Temporal Variation In Populations Research Articles

Conservation and production responses vary by disturbance intensity in a long-term forest management experiment.

Reductions in management intensity are often proposed to support a broader range of beneficial ecosystem responses than traditional management approaches. However, few studies evaluate ecosystem responses across approaches. Also, managers lack information about how species traits mediate responses across management approaches, a potentially substantial source of spatial and temporal variation in population and community responses that if ignored may hinder effectiveness of management programs. We used data collected over eight years from a manipulative experiment to test how four forest management strategies influenced avian community composition and wood production. After harvesting, we evaluated responses to three levels of plant cover suppression (Light, Moderate, and Intensive herbicide applications) in relation to a control without herbicide. We predicted the Moderate and Intensive treatments would exert strong negative effects on leaf-gleaning insectivores, including species of conservation concern due to long-term population declines. However, given high forest productivity, we expected temporal duration of effects to be short. Richness of leaf-gleaning bird species was reduced by 20-50% during the first four years post-harvest (when herbicide treatments were on-going), but the effect size declined over the next four years once treatments were completed (13-20% reduction). Effect sizes were substantially smaller for the non-leaf-gleaner group during years 1-4 (19-27%) and disappeared during years 5-8 (2-3%). However, in our final year of observation, we did find an average of five fewer non-leaf-gleaner species on Light vs. Control units. In the last two years of observation, turnover probabilities for the leaf-gleaner species remained higher on all treatments compared to the Control (0.11-0.21), indicating that new species continued to colonize treatments. Planted conifers were 40-44% taller and 74-81% larger in diameter in the Moderate and Intensive treatments compared to the Control, leading to substantial gains in wood biomass. Current practices provided more balance between two ecosystem responses, avian diversity and wood production, compared to less intensive alternatives. When short-term negative effects occur, the spatial distribution of harvesting and regeneration regionally indicates that habitat is often available locally to support leaf-gleaning and non-leaf-gleaning bird populations while releasing other portions of the region for high priority conservation objectives including late-successional forest reserves.

Experimental evidence indicates variable responses to forest disturbance and thermal refugia by two plethodontid salamanders

Understanding how natural and anthropogenic disturbances affect sensitive species is critical to support conservation programs as land use activities and climatic conditions change. Forest management provides a range of ecosystem services to expanding human populations including production of substantial amounts of woody biomass, thereby reducing area under management and increasing opportunity for conservation designations. However, relatively little experimental information is available to describe how manipulating habitat at multiple scales may affect spatial and temporal variation in populations of climate-sensitive forest taxa. We conducted a Before-After Control-Impact experiment over seven years to evaluate responses of two species of Plethodontid salamanders in operational treatment (harvest, replanting, and herbicide application) and control units, Oregon, USA. In addition, we capitalized on existing variation in downed wood size and accounted for potential behavioral responses to evaluate the thermal refugia hypothesis. For Oregon slender salamanders (Batrachoseps wrighti), mean plot-level occupancy (90% CRI) was increased an estimated 11% (1.11; 0.62–2.1) and estimated mean abundance reduced 16% (0.84; 0.54–1.4) post-harvest. For Ensatina (Ensatina eschscholtzii), mean occupancy was reduced an estimated 80% (0.20; 0.08–0.47) and estimated mean abundance reduced 63% (0.37; 0.22–0.65) post-harvest. We found strong evidence of positive associations for both species with downed wood amount. As predicted, we found ambient temperatures to be higher in harvest than control units. Also, internal downed wood temperatures were warmer in harvested units, suggesting these structures may not have provided adequate thermal refugia. Application of an experimental framework provided evidence about both stand and structure level responses to active management. Habitat structures did not appear to buffer against substantial variation in local climate but evidence was equivocal about importance of these structures to population retention. Monitoring of recruitment and retention of downed wood through subsequent rotations can provide critical information to reduce trade-offs between wood production and conservation of climate sensitive taxa.

Seasonal and temporal variation in population of mustard sawfly, Athalia lugens proxima on different species of rapeseed-mustard in relation to weather parameters

Seasonal and temporal variation in population of mustard sawfly, <i>Athalia lugens proxima</i> on different species of rapeseed-mustard in relation to weather parameters

Seasonal Variation in Population Abundance and Chytrid Infection in Stream-Dwelling Frogs of the Brazilian Atlantic Forest.

Enigmatic amphibian declines were first reported in southern and southeastern Brazil in the late 1980s and included several species of stream-dwelling anurans (families Hylodidae and Cycloramphidae). At that time, we were unaware of the amphibian-killing fungus Batrachochytrium dendrobatidis (Bd); therefore, pollution, habitat loss, fragmentation and unusual climatic events were hypothesized as primary causes of these declines. We now know that multiple lineages of Bd have infected amphibians of the Brazilian Atlantic forest for over a century, yet declines have not been associated specifically with Bd outbreaks. Because stream-dwelling anurans occupy an environmental hotspot ideal for disease transmission, we investigated temporal variation in population and infection dynamics of three stream-adapted species (Hylodes asper, H. phyllodes, and Cycloramphus boraceiensis) on the northern coast of São Paulo state, Brazil. We surveyed standardized transects along streams for four years, and show that fluctuations in the number of frogs correlate with specific climatic variables that also increase the likelihood of Bd infections. In addition, we found that Bd infection probability in C. boraceiensis, a nocturnal species, was significantly higher than in Hylodes spp., which are diurnal, suggesting that the nocturnal activity may either facilitate Bd zoospore transmission or increase susceptibility of hosts. Our findings indicate that, despite long-term persistence of Bd in Brazil, some hosts persist with seasonally variable infections, and thus future persistence in the face of climate change will depend on the relative effect of those changes on frog recruitment and pathogen proliferation.

Temporal variation of genetic composition in Atlantic salmon populations from the Western White Sea Basin: influence of anthropogenic factors?

BackgroundStudies of the temporal patterns of population genetic structure assist in evaluating the consequences of demographic and environmental changes on population stability and persistence. In this study, we evaluated the level of temporal genetic variation in 16 anadromous and 2 freshwater salmon populations from the Western White Sea Basin (Russia) using samples collected between 1995 and 2008. To assess whether the genetic stability was affected by human activity, we also evaluated the effect of fishing pressure on the temporal genetic variation in this region.ResultsWe found that the genetic structure of salmon populations in this region was relatively stable over a period of 1.5 to 2.5 generations. However, the level of temporal variation varied among geographical regions: anadromous salmon of the Kola Peninsula exhibited a higher stability compared to that of the anadromous and freshwater salmon from the Karelian White Sea coast. This discrepancy was most likely attributed to the higher census, and therefore effective, population sizes of the populations inhabiting the rivers of the Kola Peninsula compared to salmon of the Karelian White Sea coast. Importantly, changes in the genetic diversity observed in a few anadromous populations were best explained by the increased level of fishing pressure in these populations rather than environmental variation or the negative effects of hatchery escapees. The observed population genetic patterns of isolation by distance remained consistent among earlier and more recent samples, which support the stability of the genetic structure over the period studied.ConclusionsGiven the increasing level of fishing pressure in the Western White Sea Basin and the higher level of temporal variation in populations exhibiting small census and effective population sizes, further genetic monitoring in this region is recommended, particularly on populations from the Karelian rivers.

Spatial and temporal variation in population trends in a long‐distance migratory bird

AbstractAim Over the past three decades, evidence has been growing that many Afro‐Palaearctic migratory bird populations have suffered sustained and severe declines. As causes of these declines exist across both the breeding and non‐breeding season, identifying potential drivers of population change is complex. In order to explore the roles of changes in regional and local environmental conditions on population change, we examine spatial and temporal variation in population trajectories of one of Europe’s most abundant Afro‐Palaearctic summer migrants, the willow warbler, Phylloscopus trochilus.Location Britain and Ireland.Methods We use national survey data from Britain and Ireland (BBS: BTO/RSPB/JNCC Breeding Bird Survey and CBS: BWI/NPWS/Heritage Council Countryside Breeding Survey) from 1994 to 2006 to model the spatial and temporal variation in willow warbler population trends.Results Across Britain and Ireland, population trends follow a gradient from sharp declines in the south and east of England to shallow declines and/or slight increases in parts of north and west England, across Scotland and Ireland. Decreasing the spatial scale of analysis reveals variation in both the rate and spatial extent of population change within central England and the majority of Scotland. The rates of population change also vary temporally; declines in the south of England are shallower now than at the start of the time series, whereas populations further north in Britain have undergone periods of increase and decline.Main conclusion These patterns suggest that regional‐scale drivers, such as changing climatic conditions, and local‐scale processes, such as habitat change, are interacting to produce spatially variable population trends. We discuss the potential mechanisms underlying these interactions and the challenges in addressing such changes at scales relevant to migratory species.

Spatial and Temporal Variation in the Population Dynamics of the Intertidal Amphipod Corophium Volutator in the Upper Bay of Fundy, Canada

The scale of variation in population densities and other demographic variables is an important consideration in the design and interpretation of experiments and sampling programs. Here, we studied spatial and temporal variation in populations of Corophium volutator, an intertidal amphipod that is the most abundant macro-invertebrate on mudflats in the upper Bay of Fundy, Canada. Variables that were quantified included density (peaked in mid-summer at |$10,000{\text{s per m}}^2$|⁠), proportion juvenile (an index of population structure), sex ratio (female-biased throughout the year), proportion of females that were ovigerous (reproduction occurs between May and August), and fecundity (number of embryos per female). We studied populations at 4 different sites, i.e., separate mudflats, for 1–2 years, and estimated variance components at 3 spatial scales: metres (samples), 100s of metres (transects) and many kilometres (mudflats). Population density exhibited low variation between years (⁠|$\lt 10\%$| of the random variation), but showed high variation at our smallest and largest spatial scales (45% between samples, 2% between transects, and 40% between mudflats), i.e., the distribution of C. volutator within a mudflat was aggregated at the scale of metres, but not at that of |$100{\rm{s}}$| of metres. Thus, relatively few transects, but many samples per transect, are required for good representation of density on a mudflat. Fecundity was similar between mudflats, but proportion juvenile, sex ratio, and proportion of ovigerous females were strongly affected by site or the interaction between month and site (⁠|$> 60\%$| of the random variation in each case). The high variation observed between mudflats for most demographic variables demonstrates that several control sites are necessary for measuring natural variation, a critical consideration in studies of environmental impacts.

Temporal Variation in Trout Populations: Implications for Monitoring and Trend Detection

AbstractWe summarized the temporal variation in populations of inland trout Salmo, Salvelinus, and Oncorhynchus spp. from streams in North America and determined the statistical power to detect trends over time. The coefficients of variation in abundance averaged 49% (SD = 27%; range = 15‐108%) over time for all ages of trout. Temporal variation was lower when more age‐classes were monitored, but whether abundance or biomass was more variable differed among populations. Detecting population trends was difficult when using the traditional α = 0.05 criterion. For example, detecting a 5% annual decline with good power (1 ‐ β ≥ 0.80) would require about 20 years if only one site were monitored. Even when α was relaxed to 0.20, 15 years were required to detect a 5% annual decline when the variation was average. Using a network of sites improved the ability to detect changes: A 5% annual decline at α = 0.05 could be detected in 10 years when 30 sites were monitored. For high‐value populations, it may require relaxing α to ensure that declines are detected, even if this increases the risk of claiming change when none has occurred and thus undertaking unnecessary management action. For example, a 5% annual decline could be detected with good power (≥0.80) in 8 years when a network of 30 sites is monitored at α = 0.20. Thus, biologists should monitor the least‐variable component of a population, monitor a network of sites, and increase α for species of concern to ensure that real population trends are detected. Estimates of trend parameters (and their uncertainty) should be considered in addition to whether or not a statistical test for trend is significant. A pilot study or existing data can help estimate the variation that is typical of the population(s) to be monitored, determine whether trends can be reliably detected, and identify how much risk needs to be incurred to detect trends.

Variation in the Geographic and Temporal Distribution of Microphallus turgidus (Trematoda: Microphallidae) in Grass Shrimp (Palaemonetes spp.) on Tidal Rivers in Southeast Georgia, U.S.A

The first goal of this study was to measure geographic variation in the abundance of Microphallus turgidus in the grass shrimp Palaemonetes pugio and to determine whether salinity at collection localities and parasite abundance are related. To do so, grass shrimp were collected at multiple localities along the Altamaha and Ogeechee rivers that varied in salinity from oligo- to polyhaline. We found a positive linear relationship between salinity and mean parasite abundance. The second goal of the study was to measure temporal variation in populations of M. turgidus in the grass shrimp P. pugio and Palaemonetes vulgaris to determine whether a relationship between temporal changes in parasite population size and variation in salinity or water temperature exists. To do so, grass shrimp were collected twice each season over the course of approximately 2.5 yr at 1 locality each on 3 tidal rivers in southeast Georgia: the Ogeechee, Broro, and Altamaha rivers. Variation between seasons in the abundance of M. turgidus in P. vulgaris was not significant. In P. pugio collected at the Altamaha and Ogeechee river localities, parasite abundance and, to some extent, parasite prevalence varied over the course of the sampling period. Correlation between water temperature and parasite abundance in P. pugio shrimp from both the Altamaha and Ogeechee river collection localities and between salinity and parasite abundance at the Altamaha River locality was slight but significantly positive. Neither relationship was observed in P. vulgaris shrimp. The results provide evidence that geographic differences in salinity might explain some of the variation in parasite abundance from one locality to another and that temporal variation in water temperature and, to some extent, salinity might also affect M. turgidus populations in P. pugio.

Recruitment rates exhibit high elasticity and high temporal variation in populations of a short‐lived perennial herb

Empirical studies for different life histories have shown an inverse relationship between elasticity (i.e. the proportional contribution to population growth rate) and temporal variation in vital rates. It is accepted that this relationship indicates the effect of selective pressures in reducing variation in those life‐history traits with a major impact on fitness. In this paper, we sought to determine whether changes in environmental conditions affect the relationship between elasticity of vital rates and their temporal variation, and whether vital rates with simultaneously large elasticity and temporal variation might represent a characteristic life‐history strategy. We used demographic data on 13 populations of the short‐lived Hypericum cumulicola over 5–6 years, in three time‐since‐fire classes. For each population of each time‐since‐fire, we computed the mean matrix over years and its respective elasticity matrix, and the coefficients of variation in matrix entries over study years as an estimate of temporal variability. We found that mean elasticity negatively significantly correlated with temporal variation in vital rates in populations (overall eight out of 13) included in each time‐since‐fire. However, seedling recruitment exhibited both high elasticity and high temporal variation in almost all study populations. These results indicated that (1) the general relationship between elasticity and temporal variation in vital rates was not modified by environmental changes due to time‐since‐fire, and (2) high elasticity and high temporal variation in seedling recruitment in H. cumulicola is a particular trait of the species' life history. After seed survival in the soil seed bank, seedling recruitment represents the most important life‐history trait influencing H. cumulicola population growth rate (and fitness). The high temporal variability in seedling recruitment suggests that this trait is determined by environmental cues, leading to an increase in population size and subsequent replenishment of the seed bank in favorable years.

Evaluation of Antemortem Sampling to Estimate Chronic Wasting Disease Prevalence in Free-Ranging Mule Deer

We conducted a field study to evaluate tonsillar biopsy immunohistochemistry (IHC) as a tool for diagnosing chronic wasting disease (CWD) in live, free-ranging mule deer (Odocoileus hemionus) and estimating CWD prevalence. Initially, we evaluated and refined techniques for collecting tonsillar biopsies from mule deer. Using a simple mouth gag and a 6-mm biopsy forceps, and taking the biopsy starting at the rostral rim of the tonsillar sinus, we obtained 155/161 (96%) samples that yielded ≥1 lymphoid follicle. To compare antemortem and postmortem survey techniques and assure biopsy-based estimates would not substantially underestimate true prevalence, we examined tonsillar biopsies from 161 free-ranging mule deer from 2 populations where CWD is endemic. We then calculated prevalence (p b ) and compared this to prevalence (p h ) estimated from tonsil samples from 161 deer harvested or culled in spatial and temporal proximity to our study areas; we considered the latter a close approximation of true prevalence. Biopsy-based prevalence estimates exceeded prevalence estimated by tonsillar IHC of samples from harvested or culled deer. Although 95% CIs for p h - p b included 0 for area-specific estimates, biopsy-based estimates were ≥3 times higher than harvest-based estimates in both study areas. Moreover, when data from both study areas were combined, p h (= 0.025) was lower than p b (= 0.081) and the 95% CI for p h - p b (-0.104 to -0.007) did not include 0. Observed differences in prevalence most likely reflected spatial or temporal variation in populations (or subpopulations) of deer sampled. Tonsillar biopsy IHC appears to be reliable for detecting CWD infections in live mule deer and estimating prevalence in affected populations, thereby representing a new tool with potential utility in CWD management, particularly in areas where harvest-based sampling is infeasible.

SPATIALLY AND TEMPORALLY PREDICTABLE FISHCOMMUNITIES ON CORAL REEFS

Spatial and temporal variation in the distribution and abundance of site-attached fish species inhabiting small, isolated patches of coral reef has been attributed to variability in larval recruitment. However, the relative importance of settlement and postsettlement processes in determining the structure of fish communities in general, i.e., including non-site-attached species inhabiting large sections of contiguous reef, remains to be determined. Here, we examine the degree of spatial and temporal variation in community structure and population density of fish inhabiting sections of coral reef varying in size and connectivity. To investigate spatial variability in fish community structure and population density, we surveyed 36 sites on contiguous reef and 39 patch-reef sites varying in size and isolation from neighboring patches. Ordination and regression analyses indicated that the structure of fish assemblages inhabiting contiguous reef varied predictably along habitat gradients. In contrast, intrinsic habitat characteristics, such as the shelter availability and the composition of the substratum, were apparently unrelated to the structure of fish assemblages on patch reefs. For sites on contiguous reef, multiple regression models explained a significant proportion of spatial variation in the population density of 10 site-attached and vagile species (including 90% of variation in the density of Pomacentrus moluccensis, a site-attached damselfish). For patch-reef sites, models of spatial variation in population density were significant for six species, five of which were not site attached. The overall pattern across most species was that patch-reef models were characterized by a reduced r2 relative to corresponding models of contiguous-reef populations, but the reduction was substantially less for vagile species than for site-attached species. Ordination analysis of temporal variability in community structure over two years suggested that none of the fish communities at the sites examined was in a consistent state of community succession. For most sites, community structure varied randomly over time, although at some sites, the structure of resident fish communities tended towards a stable position in multivariate community space. Across all sites, temporal change in community structure was significantly higher during periods of recruitment than at other times of the year, although there was little evidence to suggest that recruitment was the sole source of temporal variation. At most sites, the structure of fish assemblages fluctuated considerably during nonrecruitment periods. Patterns of temporal variation in the population density of four site-attached species indicated that population increases corresponding with pulses of recruitment were modified by postsettlement processes. For site-attached and moderately vagile species, overall temporal variability in assemblage structure increased significantly as sites became smaller and more isolated. Temporal variability in assemblages of highly vagile species was unrelated to survey area and connectivity. Overall, the results of the analyses of spatial and temporal variability in fish community structure suggest that species' vagility and reef connectivity strongly influence the relative importance of recruitment and postrecruitment processes in determining local population density. Individuals of highly vagile species are able to move among isolated patches in response to habitat preferences or resource availability. Conversely, the continuous shelter provided by contiguous reef may allow sedentary species to migrate to more favorable areas. We suggest that for many fish species, including vagile species on patchy reef and site-attached species on contiguous reef, patterns in distribution and abundance established at recruitment are modified by postsettlement migration, which enhances the relationship between population density and habitat structure. Thus, while recruitment patterns may explain much of the spatial and temporal variation in populations of site-attached fish on small, isolated patch reefs, this result cannot necessarily be extrapolated to fish communities inhabiting large sections of contiguous reef.

Spatial and temporal variation in populations and community of ectoparasites on young snapper, Pagrus auratus (Bloch &amp;amp; Schneider) (Sparidae), from the wild and captivity at Port Hacking, Sydney, Australia

Snapper in both the estuary (0+, 1+ age classes) and from offshore reefs (1+, 2+, 3+ age classes) at Port Hacking, NSW, were infested with the monogeneans Lamellodiscus pagrosomi, Anoplodiscus cirrusspiralis and Bivagina pagrosomi and the copepods Unicolax chrysophryerzus, Pseudoeucanthus australiensis, Hatschekia pagrosomi, Clavellopsis sargi and Lernanthropus atrox; offshore snapper also had the monogenean Choricotyle australiensis and the copepods Caligus spp. and Lepeophtheirus sekii. Most species had a higher prevalence, but not intensity, on offshore fish. Season was not a significant factor for most infrapopulations. Species richness, number of parasites and diversity were greater on offshore fish and differed among estuary samples but not offshore samples. Estuary infracommunities were dominated by L. pagrosomi (mainly 1+) and B. pagrosomi (mainly 0+); C. sargi and L. atrox dominated when richness was low. Offshore infracommunities were dominated by H. pagrosomi except in winter when L. pagrosomi was dominant, possibly owing to movement of estuary fish to offshore reefs. Captivity in experimental cages in the estuary resulted in transient increases in A. cirrusspiralis, B. pagrosomi and Benedenia sekii. Lamellodiscus pagrosomi increasingly dominated all samples and infracommunities. Neither condition factor nor stocking density had a significant influence on infestation.

Temporal Variation in Populations of the Marine Isopod Excirolana: How Stable are Gene Frequencies and Morphology?

Temporal Variation in Populations of the Marine Isopod Excirolana: How Stable are Gene Frequencies and Morphology?