrinsic biotic factors, such as predator-prey imbalance, are leading to serious declines in populations. I propose a general framework for evaluating conservation problems and possible solutions, with an emphasis on distinguishing between proximate and ultimate variables and the time scales involved. In general, most viable populations of red colobus occur in well-protected forests; usually national parks. I proffer recommendations to improve the conservation status of the parks, which will benefit red colobus and most other tropical forest species.

Lessons from the past: evolutionary impacts of mass extinctions.

Mass extinctions have played many evolutionary roles, involving differential survivorship or selectivity of taxa and traits, the disruption or preservation of evolutionary trends and ecosystem organization, and the promotion of taxonomic and morphological diversifications-often along unexpected trajectories-after the destruction or marginalization of once-dominant clades. The fossil record suggests that survivorship during mass extinctions is not strictly random, but it often fails to coincide with factors promoting survival during times of low extinction intensity. Although of very serious concern, present-day extinctions have not yet achieved the intensities seen in the Big Five mass extinctions of the geologic past, which each removed > or =50% of the subset of relatively abundant marine invertebrate genera. The best comparisons for predictive purposes therefore will involve factors such as differential extinction intensities among regions, clades, and functional groups, rules governing postextinction biotic interchanges and evolutionary dynamics, and analyses of the factors that cause taxa and evolutionary trends to continue unabated, to suffer setbacks but resume along the same trajectory, to survive only to fall into a marginal role or disappear ("dead clade walking"), or to undergo a burst of diversification. These issues need to be addressed in a spatially explicit framework, because the fossil record suggests regional differences in postextinction diversification dynamics and biotic interchanges. Postextinction diversifications lag far behind the initial taxonomic and morphological impoverishment and homogenization; they do not simply reoccupy vacated adaptive peaks, but explore opportunities as opened and constrained by intrinsic biotic factors and the ecological and evolutionary context of the radiation.

Evolutionary dynamics of Pragian Dacryoconarida (Lower Devonian, Tentaculitoidea): evidence from palaeontological data and °13C of marine carbonates from Czech Republic

Abstract A detailed palaeontological study was performed on 38 successive assemblages of dacryoconarids (Tentaculitoidea) sampled along the Cerna rokle section (Praha basin, Czech Republic). This section represents the whole Pragian stage (Lower Devonian) and roughly corresponds to a 6 Ma time span. Dacryoconarid assemblages change in abundance and diversity. Oxygen and carbon isotope compositions of the dacryoconarid-bearing carbonates were measured to evaluate the possible influence and control of the environmental conditions on the evolutionary dynamics of the dacryoconarid faunas. Large and rapid δ13C excursions occur in the marine carbonate sequence of the Cerna rokle section, some of which apparently correspond with faunal variations. However, no clear and simple relationship appears between carbon isotope ratio fluctuations and dacryoconarid evolutionary dynamics. Occurrence and extinction of the dacryoconarid species appear to be mainly related to biotic factors. Environmental variations cannot be regarded as having preponderantly influenced the dacryoconarid evolution, which more probably resulted from intrinsic biotic factors.

Ecological stasis and saltation: species richness change in planktic foraminifera during the late Paleocene to early Eocene, DSDP Site 577

Abstract A high resolution study of late Paleocene to early Eocene planktic foraminifera at DSDP Site 577 indicates the presence of three rapid faunal turnovers, or saltation events, with durations varying between 200–400 kyr and species turnover rates between 4–12 species/100 kyr. These saltation events are separated by slow faunal turnovers, or stasis intervals, with durations varying between 2.56–5.21 Myr and species turnover rates between 0.6–1.8 species/100 kyr. Each saltation event has different characteristics with disappearances equal to appearances in event T1, appearances dominate in event T2 that nearly double species richness, and primarily disappearances in event T3 that nearly halve species richness. Only event T2 near the P E boundary is associated with major and sudden environmental changes, as marked by a rapid warming in the deep ocean and high-latitude surface ocean and a negative excursion in carbonate δ13C values, that suggest a cause-effect relationship. The other two events occur during intervals of gradual environmental changes. We suggest that all three faunal events are triggered by the attainment of threshold conditions during the oceanic environmental changes. Threshold conditions may be attained through rapid environmental changes as in the case of event T2 near the P E boundary, or by gradual though cumulative environmental changes as appears to be the case in events T1 and T3. It is unclear, however, which environmental factors (e.g., temperature, salinity, nutrients, water-mass stratification) force rapid faunal turnovers or what role intrinsic biotic factors play.

Extinctions in the fossil record

Direct comparison of ancient extinctions to the present-day situation is difficult, because quantitative palaeontological data come primarily from marine invertebrates, fossilized species are usually drawn from the more abundant and widespread taxa, and time resolution is rarely better than 103— 104 years. A growing array of techniques permits quantitative error estimates on some of these potential biases, and allows calculation of species extinction intensities from genus-level data, which are more robust. Extensive as today’s species losses probably are, they have yet to equal any of the Big Five mass extinctions. Background extinction patterns are potential sources of insight regarding present-day biotic losses; over 90% of past species extinction has occurred at times other than the Big Five mass extinctions. Mean durations of fossil species vary by more than an order of magnitude even within clades, rendering uninformative any global average for background extinction. Taxon-specific variation is evidently related to intrinsic biotic factors such as geographic range and population size. Approaches to extinction analysis and prediction based on morphological variety or biodisparity should be explored as an adjunct or alternative to taxon inventories or phylogenetic metrics. Rebounds from mass extinctions are geologically rapid but ecologically slow; biodiversity communities typically requires 5-10 million years.