Variation In Annual Reproductive Success Research Articles

No short-term effects of climate change on the breeding of Rock Ptarmigan in the French Alps and Pyrenees

In the last decades, the effects of climate warming have been particularly marked in high mountain areas. High-altitude species adapted to cold temperatures are consensually held to be particularly vulnerable to climate warming. Among these species at risk, alpine birds like the Rock Ptarmigan (Lagopus muta) are expected to exhibit a strong negative response, particularly at the southern margins of their ranges in the northern hemisphere. In this study, conducted from 1998 to 2011, we investigated whether variations in the local climate affected the breeding biology of Rock Ptarmigan in the French Alps and Pyrenees. The median hatching date did not significantly advance in either massif, suggesting that Rock Ptarmigan did not breed earlier during this period. The date of snowmelt and spring temperatures influenced the onset of breeding but not consistently in both sites. In the Alps, the median hatching date was significantly correlated with the date of snowmelt, but this correlation was less clear in the Pyrenees. Unlike woodland grouse which inhabit lower elevations, the onset of breeding in Rock Ptarmigan may be related to both date of snowmelt and spring temperatures. Reproductive success varied greatly over the years and among sites. On average, the number of young per adult in the Pyrenean population was greater than that recorded in the two populations in the Alps. A significant positive trend of reproductive success over the period of 2000–2009 was detected in the Pyrenees but not in the Alps. The model that best explained annual variation in reproductive success included the additive effects of site, date of total snowmelt and rainfall after hatching. The estimates from this model showed that for all sites, reproductive success was much lower when snowmelt was late, and rainfall after hatching was high. We did not detect any altitudinal changes in locations of either breeding females or nests, suggesting that the breeding habitat of the species has not shifted upward from 1998 to 2011. To conclude, although the Rock Ptarmigan is generally considered a potential sentinel species for indicating temperature-induced changes in alpine avifauna, our study did not show a short-term effect of climate change on the breeding biology of the southern populations of this species.

Ocean eddies, predator pits and bluefin tuna: implications of an inferred ‘low risk–limited payoff’ reproductive scheme of a (former) archetypical top predator

AbstractThe conventional view of the reproductive ecology of bluefin tunas (Thunnus thynnus, Thunnus orientalis, Thunnus maccoyii) leads to a conceptual paradox. Simple arithmetic yields an expectation for wide variation in annual reproductive success. However, the historical record does not support this prediction. A conclusion would seem to be that a much stronger than usual density dependence must be acting. It is here argued that this strong density dependence may likely occur within small strongly convergent segments of energetically forced ocean eddy structures. Success of the implied ecological scenario requires spawning schools of sufficient size to generate sufficiently copious reproductive product to circumvent resident predator pits, while exerting sufficient predatory loss on resident predators to facilitate this circumvention. This in turn implies existence of a dangerous ‘precipice’ in the form of self‐enhancing feedback loop, lurking unperceived beyond the range of historical experience, and a need for a particular degree of precaution in managing the exploitation of this iconic species.

Diseases and reproductive success in a wild mammal: example in the alpine chamois

Density-dependent and climatic factors affect reproduction and dynamics of wild ungulates. Parasites can also decrease reproductive success through either a direct abortive effect or a negative impact on host growth and body condition. However, few studies have investigated the effect of parasitism on fecundity of ungulates in natural conditions. We studied three bacterial infections caused by Salmonella enterica serovar Abortusovis, Chlamydophila abortus and Coxiella burnetii. These bacteria are leading causes of reproductive failure in sheep, goat and cattle, which raises the question of their influence on population dynamics of wild ungulates. A long-term study of demography and epidemiology of an alpine chamois (Rupicapra rupicapra, L.) population (Les Bauges Reserve, France) and a generalized linear modeling approach were used to analyze the reproductive success of chamois according to population density, weather conditions and the prevalence of antibodies against the three bacteria in females. This approach enabled us to identify the confounding effect of weather and parasitism on fecundity in a natural population. After accounting for density, the prevalence of antibodies against the three bacteria explained 36% of the annual variation in reproductive success, and weather conditions explained an additional 31%. This study was, to our knowledge, the first to compare the decrease in fecundity due to bacterial infections and weather conditions in a population of wild mountain ungulates.

Effect of weather on the reproductive rate of Rock Ptarmigan Lagopus muta in the eastern Pyrenees

Understanding the effects of climate on avian life history traits is essential if we wish to predict the demographic consequences of expected climatic changes. We investigated the influence of weather conditions on the reproductive success of Rock Ptarmigan Lagopus muta in the eastern French Pyrenees, one of the southernmost areas inhabited by the species. Reproductive success was estimated in early August between 1997 and 2006 by counting adults and well‐grown chicks with pointing dogs. The number of young per adult varied from 0.08 to 0.72. Using Poisson regression and Akaike's information criterion, we selected the best model explaining the effect of weather (date of snowmelt and, for both laying/incubation and post‐hatching periods, mean minimum and maximum temperatures, monthly rainfall and number of days with rain) on the proportion of young in August. Reproductive success was positively associated with early appearance of snow‐free ground, and date of snowmelt alone was the model that best explained annual variation in reproductive success. Other models, which included a negative effect of rainfall, particularly after hatching, also had some support. Hence, both pre‐laying and post‐hatching weather conditions influenced reproductive success of Rock Ptarmigan in the eastern French Pyrenees. On a continental scale, reproductive success of alpine populations of Rock Ptarmigan is consistently lower than that of northern populations. This difference in productivity may be partly correlated with climatic conditions observed along an arctic–alpine gradient, the amount and variation of rainfall being greater in southern alpine areas than elsewhere in the species’ range.

Benefits of large broods by higher chick survival and better territories in a precocial shorebird

When reproductive success is constant in one breeding phase, different tactics that increase variation in reproductive success among individuals may evolve in other phases. For instance, in shorebirds, which usually have a limited clutch size of four eggs, variation in reproductive tactics among individuals is expected either before egg-laying (e.g. diverse mating systems) or after hatching of the young (e.g. diverse parental care). In this paper, I studied the pied avocet (Recurvirostra avosetta), a shorebird with a modal clutch size of four eggs, to test whether post-hatch chick adoption as an alternative tactic can be linked to increased variation in annual reproductive success. When predation was high, naturally adopting pairs produced more filial fledglings than did pairs not adopting chicks and not losing chicks to adoption. The number of filial fledglings increased with the number of adopted young, possibly through diluting the chances of predation on filial young. Experimental chick addition did not lead to more fledged young due to low brood integrity as shown by the frequent loss of chicks from some experimental broods. When predation was low, larger broods occupied feeding territories with higher prey abundance than smaller broods, possibly due to their dominance over smaller ones. Pairs that lost chicks to adoption (donors) fledged as many filial young in their broods as did non-adopters/non-donors, whereas the total number of donors’ filial fledglings, including those raised in adopting broods, approached that of adopters. These findings show, for the first time, that post-hatch alternative reproductive tactics can lead to variation in annual reproductive success and to higher success for some pairs even in species where past adaptations limit variation in reproductive success in a certain phase of reproduction.

Combined food and predator effects on songbird nest survival and annual reproductive success: results from a bi-factorial experiment

Food and predators have traditionally been viewed as mutually exclusive alternatives when considering factors affecting animal populations. This has led to long controversies such as whether annual reproductive success in songbirds is primarily a function of food-restricted production or predator-induced loss. Recent studies on both birds and mammals suggest many of these controversies may be resolved by considering the combined effects of food and predators. We conducted a 2x2 manipulative food addition plus natural predator reduction experiment on song sparrows (Melospiza melodia) over three consecutive breeding seasons. Food and predators together affected partial clutch or brood loss, nest survival (total clutch or brood loss) and annual reproductive success. When combined, our two treatments reduced partial losses by more than expected if the effects of food and predators were independent and additive. Food and predators also interacted in their effects on nest survival since food addition significantly reduced the rate of nest predation. While annual reproductive success was highly correlated with nest predation (r2=0.71) the strength of this relationship was reinforced by the indirect effects of food addition on nest predation. A stepwise multiple regression showed that the residual variation in annual reproductive success was explained by food effects on the total number of eggs laid over the season and the combined effects of food and predators on partial losses noted above. We conclude that annual reproductive success in song sparrows is a function of both food-restricted production and predator-induced loss and indirect food and predator effects on both clutch and brood loss. We highlight the parallels between our results and those from a comparable bi-factorial experiment on mammals because we suspect combined food and predator effects are likely the norm in both birds and mammals.

Optimizing reserve expansion for disjunct populations of San Joaquin kit fox

Expanding habitat protection is a common strategy for species conservation. We present a model to optimize the expansion of reserves for disjunct populations of an endangered species. The objective is to maximize the expected number of surviving populations subject to budget and habitat constraints. The model accounts for benefits of reserve expansion in terms of likelihood of persistence of each population and monetary cost. Solving the model with incrementally higher budgets helps prioritize sites for expansion and produces a cost curve showing funds required for incremental increases in the objective. We applied the model to the problem of allocating funds among eight reserves for the endangered San Joaquin kit fox ( Vulpes macrotis mutica) in California, USA. The priorities for reserve expansion were related to land cost and amount of already-protected habitat at each site. Western Kern and Ciervo-Panoche sites received highest priority because land costs were low and moderate amounts of already-protected habitat resulted in large reductions in extinction risk for small increments of habitat protection. The sensitivity analysis focused on the impacts of kit fox reproductive success and home range in non-native grassland sites. If grassland habitat is lower quality than brushland habitat resulting in higher annual variation in reproductive success or larger home ranges, then protecting habitat at the best grassland site (Ciervo-Panoche) is not cost–efficient relative to shrubland sites (Western Kern, Antelope Plain, Carrizo Plain). Finally, results suggested that lowest priority should be given to three relatively high-cost grassland sites (Camp Roberts, Contra Costa, and Western Madera) because protecting habitat at those sites would be expensive and have little effect on the expected number of surviving kit fox populations.

Energy Constraints on Incubating Common Eiders in the Canadian Arctic (East Bay, Southampton Island, Nunavut)

Common eider ducks have a circumpolar distribution. Several populations that occur in polar areas during the summer move to northern or temperate coastal areas during winter. All eider species have delayed reproductive maturity, low rates of recruitment, and high rates of adult survival (often 15 + years). These characteristics, coupled with their gregarious nature, render eider ducks highly vulnerable to the effects of hunting, lead poisoning, contaminants, and oil pollution. Even slight reductions in adult survival rates can cause populations to decline. Low annual rates of recruitment and successive years of reproductive failure can also affect populations and slow their recovery. ... Concern within the scientific community has recently generated several conservation policy documents. These include the Circumpolar Eider Conservation Strategy and Action Plan of the Circumpolar Seabird Working Group ..., the Seaduck Joint Venture (revised North American Waterfowl Management Plan, 1999) and the Cooperative Research Strategy for Eider Ducks Breeding in Northern Canada of the Canadian Wildlife Service .... All of these documents stress the need for research and monitoring of eider ducks. Information regarding the population dynamics of common eiders breeding in the Canadian Arctic is limited and out of date .... The CWS East Bay project was established to research these issues. Research topics at the colony include predator-prey interactions, the influence of ice cover and snowmelt on nest initiation, levels of heavy metal contamination and internal parasite loads, population ecology (e.g. adult survival rates), and sources of annual variation in reproductive success. ... My individual project examines the costs of incubation among arctic common eiders: specifically, how variation in energy reserves and annual environmental conditions (e.g., temperature, precipitation) influence female incubation behaviour and reproductive success. ...

Reproductive Success and Female Survival Affect Local Population Density of Canvasbacks

Long-term data (1949-55 and 1959-80) from a canvasback (Aythya valisineria) population near Minnedosa, Manitoba suggested that breeding density was limited to ≤4.5 pairs/km 2 by annual variation in reproductive success (the local-recruitment hypothesis). We attempted to test this hypothesis by experimentally increasing reproductive success on a 15.8-km 2 study block during 1983-90. Manipulations included barrier fences to protect canvasback nests from mammalian predators and egg additions to replace canvasback eggs that had been displaced due to parasitic egg-laying by redheads (Aythya americana). We monitored breeding pair density and duckling production on the experimental study block and on an adjacent 15.8-km 2 control block using complete pair and brood counts (1983-90), nest and brood monitoring (1983-90), and roadside pair and brood surveys (1983-94). We nasal-marked pre-fledgling and adult female canvasbacks and used mark-resighting analysis to estimate juvenile survival, adult survival, and resighting probabilities. Reproductive success varied substantially among years, primarily in response to variable wetland conditions. The experimental study block had higher per capita fledging success during 6 out of 8 years (P = 0.08), but survival and resighting rates did not differ between study blocks (P = 0.28-0.80). Indices of canvasback density were similar during 1983-84, but pair populations became higher on the experimental block during 1985-90 (P 0.16). Annual changes in pair density were correlated positively with adult survival (r = 0.69, P = 0.007) and fledged ducklings/hen (r = 0.62, P = 0.02), although neither correlation remained significant when the other factor was controlled with partial correlation (P = 0.24 and 0.63). Population simulations suggested that both factors were important in affecting population changes. Management actions that enhance local breeding success or annual survival should lead to larger local breeding populations.

COOPERATIVE BREEDING IN A POPULATION OF WHITEBROWED SPARROW WEAVERS PLOCEPASSER MAHALI

SummaryThis paper reports on a three year study describing cooperative breeding and demography of a sampled population of approximately 108 colour‐marked White‐browed Sparrow Weavers in Zambia. Twenty‐seven communal groups with two to 11 individuals in a group made up this population and occupied a l km2 area of mopane woodland. Each group had only a single reproductive pair and the pair‐bond appeared strong. Non‐reproductives were generally siblings or half‐siblings and they contributed a major share of nestling feeding, nest building, intruder chasing and guarding. Groups cooperatively built nests in certain preferred trees and they maintained their nests year round. Feeding range encircled the nesting site and was used almost exclusively by the communal group.Overall population density was relatively stable, and between‐year variation in group size was significantly greater than within‐year variation. Variation in annual reproductive success among groups was high and correlated positively with size. Mortality rates for nestlings, six‐month‐olds and juveniles were not correlated significantly with group size. Frequency of disappearance for reproductives of both sexes was correlated negatively with group size.