Source-sink dynamics within a complex life history.

In marine systems, adult populations confined to isolated habitat patches can be connected by larval dispersal. Source-sink theory provides effective tools to quantify the effect of specific habitat patches on the dynamics of connected populations. In this paper, we construct the next-generation matrix for a marine metapopulation and demonstrate how it can be used to calculate the source-sink dynamics of habitat patches. We investigate the effect of environmental variables on the source-sink dynamics and demonstrate how the next-generation matrix can provide useful biological insight into transient as well as asymptotic dynamics of the model.

Patch formation is common in grazed grasslands but the mechanisms involved in the formation and maintenance of patches are not clear. To increase our knowledge on this subject we examined possible reasons for patch formation and the influence of management on changes between patch states in three experiments in native pasture communities in the Crows Nest district, south‐east Queensland. In these communities, small‐scale patches (tall grassland (dominated by large and medium tussock grasses), short swards (dominated by short tussock grasses and sedges), and lawns (dominated by stoloniferous and/or rhizomatous grasses)) are readily apparent. We hypothesized that the formation of short sward and lawn patches in areas of tall grassland was due to combinations of grazing and soil fertility effects. This was tested in Experiment 1 by applying a factorial combination of defoliation, nutrient application and transplants of short tussock and stoloniferous species to a uniform area of tall grassland. Total species density declined during the experiment, was lower with high nutrient applications, but was not affected by defoliation. There were significant changes in abundance of species that provided support for our hypotheses. With light defoliation and low nutrients, the tall grassland remained dominated by large tussock grasses and contained considerable amounts of forbs. With heavy defoliation, the pastures were dominated by medium tussock grasses and there were significant decreases in forbs and increases in sedges (mainly with low nutrients) and stoloniferous grasses (mainly with high nutrients). Total germinable seed densities and those of most species groups were significantly lower in the heavy defoliation than the light defoliation plots. Total soil seed numbers were not affected by nutrient application but there were fewer seeds of the erect forbs and more sedge seeds in plots with high nutrients. The use of resting from grazing and fire to manage transitions between patches was tested. In Experiment 2, changes in species density and abundance were measured for 5 years in the three patch types with and without grazing. Experiment 3 examined the effects of fire, grazing and resting on short sward patches over 4 years. In Experiment 2, total species density was lower in lawn than short sward or tall grassland patches, and there were more species of erect forbs than other plant groups in all patch types. The lawn patches were originally dominated by Cynodon spp. This dominance continued with grazing but in ungrazed patches the abundance of Cynodon spp. declined and that of forbs increased. In the short sward patches, dominance of short tussock grasses continued with grazing but in ungrazed plots their abundance declined while that of large tussock grasses increased. The tall grassland patches remained dominated by large and medium tussock species. In Experiment 3, fire had no effect on species abundance. On the grazed plots the short tussock grasses remained dominant but where the plots were rested from grazing the small tussock grasses declined and the large tussock grasses increased in abundance. The slow and relatively small changes in these experiments over 4 or 5 years showed how stable the composition of these pastures is, and that rapid changes between patch types are unlikely.

Ecosystem engineers, organisms that modify the environment, have the potential to dramatically alter ecosystem structure and function at large spatial scales. The degree to which ecosystem engineering produces large‐scale effects is, in part, dependent on the dynamics of the patches that engineers create. Here we develop a set of models that links the population dynamics of ecosystem engineers to the dynamics of the patches that they create. We show that the relative abundance of different patch types in an engineered landscape is dependent upon the production of successful colonists from engineered patches and the rate at which critical resources are depleted by engineers and then renewed. We also consider the effects of immigration from either outside the system or from engineers that are present in non‐engineered patches, and the effects of engineers that can recolonize patches before they are fully recovered on the steady state distribution of different patch types. We use data collected on the population dynamics of a model engineer, the beaver, to estimate the per‐patch production rate of new colonists, the decay rate of engineered patches, and the recovery rate of abandoned patches. We use these estimated parameters as a baseline to determine the effects of varying parameters on the distribution of different patch types. We suggest a number of hypotheses that derive from model predictions and that could serve as tests of the model.

Recently, Adler et al. (1984) studied the population dynamics of the meadow jumping mouse, Zapus hudsonius, in Massachusetts. As is typical of contemporary capture-recapture studies on small mammals, they used enumeration estimates of population size and survival despite the known biases of these estimators (Jolly and Dickson, 1983; Nichols and Pollock, 1983). Adler et al. (1984:390) noted that of density and survival rate during the active season for Zapus hudsonius in our study population were considerably lower than those obtained by Nichols and Conley (1982). They also compared estimates of 7 demographic for 3 species trapped on their grids: Z. hudsonius, Peromyscus leucopus, and Microtus pennsylvanicus. They found substantial differences between estimates for Z. hudsonius and the other 2 species. For example, the parameter they termed overall survival (14-day rate) was estimated at 0.13 and 0.09 for Zapus males and females, respectively, and 0.73 and 0.78 for Microtus males and females (Adler et al., 1984:389). On our Michigan study area, W. Conley and I found very similar point estimates of weekly survival probability for these 2 species (0.84 for Zapus, 0.89 for Microtus; Nichols and Conley, 1982), and these estimates did not differ significantly. In this note I do not argue that the apparent interspecific differences reported by Adler et al. (1984) are nonexistent. It may well be that such differences did exist on their study area. Instead, I point out that enumeration estimates are especially inappropriate for such interspecific comparisons and that they cannot be used to draw reasonable inferences about the underlying parameters of interest. This inappropriateness results largely from the fact that enumeration estimators estimate complicated functions of survival and capture probabilities (Nichols and Pollock, 1983) and that different species are often likely to have different capture probabilities. The relevance of capture probability to this argument leads to a second point, which involves the inappropriateness of an estimator for trappability that appears in Adler et al. (1984) and throughout the small mammal literature. The expected value of the enumeration survival rate estimator for capture period i, includes the survival and capture probabilities for every capture period subsequent to i in the entire experiment (see Nichols and Pollock, 1983: eq. 6). Because of this dependence on capture probability, 2 studied populations with identical survival probabilities but different capture probabilities would be expected to yield different enumeration survival estimates. Numerical examples of this problem appear in Figs. 1D and 1E of Nichols and Pollock (1983). These 2 examples show enumeration survival estimates for a single population with constant true survival over 12 capture periods. The difference between the survival estimates for periods with high (0.7) and low (0.3) capture probabilities exemplifies the problem that exists with interspecific comparisons in which the species do not have equal capture probabilities. Even if true survival probabilities are equal, the species with the lower capture probabilities will have lower enumeration survival estimates. W. Conley and I found substantial differences in the Jolly-Seber capture probability estimates for Z. hudsonius and M. pennsylvanicus trapped at the same times on the same grid (Table 1). Estimates for Zapus were consistently lower than those for Microtus until mid-September. We speculated that the crimped oats bait may have been especially attractive during the period of rapid weight gain preceding hibernation, resulting in the high Zapus capture probabilities in September. In any case, these differences in capture probability would have caused problems if we had used enumeration estimates to compare these 2 species. Enumeration estimates of population size and survival rate would have been biased low for both species, but the absolute value of the relative bias would have been greater for Zapus because of the lower capture probabilities. Thus, even if survival rate was similar for the 2 species, as was the case in our study, the enumeration estimate would have been lower for Zapus. Five of the 7 parameter estimates used in the interspecific comparisons of Adler et al. (1984) are functions of capture probability. Any differences between estimates for the different species may then reflect either true differences in the parameter of interest or differences in capture probability. For 3 of these estimators, average density, overall survival, and transiency rate, the effects of differences in capture probability 590 Vol. 67, No. 3

Models that combine seed demography and forest dynamics to predict seed densities in forest patches of different disturbance ages are proposed. Two models are derived from a generalized Lefkovitch model with immigration. The first model assumes constant seed rain; the second one considers seed rain as a function of the forest mosaic configuration that changes according to a Markov-chain process. This theoretical framework was used to analyze data for the pioneer tree Cecropia obtusifolia at Los Tuxtlas rain forest. Our first model suggests that despite low soil-seed survival rates, high seed densities in all patch types in a forest mosaic may be explained by the abundant seed rain typical of pioneer species. We found that an abundant seed rain to all patches enables the regeneration of this species despite high seed predation and pathogen attack rates in the soil. Analysis of the second model suggests that increased gap formation in sites 2-35 yr since disturbance seems to alter seed availability of pioneers and patch dynamics less than an equal increase in gap formation in mature patches (>35 yr since disturbed). Extensive deforestation that alters seed-rain regimes will prevent regeneration of secondary species such as C. obtusifolia that have fast seed-bank turnover rates. A comparison with previous works calls for more quantitative studies on the input and loss dynamics of soil seeds in different patches for particular tropical species.

This paper examines the effect of tax cuts policy on firm survival risk. We analyze a panel data of China’s listed companies over the period 20082021 based on two different techniques: Kaplan-Meier survival estimator and the Cox proportional hazards model. Our findings reveal that the tax cuts policy has positive and significant effect on improving firms’ survival probabilities. Moreover, compared with the income tax cuts, the value-added tax cuts play a more effective role on improving firms’ survival probability. By dividing firm locations into different regions, we also find that the tax cuts policy exerts a positive influence on firms’ survival probabilities in eastern region, while the positive effect in the central and western regions is relatively weaker. From the perspective of profitability heterogeneity, the results show that the beneficial effect from tax cuts policy on firm survival is more pronounced for firms with weaker profitability.

Dynamics of hardwood patches in a conifer matrix: 54 years of change in a forested landscape in Coastal Oregon, USA

Many capture-recapture studies on adult dragonflies have found male-biased sex ratios. However, few have estimated survivorship of males and females separately from data on frequency of recaptures in the field. Even when daily survival and capture probabilities are estimated separately, controversies can arise on whether sex biases in local survival are to be attributed to mortality or permanent emigration from the study site. The knowledge of male and female movements, assessed on an appropriate scale (i.e., within and outside the breeding site), can help address this issue. In this paper, we performed a 4-yr capture-recapture study of two Libellula fulva Müller populations in northwest Italy. Cormack-Jolly-Seber models were used to get unbiased estimates of demographic parameters (daily survival and capture probabilities, sex ratio, mean life span, and population size). Movement parameters were measured directly by georeferencing encounters. Moderate differences in survival, with males surviving better than females, were found in one population and not in the other, suggesting that these differences are not an inherent characteristic of the species. In the population with lower female survival, females were not more vagile than males, thus indicating their lower survival was caused by actual mortality rather than to emigration. In the population with no survival differences between males and females, marked males outnumbered females, but estimated sex ratios were approximately 1:1 or female biased. Therefore, raw field data were misleading because they led to underestimates of the more elusive sex and overestimates of the more detectable one (males). Survival and movement differences detected in the two populations are discussed in the framework of local environmental and demographic factors.

Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3–60 km2 and long-term average densities ranging from 0.335–0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to competition for thermal refugia in larger main stems. It also is likely that source-sink dynamics and dispersal from small headwater habitats may partially influence brook trout population dynamics in the main stem.

Study on the Impact of Antioxidant on the FLASH Effect With 6 MeV X-Ray

Overall impacts of targeted conservation interventions on population growth rate (λ) will depend on within‐year and among‐year variation in exposure of target individuals to interventions, and in intervention efficacy in increasing vital rates of exposed individuals. Juvenile survival is one key vital rate that commonly varies substantially within and among years, and consequently drives variation in λ. However, within‐year, among‐year and overall impacts of targeted interventions on population‐wide survival probabilities of potentially mobile juveniles are rarely quantified, precluding full evaluation and evidence‐based refinement of interventions. We applied multi‐state mark–recapture models to 8 years of ring–resighting data from a threatened red‐billed chough Pyrrhocorax pyrrhocorax population to quantify within‐year and among‐year variation in juvenile exposure to a targeted intervention of supplementary feeding and parasite treatment, and to estimate efficacy in increasing juvenile survival probability. We then combined and up‐scaled these estimated effects to evaluate the impact of the 8‐year intervention on overall population‐wide survival probability and resulting population size. High proportions of surviving juveniles (>70%) were exposed to the intervention across the annual biological cycle in all years. Exposure was associated with higher short‐term survival probabilities through the full annual cycle. Consequently, management increased estimated population‐wide annual juvenile survival by approximately 0.14. However, such effects were only evident in cohorts with low overall annual survival. Population models projected that these impacts on annual juvenile survival substantially reduced population decline, such that population size at the end of the 8‐year intervention was approximately double that without management. Synthesis and applications. Our results show how complex patterns of within‐year and among‐year variation in exposure and efficacy of targeted conservation interventions can arise and scale up to affect population‐level outcomes. We demonstrate overall positive effects of a joint supplementary feeding and parasite treatment intervention on the focal chough population, but also highlight potential routes to improve efficacy, for example, through more precise targeting of interventions and agricultural management actions in the context of among‐year variation in environmental conditions.

Primary sclerosing cholangitis (PSC) is an immune-related cholangiopathy without treatment options beyond liver transplantation. The gut-liver axis, especially the role of gut microbes, has emerged as a crucial pathway contributing to PSC pathogenesis. Recent research has revealed Enterococcus (E.) faecalis and its virulence factor cytolysin to increase mortality risk in patients with alcohol-associated hepatitis. Thus, we studied the role of enterococci, particularly E. faecalis and its virulence factor genes cytolysin and gelatinase, in faecal samples from patients with PSC. To assess the relevance of Enterococcus species, we performed 16S rRNA gene amplicon analysis in faecal samples from 60 patients with PSC. We validated our findings by qPCR of faecal microbial DNA in an extended cohort of 105 patients with PSC, 104 patients with inflammatory bowel disease (IBD) and 68 healthy subjects. High-throughput 16S rRNA amplicon analysis revealed an increased relative abundance of enterococci in PSC patients compared with healthy controls and IBD patients, respectively, (p < 0.0001). PSC patients with high enterococci abundance had a decreased probability of transplant-free survival (p = 0.028). E. faecalis and its virulence factors cytolysin and gelatinase were more abundant in patients with PSC. Higher faecal cytolysin was associated with lower overall survival (p = 0.04), while survival was independent of gelatinase levels. Our data highlight the association of E. faecalis and faecal cytolysin with lower survival in patients with PSC. These data should prompt further research into the pathogenic role of cytolysin-positive E. faecalis, and to explore its role as a potential therapeutic target.

Background/Question/Methods: Habitat heterogeneity has long been shown to be a driver of species richness in ecological systems. Untangling which aspects of habitat heterogeneity are important to a specific system, however, can be more complicated. Habitat heterogeneity operates at both spatial and temporal scales, from micro- to global levels, and can be driven intrinsically or extrinsically. Additionally, these distinctions are not mutually exclusive. Using 26 years of rodent abundance time series data from the Portal project, an experimental site in southeastern Arizona, we ask how both spatial and temporal habitat heterogeneity affect species and how they view the landscape. The Portal project consist of 24 plots with three different treatments: full rodent access (controls), kangaroo rat ( Dipodomys sp. ) exclosures, and rodent removals. With multiple treatment types, the system essentially establishes multiple patches within a more-or-less continuous landscape. In the mid-1990s, a novel competitor, Chaetodipus baileyi , colonized at the site; recently, however, C. baileyi has all but disappeared from the system. Here, we investigate how the arrival and disappearance of C. baileyi influences how an abundant smaller congeneric, C. penicillatus , views the patchy landscape. Results/Conclusions: Our results demonstrate that C. penicillatus’s view of the landscape has, in fact, changed in response to the arrival and subsequent decline of C. baileyi . Initially, C. penicillatus was found primarily on kangaroo-rat exclosures, as Dipodomys were its main competitors. With the invasion of C. baileyi in the mid-1990s, C. penicillatus became disproportionately more abundant on control plots. Population metrics of C. penicillatus , including immigration of new individuals, apparent survival, and transition probability between plot types, were all affected by the arrival of C. baileyi . Previous research has shown that the arrival of C. baileyi also had profound effects on ecosystem functioning in the kangaroo rat exclosures, which had previously never greater than 33% of the energy use by Dipodomys sp . on control plots. Our results suggest that ecosystem function has decreased through time but not dropped back to pre-invasion levels, suggesting that ecosystem functioning may have been affected by these shifting views of the landscape. Together, our results suggest that even though all patches are experiencing the same extrinsic environment, the intrinsic heterogeneity of patches—in this case, driven by differences in the dominant competitor in the patch types—can influence a species’ patch selection.

Costimulatory molecules such as lymphocyte function-associated antigen (LFA)-1 (CD11a), LFA-3 (CD58), intercellular adhesion molecule (ICAM)-1 (CD54), neuronal cell adhesion molecule (NCAM) (CD56), B7-1 (CD80), or B7-2 (CD86) are important regulatory elements in healthy immunological cascades, but their role in acute myeloid leukemia (AML) has only been rarely investigated. We studied their expression on mononuclear bone marrow (BM) cells from 105 patients with AML at initial diagnosis and evaluated their prognostic significance. Fluorescence-activated cell sorter (FACS) analyses were performed using antibodies directly conjugated with fluorescein. A BM sample was considered positive if more than 20% of the cells in the blast containing gate expressed the respective marker. The surface expression of CD11a (27 of 29 cases positive with an average of 71% positive blasts; 27(+)/29, 71%), CD54 (23(+)/33, 37%), CD56 (24(+)/93, 20%), CD58 (29(+)/29, 95%), CD80 (13(+)/28, 30%), and CD86 (19(+)/29, 39%) was measured. The expression of these markers in different French-American-British (FAB) classification types (M0-M5) was heterogeneous, except for CD56, which showed a higher proportion of positive cells in monocytic subtypes of AML. In addition, cases with a "poor risk" karyotype as well as patients succumbing to "early death" after double induction therapy according to the AML Cooperative Group (CG) protocol were characterized by a high expression of CD56. Relapse-free survival analyses demonstrated that patients with more than 8% CD56(+) cells in the BM relapsed significantly sooner. CD54 was preferentially expressed in AML M4(eo) and in addition in "favorable" cytogenetic risk groups and in cases that had responded to AML-CG therapy. Only very high proportions (>60%) of CD54(+) cells were associated with a lower probability for relapse-free survival. CD80 and CD86 expressions were similar in all FAB types. Patients who had responded to AML-CG therapy showed higher CD80 proportions and lower CD86 proportions compared to the "nonresponder" group. Whereas cases with more than 15% CD80(+) cells had a significantly lower probability for relapse-free survival, only cases with more than 65% CD86(+) were characterized by a significantly lower probability for relapse-free survival. Expression profiles of CD11a and CD58 were not associated with specific FAB types or prognostically relevant groups. We can conclude: (1) Expression of costimulatory molecules in AML is very variable. This reflects the great diversity of immunophenotypes in AML. (2) CD56 is mainly expressed in monocytic subtypes of AML. CD56(+) subtypes of AML seem to be a separate entity with a worse prognosis independent of the karyotype. (3) High expression of some costimulatory molecules correlates with a worse prognosis concerning relapse-free survival times.

Evaluation of Recurrence Predictors and Survival Probability After Liver Transplantation for Hepatocellular Carcinoma: Analysis From a Single Center.