Variation In Population Dynamics Research Articles

Thermal tolerance in a south-east African population of the tsetse fly Glossina pallidipes (Diptera, Glossinidae): Implications for forecasting climate change impacts

For tsetse ( Glossina spp.), the vectors of human and animal trypanosomiases, the physiological mechanisms linking variation in population dynamics with changing weather conditions have not been well established. Here, we investigate high- and low-temperature tolerance in terms of activity limits and survival in a natural population of adult Glossina pallidipes from eastern Zambia. Due to increased interest in chilling flies for handling and aerial dispersal in sterile insect technique control and eradication programmes, we also provide further detailed investigation of low-temperature responses. In wild-caught G. pallidipes, the probability of survival for 50% of the population at low-temperatures was at 3.7, 8.9 and 9.6 °C (95% CIs: ±1.5 °C) for 1, 2 and 3 h treatments, respectively. At high temperatures, it was estimated that treatments at 37.9, 36.2 and 35.6 °C (95% CIs: ±0.5 °C) would yield 50% population survival for 1, 2 and 3 h, respectively. Significant effects of time and temperature were detected at both temperature extremes (GLZ, p<0.05 in all cases) although a time–temperature interaction was only detected at high temperatures ( p<0.0001). We synthesized data from four other Kenyan populations and found that upper critical thermal limits showed little variation among populations and laboratory treatments (range: 43.9–45.0 °C; 0.25 °C/min heating rate), although reduction to more ecologically relevant heating rates (0.06 °C/min) reduce these values significantly from ∼44.4 to 40.6 °C, thereby providing a causal explanation for why tsetse distribution may be high-temperature limited. By contrast, low-temperature limits showed substantial variation among populations and acclimation treatments (range: 4.5–13.8 °C; 0.25 °C/min), indicating high levels of inter-population variability. Ecologically relevant cooling rates (0.06 °C/min) suggest tsetses are likely to experience chill coma temperatures under natural conditions (∼20–21 °C). The results from acute hardening experiments in the Zambian population demonstrate limited ability to improve low-temperature tolerance over short (hourly) timescales after non-lethal pre-treatments. In flies which survived chilling, recovery times were non-linear with plateaus between 2–6 and 8–12 °C. Survival times ranged between 4 and 36 h and did not vary between flies which had undergone chill coma by comparison with flies which had not, even after factoring body condition into the analyses ( p>0.5 in all cases). However, flies with low chill coma values had the highest body water and fat content, indicating that when energy reserves are depleted, low-temperature tolerance may be compromised. Overall, these results suggest that physiological mechanisms may provide insight into tsetse population dynamics, hence distribution and abundance, and support a general prediction for reduced geographic distribution under future climate warming scenarios.

Modeling tradeoffs in avian life history traits and consequences for population growth

Variation in population dynamics is inherently related to life history characteristics of species, which vary markedly even within phylogenetic groups such as passerine birds. We computed the finite rate of population change ( λ) from a matrix projection model and from mark-recapture observations for 23 bird species breeding in northern Arizona. We used sensitivity analyses and a simulation model to separate contributions of different life history traits to population growth rate. In particular we focused on contrasting effects of components of reproduction (nest success, clutch size, number of clutches, and juvenile survival) versus adult survival on λ. We explored how changes in nest success or adult survival coupled to costs in other life history parameters affected λ over a life history gradient provided by our 23 Arizona species, as well as a broader sample of 121 North American passerine species. We further examined these effects for more than 200 passeriform and piciform populations breeding across North America. Model simulations indicate nest success and juvenile survival exert the largest effects on population growth in species with moderate to high reproductive output, whereas adult survival contributed more to population growth in long-lived species. Our simulations suggest that monitoring breeding success in populations across a broad geographic area provides an important index for identifying neotropical migratory populations at risk of serious population declines and a potential method for identifying large-scale mechanisms regulating population dynamics.

Stabilization of Population Fluctuations due to Cannibalism Promotes Resource Polymorphism in Fish

Resource polymorphism is a well-known phenomenon in many taxa, assumed to be a consequence of strong competition for resources and to be facilitated by stable environments and the presence of several profitable resources on which to specialize. In fish, resource polymorphism, in the form of planktivore-benthivore pairs, is found in a number of species. We gathered literature data on life-history characteristics and population dynamics for 15 fish species and investigated factors related to the presence of such resource polymorphism. This investigation indicated that early cannibalism and low overall population variability are typically associated with the presence of resource polymorphism. These findings match previously reported patterns of population dynamics for size-structured fish populations, whereby early cannibalism has been shown to decrease temporal variation in population dynamics and to equalize the profitability of the zooplankton and macroinvertebrate resources. Our study suggests that competition alone is not a sufficient condition for the development of resource polymorphism because overly strong competition is typically associated with increased temporal variation (environmental instability). We conclude that although resource competition is an important factor regulating the development of resource polymorphism, cannibalism may also play a fundamental role by dampening population oscillations and possibly by equalizing the profitability of different resources.

Explaining "Noise" as Environmental Variations in Population Dynamics

By integrating a population dynamic model with models of contaminant/stressor fate and transport and biological organism movement, researchers can capture the impact of spatial and temporal heterogeneity on population dynamics, and ultimately develop and implement improved management decisions and policies

Seasonal variations in population dynamics and biomass of two Unio pictorum mancus (Mollusca, Unionidae) populations from two lakes of different trophic state

Samples of Unio pictorum mancus collected monthly from spring 2003 to summer 2004 in the meso-oligotrophic Lake Maggiore and the eutrophic Lake Candia were compared to evaluate the influence of lake trophic conditions on mussel populations. Shell form, maximum age (8 years) and percentage of organic matter in the shell and soft tissues were similar in both lakes. However, comparisons between same size classes revealed that mussels from Lake Maggiore were generally older, their shells heavier and their soft tissues lighter than those from Lake Candia. Recruitment occurred in both populations in June-July. The frequency distributions of adult mussels (&gt;30 mm) and their soft tissues and shell biomasses in all size classes (range = 2 mm) were normal, but the curves of the mussels from Lake Candia were flat in comparison to those of mussels from Lake Maggiore. The median body size of Lake Maggiore mussels was 58 mm, while that of the Lake Candia population was 72 mm. During the study period the population density of each lake was fairly constant, whereas the population structure, and consequently the biomass, showed seasonal variations. The greatest differences were found between population density and shell and tissue biomass of the two populations, which were respectively 46.86 ind. m-2; 408 g d.w. m-2 and 38.67 g d.w. m-2 in Lake Maggiore, and 6.93 ind. m-2; 92.29 g d.w. m-2 and 14.04 g d.w. m-2 in Lake Candia. These values testify to the phenotypical plasticity of Unio pictorum mancus in relation to environmental characteristics, without excluding a possible genetic influence as a result of geographical isolation and the respective selection mechanisms. The influence exerted by the lake trophic level and by the physical environment on some population characteristics is discussed.

Linking growth strategies to long-term population dynamics in a guild of desert annuals

Summary 1 Combining long-term observational studies with comparative physiological ecology can yield a deeper understanding of the contribution of individual function to population and community dynamics. Sonoran Desert winter annuals exhibit striking year-to-year variation in population dynamics that is driven by variable precipitation, but species differ in the strength of demographic response to precipitation and hence in the degree of temporal variance in population dynamics. To understand the physiological mechanisms of differing population dynamic responses to environmental variation, we investigated interspecific differences in functional traits that mediate responsiveness to precipitation. 2 We conducted sequential harvests throughout the growing season to examine relative growth rate and biomass allocation patterns. We then related growth parameters to leaf-level carbon isotope discrimination (a time-integrated measure of water-use efficiency) and long-term demographic variation. 3 We hypothesized that water-use efficiency should trade-off with rapid growth rates. Furthermore, we hypothesized that species having efficient water use should have buffered population dynamics in dry years but sacrifice high growth and fecundity in wet years, resulting in low long-term variance in demographic success. Conversely, species with high growth capacity should be very responsive to infrequent periods of high precipitation and thus exhibit high temporal variance. 4 Species differed in seasonal relative growth rate and allocation patterns. Species with the highest relative growth rates rapidly deployed large leaf area displays following mid-season rainfall. Species with intermediate relative growth rates exhibited high biomass assimilation rates per unit leaf area. Species with low relative growth rates exhibited low leaf area ratios and low assimilation rates per unit leaf area. 5 Relative growth rate was positively related to leaf carbon isotope discrimination, consistent with a trade-off between growth rate and water-use efficiency. 6 Seasonal relative growth rate did not predict long-term demographic variance. However, leaf area plasticity in response to precipitation was positively related to long-term demographic variance. Our results illustrate how morphological and physiological traits influence demographic tracking of environmental variability and demonstrate how species differences in functional strategies determine population and community dynamics.

Stabilization of Population Fluctuations Due to Cannibalism Promotes Resource Polymorphism in Fish

Resource polymorphism is a well‐known phenomenon in many taxa, assumed to be a consequence of strong competition for resources and to be facilitated by stable environments and the presence of several profitable resources on which to specialize. In fish, resource polymorphism, in the form of planktivore‐benthivore pairs, is found in a number of species. We gathered literature data on life‐history characteristics and population dynamics for 15 fish species and investigated factors related to the presence of such resource polymorphism. This investigation indicated that early cannibalism and low overall population variability are typically associated with the presence of resource polymorphism. These findings match previously reported patterns of population dynamics for size‐structured fish populations, whereby early cannibalism has been shown to decrease temporal variation in population dynamics and to equalize the profitability of the zooplankton and macroinvertebrate resources. Our study suggests that competition alone is not a sufficient condition for the development of resource polymorphism because overly strong competition is typically associated with increased temporal variation (environmental instability). We conclude that although resource competition is an important factor regulating the development of resource polymorphism, cannibalism may also play a fundamental role by dampening population oscillations and possibly by equalizing the profitability of different resources.

DEMOGRAPHY OF CENTRAL AND MARGINAL POPULATIONS OF MONKEYFLOWERS (MIMULUS CARDINALISANDM. LEWISII)

Every species occupies a limited geographic area, but how spatiotemporal environmental variation affects individual and population fitness to create range limits is not well understood. Because range boundaries arise where, on average, populations are more likely to go extinct than to persist, range limits are an inherently population-level problem for which a demographic framework is useful. In this study, I compare demographic parameters and population dynamics between central and marginal populations of monkeyflowers, Mimulus cardinalis and M. lewisii, along an elevation gradient spanning both species' ranges. Central and marginal populations of both species differed in survival and fecundity. For M. lewisii, these components of fitness were higher in central than in marginal populations, but for M. cardinalis the converse was true. To assess spatiotemporal variation in population dynamics, I used transition matrix models to estimate asymptotic population growth rates (lambda) and found that population growth rates of M. lewisii were highest at the range center and reduced at the range margin. Population growth rates of M. cardinalis were highest at the range margin and greatly reduced at the range center. Life table response analysis decomposed spatiotemporal variation in lambda into contributions from each transition between life stages, finding that transitions from large nonreproductive and reproductive plants to the seed class and stasis in the reproductive class made the largest contributions to spatial differences in lambda. These transitions had only low to moderate sensitivities, indicating that differences in projected population growth rates resulted mainly from observed differences in transition matrix parameters and their underlying vital rates.

Spatial synchrony in population fluctuations: extending the Moran theorem to cope with spatially heterogeneous dynamics

The recent interest in the spatial structure and dynamics of populations motivated numerous theoretical and empirical studies of spatial synchrony, the tendency of populations to fluctuate in unison over regional areas. The first comprehensive framework applied to spatial synchrony was probably the one elaborated by P. A. P. Moran back in 1953. He suggested that if two populations have the same linear density‐dependent structure, the correlation between them will be equal to that between the local density‐independent conditions. Surprisingly, the consequences of violating the assumption that the dynamics of the populations are identical has received little attention. In this paper, making the assumption that population dynamics can be described by linear and stationary autoregressive processes, I show that the observed spatial synchrony between two populations can be decomposed into two multiplicative components: the demographic component depending on the values of the autoregressive coefficients, and the correlation of the environmental noise. The Moran theorem corresponds to the special case where the demographic component equals unity. Using published data, I show that the spatial variability in population dynamics may substantially contribute to the spatial variability of population synchrony, and thus should not be neglected in future studies.

Variation in population dynamics and movement patterns between two geographically isolated populations of the dusky hopping mouse (Notomys fuscus)

The ecology of the dusky hopping mouse (Notomys fuscus) was studied at Pelican Waterhole in south-west Queensland and Montecollina Bore in north-east South Australia over an eight-year period. Population parameters of N. fuscus differed markedly between the two study sites. Whilst the population at Montecollina Bore exhibited large fluctuations in size, captures at Pelican Waterhole were lower but more consistent. Recaptures between sessions at Montecollina Bore peaked at 60% but no individuals were recaptured at Pelican Waterhole. No evidence of seasonal breeding was recorded at either site. Male N. fuscus captured at Montecollina Bore were significantly heavier (average 31.4 g) than Pelican Waterhole animals (average 26.6 g). Over a 1–4-night period, the maximum linear distance moved by radio-collared individuals was 1.5 km (average 481 m) at Pelican Waterhole and 400 m (average 199 m) at Montecollina Bore. Differences in population dynamics between the two sites are ascribed to food availability and habitat quality. Whilst Pelican Waterhole may constitute a more stable, less degraded environment, Montecollina Bore appears to be defined by periods of either very high or very low resource availability depending on rainfall. The abundance of dingoes and low cat and fox activity may contribute to the persistence of N. fuscus at the two study sites.

Climate and spatio‐temporal variation in the population dynamics of a long distance migrant, the white stork

1. A central question in ecology is to separate the relative contribution of density dependence and stochastic influences to annual fluctuations in population size. Here we estimate the deterministic and stochastic components of the dynamics of different European populations of white stork Ciconia ciconia. We then examined whether annual changes in population size was related to the climate during the breeding period (the 'tap hypothesis' sensu Saether, Sutherland & Engen (2004, Advances in Ecological Research, 35, 185 209) or during the nonbreeding period, especially in the winter areas in Africa (the 'tube hypothesis'). 2. A general characteristic of the population dynamics of this long-distance migrant is small environmental stochasticity and strong density regulation around the carrying capacity with short return times to equilibrium. 3. Annual changes in the size of the eastern European populations were correlated by rainfall in the wintering areas in Africa as well as local weather in the breeding areas just before arrival and in the later part of the breeding season and regional climate variation (North Atlantic Oscillation). This indicates that weather influences the population fluctuations of white storks through losses of sexually mature individuals as well as through an effect on the number of individuals that manages to establish themselves in the breeding population. Thus, both the tap and tube hypothesis explains climate influences on white stork population dynamics. 4. The spatial scale of environmental noise after accounting for the local dynamics was 67 km, suggesting that the strong density dependence reduces the synchronizing effects of climate variation on the population dynamics of white stork. 5. Several climate variables reduced the synchrony of the residual variation in population size after accounting for density dependence and demographic stochasticity, indicating that these climate variables had a synchronizing effect on the population fluctuations. In contrast, other climatic variables acted as desynchronizing agents. 6. Our results illustrate that evaluating the effects of common environmental variables on the spatio-temporal variation in population dynamics require estimates and modelling of their influence on the local dynamics.

Spatial variation in population dynamics of juvenile Atlantic salmon: implications for conservation and management

Application of habitat models for predicting expected local densities of Atlantic Salmon Salmo salar in healthy populations has been hampered by a lack of generality in their fit to data from different systems. It is believed that this problem results at least in part from difficulties of effectively integrating factors that act across a range of spatial and temporal scales. Here, as an aid to developing more robust modelling and sampling methodologies, a simple process‐based model for local‐scale dynamics of Atlantic salmon juveniles is developed from first principles by integrating contemporary understanding of self‐thinning, density‐dependent growth and dispersal. The aim is to present a readily understood structure to illustrate the links between spawning and stocking strategies, habitat, migration and fish production. Based on this structure, contemporary understanding of the more complex biological processes that affect density, growth and habitat are discussed in relation to some of the key requirements of managers, including stocking for rehabilitation, assessment of predation impact and development of strategies for sampling populations effectively when deriving habitat‐production models. A major conclusion is that more structured, integrated research is required to provide the basic variables needed to model links between local and global scale habitat and fish production effectively. Nevertheless, application of the current understanding of the biology of Atlantic salmon should be of great benefit to managers in extracting key information from field surveys.

PROJECTION MATRIX ANALYSIS OF THE DEMOGRAPHY OF AN INVASIVE, NONNATIVE SHRUB (ARDISIA ELLIPTICA)

Despite recent advances in the study of invasive, nonnative species, we still understand very little about the variability of their population dynamics over space and time, and the processes that contribute to their demographic success. The goal of this study was to quantify the population dynamics of the invasive, subtropical shrub, Ardisia elliptica (Myrsinaceae), growing in a disturbed area of Everglades National Park, Florida, USA. We used bootstrap sampling and randomization tests to test hypotheses about spatial and tem- poral variation in population dynamics. Five populations spanning a range of habitats were studied for three years. Significant spatial and temporal variation in fruit production, relative growth, fates of vegetative individuals, and population growth rates were detected; however, spatial variation among populations had an overall stronger effect than temporal variation. Population growth rates were greater than 1 or not different from 1, implying that popu- lations are on average increasing in size. Similar to most other shrubs, prospective analysis showed that stasis of large stage classes had the highest elasticities. However, a retrospective analysis indicated that it was variation in growth to larger stage classes that contributed the most to observed variation in population growth rates. Simulations suggest that his- torically higher population growth rates of A. elliptica were necessary to produce current population sizes in Everglades National Park.

Seasonal Variations in Population Dynamics of Key Intertidal Molluscs at Two Contrasting Locations

The paper deals with the spatial and the temporal variability of the population dynamics of five key molluscan species at two rocky intertidal shores on the southern Saurashtra coastline of India. The intertidal belts of the two selected stations, Veraval and Diu, are about 100 km apart and differ in their coast characteristics and level of human interference. The slope and the substrate types of the two stations are not uniform and the exposure of intertidal belt of these predominantly rocky shores during low tides is also not significantly long. The study revealed that a general, species specific pattern of spatial and temporal variations existed in the population abundance and density of the species studied. There was considerable spatial variability in some species examined but most species showed no clear seasonal trends for the population abundance. The Veraval coast, in spite of being affected by heavy human interference, is still a favourable place for Chiton, Turbo cornatus and Turbo intercoastalis than Diu, though the latter is relatively less affected by anthropogenic influences. It appears that the subtratum type, short exposure duration and moderate wave action of the Arabian Sea are most active controlling factors for higher distribution of these species at Veraval.

Ramet demography of a nurse bromeliad in Brazilian restingas

Restingas are sandy coastal plains that stand between the sea and the Brazilian Atlantic forest mountains. The predominant restinga vegetation type in northern Rio de Janeiro, Brazil, is characterized by the formation of islands that begins with colonization by some pioneer herbs and/or woody plants. Pioneer plants are stress-resistant and nurse many other less-resistant plant species. Determining the spatiotemporal variation in the dynamics of nurse plants is essential to understand the ecological functioning of restingas as a whole. The goal of this study was to analyze the spatiotemporal variation in population dynamics of the nurse bromeliad Aechmea nudicaulis. We monitored A. nudicaulis ramets in different habitats, microhabitats, and years. We analyzed the spatiotemporal variation in demographic traits and in population growth rate. Results showed young ramet traits were more variable at the microhabitat level, and when variable, vegetative ramet traits varied at all spatiotemporal scales. Overall, λ values indicated that A. nudicaulis basically remained spatiotemporally stable as most of the λ values did not significantly differ from unity. Hence, the stability of A. nudicaulis in different microhabitats and habitats in the restinga may create several settlement opportunities for many other less-resistant species.

Spatial‐temporal population dynamics across species range: from centre to margin

Understanding the boundaries of species’ ranges and the variations in population dynamics from the centre to margin of a species’ range is critical. This study simulated spatial‐temporal patterns of birth and death rates and migration across a species’ range in different seasons. Our results demonstrated the importance of dispersal and migration in altering birth and death rates, balancing source and sink habitats, and governing expansion or contraction of species’ ranges in changing environments. We also showed that the multiple equilibria of metapopulations across a species’ range could be easily broken following climatic changes or physical disturbances either local or regional. Although we refer to our models as describing the population dynamics across whole species’ range, they should also apply to small‐scale habitats (metapopulations) in which species abundance follows a humped pattern or to any ecosystem or landscape where strong central‐marginal (C‐M) environmental gradients exist. Conservation of both central and marginal populations would therefore be equally important considerations in making management decisions.

Teleost Fish Genomes Contain a Diverse Array of L1 RetrotransposonLineages That Exhibit a Low Copy Number and High Rate of Turnover

Retrotransposable elements exhibit a wide range of variation in population dynamics, abundance, and lineage diversity among host genomes across taxa. This range of diversity is illustrated by a single well-defined constituent monophyletic clade of L1 non-LTR retrotransposons that is shared between mammalian and teleost fish genomes. Despite the clear phylogenetic relationships that exist between mammalian and teleost L1 sequences, these elements exhibit markedly different dynamics within their respective taxa. While mammalian genomes typically contain a single, abundant lineage of L1 elements that traces millions of years of evolution, the zebraflsh genome was recently shown to exhibit a high diversity of ancient lineages coexisting at a very low copy number and apparently exhibiting a high rate of turnover. In the present study, a combination of degenerate PCR, lineage-specific PCR, and genomic Southern blot analysis is utilized to demonstrate high L1 lineage diversity, low copy number, and a high proportion of polymorphic inserts in the genomes of the killifish species, Fundulus heteroclitus. Additional species surveyed by degenerate PCR include Cyprinodon variegatus, Rivulus marmoratus, and Menidia beryllina. These results further support the generality of the differences that exist in host-element dynamics between teleost fish and mammalian genomes with regard to L1 retrotransposons.

LONG-TERM DYNAMICS OF A GRASSLAND RODENT COMMUNITY

We examined long-term (1978–1999) population fluctuations and their influence on community structure in 6 species of rodents that are syntopic in old-field habitat in northeastern Kansas. Populations of all species fluctuated severalfold in abundance, with Sigmodon hispidus, Peromyscus maniculatus, and Reithrodontomys megalotis exhibiting annual cycles. Multiannual periodicities were evident for Microtus ochrogaster, P. maniculatus (3.5–4 years), and P. leucopus (7 years). Only Synaptomys cooperi lacked a discernable pattern in its abundance. Monthly abundances of 6 of 15 species-pairs positively covaried, suggesting similar responses to long-term environmental variation. In addition, several species-pairs showed time-lagged cross-correlations that indicate regular annual cycles, which were out of phase. Because of this variation in population dynamics within and among community members, the structure of this community varied considerably over time, indicating a nonequilibrial community. However, when looking at the community as a whole, 2 reoccurring long-term patterns in community structure emerge: an annual and a 3.5-year cycle. Annual cycles in community structure occurred because 3 of the 6 species showed annual cycles, whereas the 3.5-year cycle in community structure was probably due to the overwhelming influence of fluctuations in abundance of the numerically dominant prairie vole.

Long-Term Dynamics of a Grassland Rodent Community

We examined long-term (1978–1999) population fluctuations and their influence on community structure in 6 species of rodents that are syntopic in old-field habitat in northeastern Kansas. Populations of all species fluctuated severalfold in abundance, with Sigmodon hispidus, Peromyscus maniculatus, and Reithrodontomys megalotis exhibiting annual cycles. Multiannual periodicities were evident for Microtus ochrogaster, P. maniculatus, (3.5–4 years), and P. leucopus (7 years). Only Synaptomys cooperi lacked a discernable pattern in its abundance. Monthly abundances of 6 of 15 species-pairs positively covaried, suggesting similar responses to long-term environmental variation. In addition, several species-pairs showed time-lagged cross-correlations that indicate regular annual cycles, which were out of phase. Because of this variation in population dynamics within and among community members, the structure of this community varied considerably over time, indicating a nonequilibrial community. However, when looking at the community as a whole, 2 reoccurring long-term patterns in community structure emerge: an annual and a 3.5-year cycle. Annual cycles in community structure occurred because 3 of the 6 species showed annual cycles, whereas the 3.5-year cycle in community structure was probably due to the overwhelming influence of fluctuations in abundance of the numerically dominant prairie vole.

Seasonality, density dependence, and population cycles in Hokkaido voles.

Voles and lemmings show extensive variation in population dynamics regulated across and within species. In an attempt to develop and test generic hypotheses explaining these differences, we studied 84 populations of the gray-sided vole (Clethrionomys rufocanus) in Hokkaido, Japan. We show that these populations are limited by a combination of density-independent factors (such as climate) and density-dependent processes (such as specialist predators). We show that density-dependent regulation primarily occurs in winter months, so that populations experiencing longer winters tend to have a stronger delayed density-dependence and, as a result, exhibit regular density cycles. Altogether, we demonstrate that seasonality plays a key role in determining whether a vole population is cyclic or not.