Stability of pitcher-plant microfaunal populations depends on food web structure

Enrichment (increasing K) destabilizes simple consumer–resource interactions, but increasing food web complexity in various ways can remove this paradox of enrichment. We varied resources and number of omnivorous predators (mosquitoes) and tested for effects on the stability (persistence and temporal variability) of microfaunal populations living in pitcher plants. Top-down (omnivorous) effects were destabilizing, decreasing the persistence time of a rotifer, Habrotrocha rosa, and perhaps a microflagellate, Bodo sp. Enrichment effects were more complex, in part due to effects of shredding midges on resource availability, and in part due to interactions with predation. The persistence of Bodo increased with resource availability (more bacteria due to shredding by midges; no paradox of enrichment). Increasing resources by adding ants decreased persistence of H. rosa when mosquitoes were rare (paradox of enrichment), but the effect was reversed in leaves with significant colonization by mosquitoes. Thus, in the microfaunal community of pitcher plants, omnivorous predation tends to be destabilizing, and also tends to remove the paradox of enrichment.     

Spatial and temporal variation in mortality of newly settled damselfish: patterns,causes and co-variation with settlement

Local abundance and dynamics of sedentary species with a dispersing life stage reflect factors that influence input and loss rates to patches of suitable habitat. For reef fishes, more attention has focused on sources of variation in input (larval settlement) than on patterns and causes of subsequent losses. We estimated spatial and temporal variation in juvenile mortality of a tropical damselfish, yellow-tail dascyllus (Dascyllus flavicaudus; Pomacentridae), using a fixed density experiment that was repeated 5 times at the same eight mid-lagoon localities at Moorea, French Polynesia. There was little temporal variation in the overall percent of outplanted fish lost in 48 h among five time periods (range: 32-37%), whereas there was substantial variation among the sites in the average percent lost (range: 16-56%). Differences in loss rates among the sites were highly consistent among the time periods. Densities of predators of juvenile dascyllus varied substantially among the eight sites and were highly correlated with loss rate of dascyllus. We used the empirically derived relationship between predator density and damselfish loss rate to predict the loss rate of dascyllus at four additional sites, and there was excellent agreement between the predicted and observed loss rates. There was a strong positive relationship between predator densities at the 12 sites and structural attributes of the reefs that do not change on a fast time scale, suggesting why there was strong spatial and weak temporal variation in mortality rates, with no interaction between spatial and temporal variation. Natural settlement rates of yellow-tail dascyllus and of a close congener (humbug dascyllus, D. aruanus) varied among the sites, and settlement of the two species was inversely correlated (r=-0.68). Settlement of these species was not statistically correlated with variation in mortality rate, but there was a weak trend for settlement of yellow-tail dascyllus to be greater at sites with higher mortality (r=0.27), and for settlement of humbug dascyllus to be greater at sites with lower mortality (r=-0.32). We calculated that even these weak co-variances could reduce (yellow-tail dascyllus) or increase (humbug dascyllus) the spatial variance in density of 48-h-old recruits arising at settlement by 19 and 27% respectively. Taken together, the findings suggest that the interactions between and relative contributions of input and loss processes can differ substantially over a scale of a few kilometers, resulting in a mosaic of local patches characterized by different abundances and dynamics.     

Spatial dynamics of specialist seed predators on synchronized and intermittent seed production of host plants

Masting, the synchronized and intermittent seed production by plant populations, provides highly variable food resources for specialist seed predators. Such a reproductive mode helps minimize seed losses through predator satiation and extinction of seed predator populations. The seed predators can buffer the resource variation through dispersal or extended diapause. We developed a spatially explicit resource-consumer model to understand the effect of masting on specialist seed predators. The masting dynamics were assumed to follow a resource-based model for plant reproduction, and the population dynamics of the predator were represented by a spatially extended Nicholson-Bailey model. The resultant model demonstrated that when host plants reproduce intermittently, seed predator populations go locally extinct, but global persistence of the predator is facilitated by dispersal or extended diapause. Global extinction of the predator resulted when the intermittent reproduction is highly synchronized among plants. An approximate invasion criterion for the predators showed that negative lag-1 autocorrelation in seeding reduces invasibility, and positive lag-1 cross-correlation enhances invasibility. Spatial synchronization in seeding at local scale caused by pollen coupling (or climate forcing) further prevented invasion of the predators. If the predators employed extended diapause, extremely high temporal variability in reproduction was required for plants to evade the predators.     

Phenology of Predation on Insects in a Tropical Forest: Temporal Variation in Attack Rate on Dummy Caterpillars

In communities of tropical insects, adult abundance tends to fluctuate widely, perhaps in part owing to predator–prey dynamics. Yet, temporal patterns of attack rates in tropical forest habitats have not been studied systematically; the identity of predators of insects in tropical forests is poorly known; and their responses to temporal variation in prey abundance have rarely been explored. We recorded incidence and shape of marks of attacks on dummy caterpillars (proxy of predation rate) in a sub‐montane tropical forest in Uganda during a yearlong experiment, and explored correlations with inferred caterpillar abundance. Applying the highest and lowest observed daily attack rates on clay dummies over a realistic duration of the larval stage of butterflies, indicates that the temporal variation in attack rate could cause more than 10‐fold temporal variation in caterpillar survival. Inferred predators were almost exclusively invertebrates, and beak marks of birds were very scarce. Attack rates by wasps varied more over time than those of ants. Attack rates on dummies peaked during the two wet seasons, and appeared congruent with inferred peaks in caterpillar density. This suggests (1) a functional response (predators shifting to more abundant resource) or adaptive timed phenology (predators timing activity or breeding to coincide with seasonal peaks in prey abundance) of predators, rather than a numerical response (predator populations increasing following peaks in prey abundance); and (2) that predation would dampen abundance fluctuations of tropical Lepidoptera communities.     

Demographic response of plant populations to habitat fragmentation and temporal environmental variability

Many plant species currently exist in fragmented populations of different sizes, while they also experience unpredictable climatic fluctuation over time. However, we still understand little about how plant demography responds to such spatial and temporal environmental variability. We studied population dynamics of an understory perennial herb Trillium camschatcense in the Tokachi plain of Hokkaido, Japan, where a significant effect of forest fragmentation on seedling recruitment was previously reported. Four populations across a range of fragment sizes were studied for 6 years, and the data were analyzed using matrix population models. Per capita fecundity (the number of recruits per plant) varied greatly among populations, but the variation in population growth rates (λ) was mainly driven by the variation in stasis and growth rates, suggesting that the general trend of reduced fecundity in fragmented populations may not be readily translated into subsequent dynamics. Temporal variation in λ among years was more than 2 times larger than spatial variation among populations, and this result was likely attributable to the contrasting response of correlation structures among demographic rates. The among-population variation in λ was dampened by negative covariation between matrix elements possibly due to density-dependent regulation as well as an inherent constraint that some elements are not independent, whereas positive covariation between matrix elements resulted in large temporal variation in λ. Our results show that population dynamics responded differently to habitat fragmentation and temporal variability of the environment, emphasizing the need to discriminate these spatial and temporal variations in demographic models. Although no populations were projected to be declining in stochastic simulations, correlation between current habitat size and plant density implies historical λ is positively related to habitat size.     

Predator effects on herbivore and plant stability

Humans are rapidly altering the diversity and composition of ecological communities by accelerating rates of species extinctions and introductions. These changes in diversity are not random and disproportionately involve the addition or extinction of predators. Theoretical and microcosm studies suggest predator removal may either increase or decrease ecosystem stability. Here we test whether the addition or removal of predators affects aggregate biomass stability in 40 experiments carried out in six different ecosystems. Predators did not alter the temporal variability of autotroph biomass, but significantly destabilized herbivore biomass. The effects of predators on herbivore biomass stability varied significantly among ecosystems, with benthic and pelagic lake systems showing the greatest shifts. Consequently, the addition of predators to communities, as occurs in many conservation efforts, biological control programmes and species introductions, may lead to more variable system dynamics.     

Spatial dynamics of Microtus vole populations in continuous and fragmented agricultural landscapes

Small mammal populations often exhibit large-scale spatial synchrony, which is purportedly caused by stochastic weather-related environmental perturbations, predation or dispersal. To elucidate the relative synchronizing effects of environmental perturbations from those of dispersal movements of small mammalian prey or their predators, we investigated the spatial dynamics of Microtus vole populations in two differently structured landscapes which experience similar patterns of weather and climatic conditions. Vole and predator abundances were monitored for three years on 28 agricultural field sites arranged into two 120-km-long transect lines in western Finland. Sites on one transect were interconnected by continuous agricultural farmland (continuous landscape), while sites on the other were isolated from one another to a varying degree by mainly forests (fragmented landscape). Vole populations exhibited large-scale (>120 km) spatial synchrony in fluctuations, which did not differ in degree between the landscapes or decline with increasing distance between trapping sites. However, spatial variation in vole population growth rates was higher in the fragmented than in the continuous landscape. Although vole-eating predators were more numerous in the continuous agricultural landscape than in the fragmented, our results suggest that predators do not exert a great influence on the degree of spatial synchrony of vole population fluctuations, but they may contribute to bringing out-of-phase prey patches towards a regional density level. The spatial dynamics of vole populations were similar in both fragmented and continuous landscapes despite inter-landscape differences in both predator abundance and possibilities of vole dispersal. This implies that the primary source of synchronization lies in a common weather-related environment.     

Influences of the method of introduction of prey (Tetranychus urticae) and predators (Phytoseiulus persimilis) on the development of plant injury in tomato crops under glass

Two variants of the pest in first method of introduction of prey (Tetranychus urticae Koch) and predators (Phytoseiulus persimilis Athias-Henriot) on tomato crops were compared in a 80 m² glasshouse. As opposed to the second crop, the first crop was protected against spider mites by early and multiple releases of predators ensuring high spatial coincidence between prey and predators. Plant injury gradually increased in crop 1, whereas it first peaked and then decreased to low values in crop 2. Mean plant injury was higher in the former crop, and so was the degree of spatial variability. The lack of persistent control in crop 1 indicates that the predators suppressed, but did not annihilate the spider mites in the prey patches where the predators were introduced. This enabled the spider mites to resurge shortly after their enemies had disappeared due to lack of food. In crop 2, the way the biological control was conducted permitted the predators to achieve so high densities that they could annihilate the spider mites in most patches. Not only did this synchronize the prey populations but it also prevented the pest from a fast recovery. Moreover, predators did not disappear and maintained spider mite populations at low levels.     

Unexplained variability among spatial replicates in transient elasticity: implications for evolutionary ecology and management of invasive species

Understanding actual and potential selection on traits of invasive species requires an assessment of the sources of variation in demographic rates. While some of this variation is assignable to environmental, biotic or historical factors, unexplained demographic variation also may play an important role. Even when sites and populations are chosen as replicates, the residual variation in demographic rates can lead to unexplained divergence of asymptotic and transient population dynamics. This kind of divergence could be important for understanding long- and short- term differences among populations of invasive species, but little is known about it. We investigated the demography of a small invasive tree Psidium cattleianum Sabine in the rainforest of Hawaiʻi at four sites chosen for their ecological similarity. Specifically, we parameterized and analyzed integral projection models (IPM) to investigate projected variability among replicate populations in: (1) total population size and annual per capita population growth rate during the transient and asymptotic periods; (2) population structure initially and asymptotically; (3) three key parameters that characterize transient dynamics (the weighted distance of the structure at each time step from the asymptotic structure, the strength of the sub-dominant relative to the dominant dynamics, and inherent cyclicity in the subdominant); and (4) proportional sensitivity (elasticity) of population growth rates (both asymptotic and transient) to perturbations of various components of the life cycle. We found substantial variability among replicate populations in all these aspects of the dynamics. We discuss potential consequences of variability across ecologically similar sites for management and evolutionary ecology in the exotic range of invasive species.     

Relative growth rates of leaves from soybean grown under drought-stressed and irrigated field conditions

Abstract. The relative growth rates and leaf area were graphed against leaf area, normalized with respect to final leaf area, to assess the applicability of the Lockhart cell wall expansion equation to soybean, Glycine max (L.) Merr., leaf development under field conditions. For leaves that had completed more than 20% of their growth, relative growth rates decreased linearly with an increase in the normalized leaf area, indicating that these leaves were undergoing strictly expansive growth. Drought stress significantly decreased the relative growth rate of these larger leaves. Small leaves which had completed less than 20% of their growth, were found to have highly variable relative growth rates. The large variability in relative growth rates indicated that the Lockhart cell wall expansion equation was inadequate to evaluate the growth of these young leaves. Drought stress had virtually no influence on the relative growth rates observed in the small leaves.     

Contributions of mean temperature and temperature variation to population stability and community diversity

Future climate changes are predicted to not only increase global temperatures but also alter temporal variation in temperature. As thermal tolerances form an important component of a species’ niche, changes to the temperature regime have the capacity to negatively impact species, and therefore, the diversity of the communities they inhabit. In this study, we used protist microcosms to assess how mean temperature, as well as temporal variation in temperature, affected diversity. Communities consisted of seven species in a multitrophic food web. Each ecosystem was inoculated with the same abundances of each species at the start of the experiment, and species densities, Hill''s numbers (based on Shannon diversity), the number of extinctions, and the probability the microcosm contained predators were all calculated at the end of the experiment. To assess how mean temperature and temperature fluctuations affect stability, we also measured population densities through time. We found that increased temporal variation in temperature increased final densities, increased Hill''s numbers (at low mean temperatures), decreased rates of extinctions, and increased the probability that predators survived till the end of the experiment. Mean temperatures did not significantly affect either the number of extinctions or the probability of predators, but did reduce the positive effect of increased temporal variation in temperature on overall diversity. Our results indicate that climatic changes have the potential to impact the composition of ecological communities by altering multiple components of temperature regimes. However, given that some climate forecasts are predicting increased mean temperatures and reduced variability, our finding that increased mean temperature and reduced temporal variation are both generally associated with negative consequences is somewhat concerning.     

Linking frequencies of acorn masting in temperate forests to long-term population growth rates in a songbird: the veery (Catharus fuscescens)

Many terrestrial ecosystems are characterized by intermittent production of abundant resources for consumers, termed pulsed resources. The impact of resource pulses on populations downwind of the initial pulse are only beginning to be characterized, while the relationship between the frequencies of pulses and the long‐term growth rate of affected species is unknown. I monitored the reproductive success of veeries (Catharus fuscescens) breeding in oak‐dominated forest in southeastern New York State from 1998 to 2002. During this time veeries experienced high interannual variability in growth rates as a consequence of trophic cascades stemming from pulsed production of acorns. Rodent populations that benefited from acorns also depredated veery nests, while raptors that increased in response to rodent outbreaks are major predators on adult and juvenile birds. Veeries may recoup losses following low to moderate acorn crops that lead to rodent population declines. Thus, veeries fluctuate between years of positive and negative growth rate, however, long‐term population trends, and thus true source‐sink designation, cannot be made until the frequency of various year types is characterized. I simulated long‐term growth rates using reproductive parameters estimated from field studies and survivorship data from the literature. Simulations suggest that variability in the frequency of masting events in oaks can lead to ～10% fluctuation in long‐term growth rates in veeries. These studies suggest that temporal variability in masting dynamics has the potential to substantially influence songbird population trends. Furthermore, spatial variability in masting characteristics (e.g. the frequency of masting events and/or the size of seed crops) may greatly contribute to regional differences in songbird population trends. Because even less is known about the relationship between sizes of acorn crops and songbird populations, the influence of pulses in seed production on songbird population dynamics is likely to be underestimated.     

Optimal reproductive strategies in age-structured populations of zooplankton

SUMMARY. We describe a model of zooplankton population dynamics that accounts for differences in mortality and physiology among animals of different ages or sizes. The model follows changes in numbers of individuals and changes in individual and egg biomass through time and it expresses mortality and net assimilation as functions of animal size.
We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non-primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.
The model analysis shows how to assess age-dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality.     

Environmental colour affects aspects of single-species population dynamics

Single-species populations of ciliates (Colpidium and Paramecium) experienced constant temperature or white or reddened temperature fluctuations in aquatic microcosms in order to test three hypotheses about how environmental colour influences population dynamics. (i) Models predict that the colour of population dynamics is tinged by the colour of the environmental variability. However, environmental colour had no effect on the colour of population dynamics. All population dynamics in this experiment were reddened, regardless of environmental colour. (ii) Models predict that populations will track reddened environmental variability more closely than white environmental variability and that populations with a higher intrinsic growth rate (r) will track environmental variability more closely than populations with a low r. The experimental populations behaved as predicted. (iii) Models predict that population variability is determined by interaction between r and the environmental variability. The experimental populations behaved as predicted. These results show that (i) reddened population dynamics may need no special explanation, such as reddened environments, spatial subdivision or interspecific interactions, and (ii) and (iii) that population dynamics are sensitive to environmental colour, in agreement with population models. Correct specification of the colour of the environmental variability in models is required for accurate predictions. Further work is needed to study the effects of environmental colour on communities and ecosystems.     

Seasonal and habitat differences affect the impact of food and predation on herbivores: a comparison between gaps and understory of a tropical forest

Herbivore populations are influenced by a combination of food availability and predator pressure, the relative contribution of which is hypothesized to vary across a productivity gradient. In tropical forests, treefall gaps are pockets of high productivity in the otherwise less productive forest understory. Thus, we hypothesize that higher light availability in gaps will increase plant resources, thereby decreasing resource limitation of herbivores relative to the understory. As a result, predators should regulate herbivore populations in gaps, whereas food should limit herbivores in the understory. We quantified potential food availability and compared arthropod herbivore and predator densities in large forest light gaps and in the intact understory in Panama. Plants, young leaves, herbivores and predators were significantly more abundant per ground area in gaps than in the understory. This pattern was similar when we focused on seven gap specialist plant species and 15 shade-tolerant species growing in gaps and understory. Consistent with the hypothesis, herbivory rates were higher in gaps than the understory. Per capita predation rates on artificial caterpillars indicated higher predation pressure in gaps in both the dry and late wet seasons. These diverse lines of evidence all suggest that herbivores experience higher predator pressure in gaps and more food limitation in the understory.     

Small-scale spatial and temporal variation in the demographic processes underlying the large-scale decline of eiders in the Baltic Sea

The application of uniform conservation schemes often fails to account for small-scale spatial variation in the drivers of population decline. Demographic comparisons of imperilled populations across locations are therefore crucial for successful conservation, but progress is hampered by lack of long-term data from more than a single population. The recent large-scale decline of eider ducks (Somateria mollissima) in the Baltic Sea is ideal for determining to what extent mechanisms underlying population decline can be extrapolated over larger areas. We utilized stochastic demographic methods incorporating both environmental and sampling variation to assess small-scale spatial and temporal variation in the population dynamics of eiders at Söderskär (eastern range-margin) and Tvärminne (core breeding area), situated 130 km apart. The stochastic growth rate models accurately predicted the observed differences in the rate of decline between sites and time periods. At Söderskär, established breeder survival had by far the greatest elasticity, whereas elasticity was more evenly distributed among vital rates at Tvärminne. Although the study sites showed the single largest difference in fecundity, stochastic life table response experiment analyses revealed that reduced adult female survival at Tvärminne mainly determined the observed difference in growth rates between sites. In contrast, reduced fecundity primarily differentiated the past population increase from the present population decline at Söderskär. Our results demonstrate that different mechanisms may be associated with population decline across adjacent geographic locations, and indicate that dispersal of first-time breeders may be important for population dynamics. Safeguarding adult female survival and/or fecundity should be prioritized in management efforts.     

Concordant population dynamics of Lepidoptera herbivores in a forest ecosystem

It is frequently assumed that population fluctuations are largely independent within a community of trophically‐similar species, but this need not be so. If population fluctuations are partly synchronized or concordant, this will produce interannual variability in the community's aggregate abundance and generate temporal variance in ecosystem structure. We studied the community of Lepidoptera inhabiting northern hardwood forests in New Hampshire, USA, to evaluate the hypothesis that fluctuations in consumer communities can arise from concordant dynamics of constituent populations. Interannual comparisons of moth abundances for >75 species sampled at three sites over four years revealed that concordant dynamics contribute strongly to interannual variability in the abundance of consumers. A conspicuous decline in community abundance from 2004 to 2005 was the result of predominantly negative population growth rates of the component species, while an increase in community abundance from 2006 to 2007 was the result of predominantly positive population growth rates. Population dynamics most strongly linked species that feed in the early season (perhaps due to shared responses to climatic effects), but not species that might share natural enemies or host plants. The observed concordant dynamics introduced conspicuous temporal variation in the abundance of primary consumers relative to plants and secondary consumers, thereby altering the forest's trophic structure. Such variance in the aggregate abundance of forest primary consumers could generate time‐lagged fluctuations in abundances of secondary consumers and will generally have important consequences for ecosystem properties and processes that are nonlinear functions of consumer abundance, such as plant community structure and nutrient cycling.     

Population Dynamics and Life Tables of the Mango Mealybug, Rastrococcus invadens Williams, and its Introduced Natural Enemy Gyranusoidea tebygi Noyes in Benin

Life table data for Rastrococcus invadens and its introduced natural enemy Gyranusoidea tebygi were obtained in the field and in the laboratory. The mealybug population's potential rate of increase ranged from 0.066/day to 0.078/day. The potential for increase of the parasitoid was double that of its host. Seasonal fluctuations in abundance of R. invadens were followed from 1988 to 1992 on mango trees in southern Benin. The population density of R. invadens decreased during the rainy seasons and peaked during the dry seasons. Mealybug field sex ratios were extremely variable, and the impact of such variability on the mealybug's potential rate of increase was analyzed. The populations of the exotic encyrtid G. tebygi, introduced into Benin in 1988 for control of the pest, were synchronized with the host populations. The spatial patterns of parasitism distribution in relation to the host population density were either independent or directly density-dependent, both at the tree level and for larger zones. However, reducing the scale of analysis resulted in different types of relationships. The impact of predators was a minor factor in the population dynamics of the mealybug. Four of the six species of hyper-parasitoids attacking mealybugs parasitized by G. tebygi developed high populations. In the two orchards studied, mealybug populations eventually collapsed and disappeared. This fact is discussed as being an indication that the biological control of the mango mealybug by G. tebygi was achieved by non-equilibrium local dynamics, and should be evaluated in a meta-population perspective.     

Snowshoe hare demography during a cyclic population low

1. Snowshoe hare ( Lepus americanus Erxleben) populations were studied in south-west Yukon during the low phase of the 10-year population cycle. Food availability and predator abundance were manipulated in a factorial design to determine the importance of each factor in hare dynamics during this phase.
2. Food was abundant during the low phase, and snowshoe hares were not food limited.
3. Survival of hares was higher than at any other phase of the cycle, and predators were scarce, but >75% of hare deaths resulted from predation.
4. Food addition resulted in higher hare densities and better body condition than on control sites. There were no observable effects of food addition on population rate of increase, recruitment, survival or age structure.
5. Mammalian predator reduction resulted in higher hare densities, higher survival, better body condition and an older age structure. Relative to control populations, recruitment was lower and population rates of increase similar.
6. The joint manipulation of food addition + predator reduction had greater positive effects on hare density and body condition than either single factor manipulation. Survival was better than on control sites, and the age structure was older than on control sites. Population rates of increase were similar, but recruitment was higher on the control areas.
7. We conclude that snowshoe hare dynamics at the low of the cycle are dominated by the interaction of food and predation. Risk of predation also had indirect effects on snowshoe hare age structure and body condition.     

Belowground bud banks and meristem limitation in tallgrass prairieplant populations

Rhizome meristem populations were sampled in tallgrass prairie to quantify the size, grass?:?forb composition, and temporal and spatial variability of the soil bud bank and to compare fire effects on bud bank and seed bank composition. Soil cores (10.5 cm diameter, 15 cm deep) were collected from replicate annually and infrequently burned tallgrass prairie sites, and intact rhizomes and rhizome buds were censused. Bud bank densities ranged from approximately 600 to 1800 meristems/m(2) among sites and had high spatial and seasonal variability. In annually burned prairie, the total bud bank density was two-fold greater and the grass?:?forb meristem ratio was more than 30-fold greater than that of infrequently burned prairie. These patterns are opposite those observed in soil seed banks at this site. The rhizome population in annually burned prairie was 34% larger than the established aboveground tiller population. By contrast, the bud bank density in unburned prairie was significantly lower than aboveground stem densities, indicating possible belowground meristem limitation of stem density and net primary production on infrequently burned prairie. The patterns observed in this study suggest that the densities and dynamics of tallgrass prairie plant populations, as well as their response to disturbance (e.g., fire and grazing) and climatic variability, may be mediated principally through effects on the demography of belowground bud populations. Patterns of seed reproduction and seed bank populations have little influence on short-term aboveground population dynamics of tallgrass prairie perennials.