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171 results for “density-dependent”
Data from: Limited contributions of plant pathogens to density-dependent seedling mortality of mast fruiting Bornean trees
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Density-dependent patterns of multivariate selection on sperm motility and morphology in a broadcast spawning mussel
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Data from: Density-dependent effects on reproductive output in a capital breeding carnivore, the northern elephant seal (Mirounga angustirostris)
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Data from: Density-dependent space use affects interpretation of camera trap detection rates
<p>Camera-traps (CTs) are an increasingly popular tool for wildlife survey and monitoring. Estimating relative abundance in unmarked species is often done using detection rate as an index of relative abundance, which assumes a positive linear relationship with true abundance. This assumption may be violated if movement behavior varies with density, but the degree to which movement is density-dependent across taxa is unclear. The potential confounding of population-level relative abundance indices by movement depends on how regularly, and by what magnitude, movement rate and home-range size vary with density. We conducted a systematic review and meta-analysis to quantify relationships between movement rate, home range size, and density, across terrestrial mammalian taxa. We then simulated animal movements and CT sampling to test the effect of contrasting movement scenarios on CT detection rates. Overall, movement rate and home range size were negatively correlated with density and positively correlated with one another. The strength of the relationships varied significantly between taxa and populations. In simulations, detection rates were related to true abundance but underestimated change, particularly for slower moving species with small home ranges. In situations where animal space use changes markedly with density, we estimate that up to thirty percent of a true change in abundance may be missed due to the confounding effect of movement, making trend estimation more difficult. The common assumption that movement remains constant across densities is therefore violated across a wide range of mammal species. When studying unmarked species using CT detection rates, researchers and managers should consider that such indices of relative abundance reflect both density and movement. Practitioners interpreting changes in detection rates should be aware that observed differences may be biased low relative to true changes in abundance, and that further information on animal movement may be required to make robust inferences on population trends.</p>
Which enemies mediate distance- and density-dependent mortality of tree seeds and seedlings? A meta-analysis of fungicide, insecticide, and exclosure studies
<p>Conspecific negative distance- and density-dependence is believed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. SoilPlant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their relative importancegeneral effects at different plant life stages isare still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides, and exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that natural enemies cause stronger distance- and density-dependent mortality caused by natural enemies was most likely at the seedling stage than the seed stage. Fungicide treatments can change significantand was greater at higher mean annual temperatures. Seedling mortality was significantly weakened when fungi were removed. By contrast, negative distance- and density-dependent mortality to non-significance at the seedling stage. Negative conspecific distance- and density-dependence is not a general pattern at the seed stage. High seed mass reduced distance- and density-dependent mortality. Seed studies excluding only large mammals found significant negative conspecific distance-dependent mortality, but exclusion of all mammals resulted in a non-significant mortality.effect of conspecifics. Our study suggests that soilplant pathogens are a major cause of distance- and density-dependent mortality at the seedling stage, althoughwhile the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals respectively weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types, and assess how global change drivers may affect the dynamics of natural enemies and thus influence the strength of conspecific distance- and density-dependence.</p>
Density-dependent individual variation in male attractiveness in a wild field cricket
<p>Social environments modify a male's ability to attract females and thus affect its fitness. Theory implies that an individual's fitness should trade-off with its ability to cope with competition. Individuals are expected to solve this trade-off differently: some males should be more attractive at low but others instead at high density. This prediction has rarely been tested in the wild. We used an automated RFID-surveillance system to quantify for each hour of the day, over 30 days (i.e. almost the entire adult lifespan of our model organism), whether a male had attracted a female in its burrow. The data were collected across a range of naturally varying local densities in wild field crickets, <i>G.campestris</i>. We also estimated whether the shape of the relationship between attractiveness and density was under selection. At the population level, attractiveness increased from low to intermediate density, suggesting an Allee effect. Attractiveness subsequently declined at higher densities, for example, because of detrimental effects of increased competition. Opposite to expectations, males that were more attractive under low densities were also more attractive under higher densities. However, the increase in attractiveness with density varied among males, suggesting that Allee effects were individual-specific. Finally, selection was not acting on density-dependent attractiveness but males that lived longer acquired more mating partners. Our study reveals that social environments shape attractiveness in wild male insects, and imply the occurrence of individual-specific Allee effect that may be evolvable.</p>
Data from: Effective size in density-dependent two-sex populations: the effect of mating systems
Density dependence in vital rates is a key feature affecting temporal fluctuations of natural populations. This has important implications for the rate of random genetic drift. Mating systems also greatly affect effective population sizes, but knowledge of how mating system and density regulation interact to affect random genetic drift is poor. Using theoretical models and simulations, we compare Ne in short-lived, density dependent animal populations with different mating systems. We study the impact of a fluctuating, density dependent sex ratio and consider both a stable and a fluctuating environment. We find a negative relationship between annual Ne/N and adult population size N due to density dependence, suggesting that loss of genetic variation is reduced at small densities. The magnitude of this decrease was affected by mating system and life history. A male-biased, density dependent sex ratio reduces the rate of genetic drift compared to an equal, density independent sex ratio, but a stochastic change towards male-bias reduces the Ne/N ratio. Environmental stochasticity amplifies temporal fluctuations in population size, and is thus vital to consider in estimation of effective population sizes over longer time periods. Our results on the reduced loss of genetic variation at small densities, particularly in polygamous populations, indicate that density regulation may facilitate adaptive evolution at small population sizes.
Data from: Life-history evolution and density-dependent growth in experimental populations of yeast
We studied the evolution of the correlation between growth rate r and yield K in experimental lineages of the yeast Saccharomyces cerevisiae. First, we isolated a single clone every ~250 generations from each of eight populations selected in a glucose-limited medium for 5000 generations at ~6.6 population doublings per day (20 clones per line × 8 lines) and measured its growth rate and yield in a new, galactose-limited medium (with ~1.3 doubling per day). For most lines, r on galactose increased throughout the 5000 generations of selection on glucose while K on galactose declined. Next, we selected these 160 glucose-adapted clones in the galactose environment for ~120 generations and measured changes in r and K in galactose. In general, growth rate increased and yield declined, and clones that initially grew slowly on galactose improved more than did faster clones. We found a negative correlation between r and K among clones both within each line and across all clones. We provide evidence that this relationship is not heritable and is a negative environmental correlation rather than a genetic trade-off.
Data from: Sex-specific density-dependent secretion of glucocorticoids in lizards: insights from laboratory and field experiments
Negative density feedbacks have been extensively described in animal species and involve both consumptive (i.e. trophic interactions) and non-consumptive (i.e. social interactions) mechanisms. Glucocorticoids are a major component of the physiological stress response and homeostasis, and therefore make a good candidate for proximate determinants of negative density feedbacks. Here, we combined laboratory and field experiments with enclosed populations to investigate the relationship between density, social stress and plasma corticosterone levels in the common lizard Zootoca vivipara. This species exhibits strong negative density feedbacks that affect females more than males, and its life history is sensitive to experimentally-induced chronic elevation of corticosterone plasma levels. We found that prolonged crowding in the laboratory can trigger a chronic secretion of corticosterone independent from food restriction. In the field experiments, corticosterone levels of females were not affected by population density. Corticosterone levels of males increased with population density but only during the late activity season in a first field experiment where we manipulated density. They also increased with density during the mating season but only in populations with a female-biased sex ratio in a second field experiment where we crossed manipulated density and adult sex ratio. Altogether, our results provide limited evidence for a role of basal corticosterone secretion in density feedbacks in this species. Context and density-dependent effects in males may arise from changes in behavior caused by competition for resources, male–male competition, and mating.
Data from: Density-dependent energy use contributes to the self-thinning relationship of cohorts
In resource-limited populations, an increase in average body size can occur only with a decline in abundance. This is known as self-thinning, and the decline in abundance in food-limited populations is considered proportional to the scaling of metabolism with body mass. This popular hypothesis may be inaccurate, because self-thinning populations can also experience density-dependent competition, which could alter their energy use beyond the predictions of metabolic scaling. This study tested whether density-dependent competition has an energetic role in self-thinning, by manipulating the abundance of the fish Macquaria novemaculeata and tank size to partition the effects of competition from metabolic scaling. We found that self-thinning can be density dependent and that changes in intraspecific competition may be more influential than metabolic scaling on self-thinning relationships. The energetic mechanism we propose is that density-dependent competition causes variation in the allocation of energy to growth, which alters the energetic efficiency of self-thinning cohorts. The implication is that food-limited cohorts and populations with competitive strategies that encourage fast-growing individuals will have less body mass at equilibrium and higher mortality rates. This finding sheds light on the processes structuring populations and can be used to explain inconsistencies in the mass-abundance scaling of assemblages and communities (the energetic-equivalence rule).
Data from: Female density-dependent chemical warfare underlies fitness effects of group sex ratio in flour beetles
In animals, skewed sex ratios can affect individual fitness either via sexual (e.g. intersexual conflict or intrasexual mate competition) or non-sexual interactions (e.g. sex-specific resource competition). Because most analyses of sex ratio focus on sexual interactions, the relative importance of sexual vs. non-sexual mechanisms remains unclear. We tested both mechanisms in the flour beetle Tribolium castaneum, where male-biased sex ratios increase female fitness relative to unbiased or female-biased groups. Although flour beetles show both sexual and non-sexual (resource) competition, we found that sexual interactions did not explain female fitness. Instead, female fecundity was dramatically reduced even after a brief exposure to flour conditioned by other females. Earlier studies suggested that secreted toxins might mediate density-dependent population growth in flour beetles. We identified ethyl- and methyl- benzoquinone (EBQ and MBQ; "quinones"), as components of adult stink glands that regulate female fecundity. In female-biased groups (i.e. at high female density), females upregulated quinones and suppressed each other's reproduction. In male-biased groups, low female density and associated low quinone levels maximized fecundity. Thus, females appear to use quinones as weapons for female-specific, density-dependent interference competition. Our results underscore the importance of non-sexual interference competition that may often underlie the fitness consequences of skewed sex ratios.
Data from: Cyclic population dynamics and density-dependent intransitivity as pathways to coexistence between co-occurring annual plants
1. Recent studies have brought renewed attention to the importance of complex species interactions - notably intransitive interactions - to patterns of plant community diversity. One underappreciated avenue through which intransitivity can occur is through cyclic population dynamics. Though such cyclic intransitive relationships have been extensively studied in predator-prey systems, evidence of their importance in competitive communities, notably plant communities, is more limited. Most studies of coexistence in plant communities assume fixed-point coexistence even while utilizing models that allow for cyclic population dynamics. 2. In this paper, we explore the potential for density-dependent, cyclic population dynamics and intransitivity in a model for annual plants. We then examine how these density-dependent cycles impact mutual invasibility and ultimately stable coexistence between plant species pairs. We do this using data collected from four co-occurring annual plant species living in natural wildflower communities in SW Western Australia. To maximize the number of biologically plausible pathways by which coexistence mediated by density-dependent cyclic intransitivity can occur, we use an annual plant model that allows for competitive direct interactions, facilitative direct interactions, and higher-order interactions between species. 3. Results from our empirically-parameterized model suggest that monocultures of all four focal species can have cyclic solutions with periodicity greater than 1 under sunny ("open") or shaded field conditions. Cyclic patterns drive variation in annual abundance patterns, with stable solutions for persistent monocultures and invasibility potential (the capacity of one population to invade another) common. Mutual invasibility in the face of cyclic population dynamics was found for just one of six species pairs, only under open environmental conditions. Our results illustrate the potential for cyclic intransitivity to both drive and prevent stable coexistence in environmentally heterogeneous biological communities. 4. Synthesis. We provide analytical and empirical evidence that coexistence in competitive communities (annual plants) can be achieved under non-equilibrium circumstances, through density-dependent cyclic intransitivity. Our results suggest that cyclic population dynamics may be common and important for coexistence dynamics in some types of communities. In such communities, the exploration of stable coexistence should therefore include consideration of cyclic as well as fixed-point equilibria for maximal accuracy.
Data from: Transgenerational effects modulate density-dependent prophylactic resistance to viral infection in a lepidopteran pest
There is an increasing appreciation of the importance of transgenerational effects on offspring fitness, including in relation to immune function and disease resistance. Here, we assess the impact of parental rearing density on offspring resistance to viral challenge in an insect species expressing density-dependent prophylaxis (DDP); i.e. the adaptive increase in resistance or tolerance to pathogen infection in response to crowding. We quantified survival rates in larvae of the cotton leafworm (Spodoptera littoralis) from either gregarious- or solitary-reared parents following challenge with the baculovirus S. littoralis nucleopolyhedrovirus. Larvae from both the parental and offspring generations exhibited DDP, with gregarious-reared larvae having higher survival rates post-challenge than solitary-reared larvae. Within each of these categories, however, survival following infection was lower in those larvae from gregarious-reared parents than those from solitary-reared, consistent with a transgenerational cost of DDP immune upregulation. This observation demonstrates that crowding influences lepidopteran disease resistance over multiple generations, with potential implications for the dynamics of host–pathogen interactions.
Data from: Evolution of density-dependent movement during experimental range expansions
Range expansions and biological invasions are prime examples of transient processes that are likely impacted by rapid evolutionary changes. As a spatial process, range expansions are driven by dispersal and movement behaviour. While it is widely accepted that dispersal and movement may be context-dependent, for instance density-dependent, and best represented by reaction norms, the evolution of density-dependent movement during range expansions has received little experimental attention. We therefore tested current theory predicting the evolution of increased movement at low densities at range margins using highly replicated and controlled range expansion experiments across multiple genotypes of the protist model system Tetrahymena thermophila. Although rare, we found evolutionary changes during range expansions even in the absence of initial standing genetic variation. Range expansions led to the evolution of negatively density-dependent movement at range margins. In addition, we report the evolution of increased intra-strain competitive ability and concurrently decreased population growth rates in range cores. Our findings highlight the importance of understanding movement and dispersal as evolving reaction norms and plastic life-history traits of central relevance for range expansions, biological invasions and the dynamics of spatially structured systems in general.
Data from: Facilitation among plants can accelerate density-dependent mortality and steepen self-thinning lines in stressful environments
The speed and slope of plant self-thinning are all affected by plant-plant interactions across environmental gradients. Possible mechanisms driving the self-thinning dynamics include the relative strength of root vs. shoot competition, and the interplay between competition and facilitation. Although these mechanisms often act in concert, their relative importance has not yet been fully explored. We used both a one-layer and a two-layer zone-of-influence (ZOI) model to examine how competition and facilitation drive self-thinning across stress gradients. As a development of the traditional ZOI model, the two-layer version explicitly models shoot and root growth and neighbor interactions, and thus the overall size-symmetry of competition is regulated by the relative strength of root vs. shoot competition. One-layer model simulations revealed that increasingly asymmetric competition accelerated thinning, and steepened (slope ranged from about -1 to -4/3) and lowered self-thinning lines. Stress slowed down density-dependent mortality considerably when competition was not completely symmetric. Stress significantly decreased the self-thinning intercept, while facilitation simply counteracted stress effects. Both stress and facilitation showed little effect on the slope. In the two-layer model, both stress and facilitation affected mortality in the same way as in the one-layer version when competition was not completely symmetric. Different from the one-layer model, the two-layer version showed that the effects of stress and facilitation on the self-thinning slope were mediated by the asymmetry of competition. As stress increased, the overall asymmetry of competition shifted from asymmetric to symmetric due to increased relative strength of root competition. High stress thus dramatically flattened self-thinning lines, whereas the inclusion of facilitation counteracted stress and led to steeper self-thinning lines. Our two-layer model is based on the current knowledge of plant-plant interactions, and better represents ecological realities. It can help elaborate experiments for testing the role of competition and facilitation in driving plant population dynamics.
Data from: Density-dependent vulnerability of forest ecosystems to drought
Climate models predict increasing drought intensity and frequency for many regions, which may have negative consequences for tree recruitment, growth, and mortality, as well as forest ecosystem services. Furthermore, practical strategies for minimizing vulnerability to drought are limited. Tree population density, a metric of tree abundance in a given area, is a primary driver of competitive intensity among trees, which influences tree growth and mortality. Manipulating tree population density may be a mechanism for moderating drought-induced stress and growth reductions, although the relationship between tree population density and tree drought vulnerability remains poorly quantified, especially across climatic gradients. In this study, we examined three long-term forest ecosystem experiments in two widely-distributed North American pine species, ponderosa pine Pinus ponderosa (Lawson & C. Lawson) and red pine Pinus resinosa (Aiton), to better elucidate the relationship between tree population density, growth, and drought. These experiments span a broad latitude and aridity range and include tree population density treatments that have been purposefully maintained for several decades. We investigated how tree population density influenced resistance (growth during drought) and resilience (growth after drought compared to pre-drought growth) of stand-level growth during and after documented drought events. Our results show that relative tree population density was negatively related to drought resistance and resilience, indicating that trees growing at lower densities were less vulnerable to drought. This result was apparent in all three forest ecosystems, and was consistent across species, stand age, and drought intensity. Synthesis and applications. Our results highlighted that managing pine forest ecosystems at low tree population density represents a promising adaptive strategy for reducing the adverse impacts of drought on forest growth in coming decades. Nonetheless, the broader applicability of our findings to other types of forest ecosystems merits additional investigation.
Figure 2 in Host instars preference, density-dependent parasitism and behavioral perspective of parasitoids (Aphidius colemani, Aphidius matricariae and Aphelinus abdominalis) in Aphis glycines and Aphis gossypii
Figure 2: Parasitism percentage of parasitoids (Ad. colemani, Ad. matricariae and Al. abdominalis) on different host instars of (A) As. glycines (n= 30) and (B) As. gossypii (n= 30).
Figure 4 in Host instars preference, density-dependent parasitism and behavioral perspective of parasitoids (Aphidius colemani, Aphidius matricariae and Aphelinus abdominalis) in Aphis glycines and Aphis gossypii
Figure 4: Parasitism percentage of parasitoids (Ad. colemani, Ad. matricariae and Al. abdominalis) at different host density levels of (A) As. glycines and (B) As. gossypii. C1 (1:1) Control, C2 (10:1), C3 (50:5), C4 (100:10), C5 (200:20).
Figure 3 in Host instars preference, density-dependent parasitism and behavioral perspective of parasitoids (Aphidius colemani, Aphidius matricariae and Aphelinus abdominalis) in Aphis glycines and Aphis gossypii
Figure 3: Comparison of parasitism of parasitoids (Ad. colemani, Ad. matricariae and Al. abdominalis) on different host density levels of (A) As. glycines and (B) As. gossypii. C1 (1:1) Control, C2 (10:1), C3 (50:5), C4 (100:10), C5 (200:20).
Data from: Density-dependent, central-place foraging in a grazing herbivore: competition and trade-offs in time allocation near water
Optimal foraging theory addresses one of the core challenges of ecology: predicting the distribution and abundance of species. Tests of hypotheses of optimal foraging, however, often focus on a single conceptual model rather than drawing upon the collective body of theory, precluding generalization. Here we demonstrate links between two established theoretical frameworks predicting animal movements and resource use: central-place foraging and density-dependent habitat selection. Our goal is to better understand how the nature of critical, centrally placed resources like water (or minerals, breathing holes, breeding sites, etc.) might govern selection for food (energy) resources obtained elsewhere – a common situation for animals living in natural conditions. We empirically test our predictions using movement data from a large herbivore distributed along a gradient of water availability (feral horses, Sable Island, Canada, 2008–2013). Horses occupying western Sable Island obtain freshwater at ponds while in the east horses must drink at self-excavated wells (holes). We studied the implications of differential access to water (time needed for a horse to obtain water) on selection for vegetation associations. Consistent with predictions of density-dependent habitat selection, horses were reduced to using poorer-quality habitat (heathland) more than expected close to water (where densities were relatively high), but were free to select for higher-quality grasslands farther from water. Importantly, central-place foraging was clearly influenced by the type of water-source used (ponds vs. holes, the latter with greater time constraints on access). Horses with more freedom to travel (those using ponds) selected for grasslands at greater distances and continued to select grasslands at higher densities, whereas horses using water holes showed very strong density-dependence in how habitat could be selected. Knowledge of more than one theoretical framework may be required to explain observed variation in foraging behavior of animals where multiple constraints simultaneously influence resource selection.
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Allen Brain Atlas
Allen Brain Atlas is an Allen Institute collection of brain map atlases, datasets, APIs, and analysis tools covering mouse, human, and non-human primate brain resources.
Annotated Behaviour and Observability Dataset (ABODe)
ABODe is a University of Edinburgh DataShare dataset for behavior classification in group-housed mice using home-cage video, identities, bounding boxes, ground-plate positions, and annotator labels.
DANDI Archive for NWB datasets
DANDI is a BRAIN Initiative archive for publishing and sharing neurophysiology data, including electrophysiology, optophysiology, and behavioral data packaged as NWB and related standards.
International Brain Laboratory public data
The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.