Long-term occurrence of Hemolivia cf. mauritanica (Apicomplexa: Adeleina: Haemogregarinidae) in captive Testudo marginata (Reptilia: Testudinidae): evidence for cyclic merogony?

Blood smears from wild-caught, long-term captive tortoises, Testudo marginata, revealed the presence of gametocytes of a Hemolivia mauritanica-like hemogregarine in the erythrocytes of 72% tortoises examined. Significant parasitemia was also found in animals living several years in captivity. Experimentally infected tortoises showed no evidence of a decrease in parasitemia level more than 15 mo after infection. Morphologically, stages found in tortoises' erythrocytes were indistinguishable from those referred to by previous workers as H. mauritanica from Testudo graeca. Moreover, successful experimental transmission to Hyalomma aegyptium confirms the conspecificity with H. mauritanica. The occurrence of H. mauritanica gametocytes in tortoise living up to 8 yr in captivity is suggested to result from continuous, long-lasting cyclic merogony in tortoises' parenchymatous organs, which is an unknown phenomenon in the life cycle of Hemolivia spp.     

Studies on the growth, structure and abundance of the Mediterranean spur-thighed tortoise, Tesudo graeca in field populations

The blackness and physical appearance of Mediterranean spur-thighed tortoises ( Testudo graeca L.) are recorded in field populations. The inter-relationships between carapace and plastron length, fourth vertebral scute width and other morphometric characters are related to growth. The rear fontanelle is larger in males and the plastron length correspondingly smaller. The relationship between carapace length ( y ) in mm and body mass ( x ) in g is strongly allometric and given by y = 16.63 x ^0–34. The maximum carapace lengths recorded for male and female T. graeca graeca L. in NW. Africa are 151 and 198 mm, and for larger T. graeca ibera Pallas in W. Turkey and NE. Greece 208 and 218 mm, respectively. The growth annuli of epidermal scutes are deposited yearly until external growth ceases. The number is used to assess the age of wild animals. Tortoises can be full-grown by 19 years but some, especially slower growing ones, deposit further annuli. The biggest mean growth increments occur up to 7 years with the largest in individuals over the 5–12 year period. The proportion of immature tortoises, adult sex ratios, size and body mass structure, age distribution, annual recruitment and survivorship until full-grown, and abundance (sighting frequency) are compared in northern and southern range populations of NW. African T. g. graeca and S. Anatolian and SE. European (Thrace and Macedonia) ones of T. g. ibera. These are discussed in relation to other tortoise species.     

Culling Versus Density Effects in Management of a Deer Population

Abstract: Wildlife managers often manipulate hunting regulations to control deer populations. However, few empirical studies have examined the level of hunting effort (hunter-days) required to limit population growth and demographic effects through harvesting of females. Moreover, the relative importance of density effects on population growth has not been quantified. We reconstructed a sika deer [Cervus nippon] population over a period of 12 years (1990–2001) using age- and sex-specific harvest data. Using cohort analysis, we analyzed population dynamics, focusing on 1) the relationship between hunting effort and hunting-induced mortality rate, 2) relative contributions of hunting mortality and recruitment of yearlings to annual changes in population growth rate, and 3) annual variation in recruitment rate. Population size increased until 1998 and declined thereafter. The population growth rate changed more in response to annual changes in recruitment rate than hunting mortality rate. Temporal variation in recruitment rate was not controlled by birth rate alone; direct density dependence, intensities of hunting mortality for fawns, and for females (≥2 yr of age), which accounted for the fawn survival rate, were required as factors to explain temporal variation. Density effects on the recruitment rate were not strong enough to regulate the population within the study period; high hunting mortality, with intensive female harvesting, was necessary to prevent population growth. Hunting effort was a good predictor of the hunting mortality rate, and female harvest had a negative effect on the recruitment rate through fawn survival. We suggest that >3,500 hunter-days and prioritization of female harvesting are required to prevent increases in this deer population.     

The population increase of common guillemots Uria aalge on Skomer Island is explained by intrinsic demographic properties

The population of common guillemots Uria aalge on Skomer Island, Wales has been monitored since 1963, and in the last 30 yr has increased at an almost constant rate of 5% yr^?1. A previous attempt to model the population based on intrinsic demographic parameters estimated over just five years failed to explain the observed population increase, probably because the estimate of juvenile survival was too low. This raised the possibility that immigration fuelled the population increase. Here we use > 30 yr of detailed field observations to re‐estimate key population parameters (productivity, adult survival and juvenile survival) in order to model the population. We show that the observed rate of increase can be explained by these intrinsic parameters, and we therefore conclude that immigration is not necessary to generate the observed population growth.     

The founding of a southern elephant seal colony

The only large mainland colony of southern elephant seals (Mirounga leonina) is on Península Valdés, at 42°S, in Argentine Patagonia. Censuses of pups have been carried out regularly there since 1970, and the population grew five‐fold by 2010. Here we use Bayesian modeling tools to make rigorous estimates of the rate of population growth, r, and to estimate survival and recruitment parameters that could account for the growth, incorporating observation error across different census methods. In the 1970s, r= 8%/yr, but has slowed to <1%/yr over the past decade. Using explicit demographic models, we established that the high growth of the 1970s was consistent with adult and juvenile survival at the upper end of published values (0.87/yr adult female survival; 0.40 juvenile survivorship to age four); the decline in the rate of population growth from 1970 to 2010 can be described by density‐dependent reductions in adult and juvenile survival that fall well within published variation. Extrapolating empirical models of population growth rate backwards illustrates that the population could have been an established colony, with 100 pups born per year, between 1915 and 1945, consistent with qualitative observations prior to 1950. We conclude that the Valdés colony was founded by a few immigrants early in the 20th century and has been growing mostly by internal recruitment, with unknown density‐dependent processes causing a reduction in growth and stabilization at 15,000–16,000 pups born.     

Impact of human disturbance,density, and environmental conditions on the survival probabilities of pipistrelle bat (Pipistrellus pipistrellus)

Natural and anthropogenic disturbances can strongly impact population dynamics of species and are often responsible for zoonotic emerging infectious diseases. However, long-term studies on the demographic consequences of human disturbances are unusual. We used 6 years (1995–2000) of mark-recapture data to investigate how climatic conditions, human disturbance and density affect sex- and age-specific apparent survival probabilities of the pipistrelle bat (Pipistrellus pipistrellus, Schreber 1774) in a maternity colony. Our study demonstrated that density played an important role in population dynamics of pipistrelle bat and that its effect differed with respect to age and sex. Notably, human disturbance caused a strong decline of adult female survival, suggesting that perturbations have important consequences in bat-colony dynamics. Juvenile female survival was negatively influenced by density, being considerably lower in high densities. In contrast, juvenile and adult males were apparently not affected as they had constant survival probabilities. Although climatic factors can markedly affect population dynamics of temperate insectivorous bats, in this study, the weather conditions did not influence the survival rates of pipistrelle bats. We provide the first report that demonstrates the density-dependent effect on bat survival. That is especially relevant to better understanding of the bat-population dynamics and to evaluate the consequences of human disturbance and their potential changes in the maternity colony structure.     

Population dynamics of Clethrionomys and Peromyscus in southwestern Yukon 1973-1989

Clethrionomys rutilus and Peromyscus maniculatus occur together in the boreal forest of southwestern Yukon and we studied their population dynamics on unmanipulated live-trapping grids for 17 yr. Peromyscus showed a regular seasonal change in numbers each year with little interannual variation. Clethrionomys by comparison, showed low density fluctuations during one period (1976-1982) followed by changes in number in the next period that are consistent with a typical 3-4 yr microtine cycle. During one of two years of peak numbers adult males had unusually heavy body weights. The sexual maturation of juvenile Clethrionomys varied inversely with density. In most years Clethrionomys showed higher rates of population increase from spring to late summer than Peromyscus and this may be partly attributed to the vole's longer breeding season. Juvenile female Clethrionomys often reached sexual maturity during their first summer when population density was low but Peromyscus never matured during their first summer. Finally, there was no correlation between the two species in year to year changes in overwinter survival rates. This is the first report of a cyclic Norh American population of Clethrionomys and it underlines the need to search for hypotheses of population regulation that explain both annual and multi-annual cycles within the same population.     

Ecosystem Scale Declines in Elk Recruitment and Population Growth with Wolf Colonization: A Before-After-Control-Impact Approach

The reintroduction of wolves (Canis lupus) to Yellowstone provided the unusual opportunity for a quasi-experimental test of the effects of wolf predation on their primary prey (elk – Cervus elaphus) in a system where top-down, bottom-up, and abiotic forces on prey population dynamics were closely and consistently monitored before and after reintroduction. Here, we examined data from 33 years for 12 elk population segments spread across southwestern Montana and northwestern Wyoming in a large scale before-after-control-impact analysis of the effects of wolves on elk recruitment and population dynamics. Recruitment, as measured by the midwinter juvenile∶female ratio, was a strong determinant of elk dynamics, and declined by 35% in elk herds colonized by wolves as annual population growth shifted from increasing to decreasing. Negative effects of population density and winter severity on recruitment, long recognized as important for elk dynamics, were detected in uncolonized elk herds and in wolf-colonized elk herds prior to wolf colonization, but not after wolf colonization. Growing season precipitation and harvest had no detectable effect on recruitment in either wolf treatment or colonization period, although harvest rates of juveniles∶females declined by 37% in wolf-colonized herds. Even if it is assumed that mortality due to predation is completely additive, liberal estimates of wolf predation rates on juvenile elk could explain no more than 52% of the total decline in juvenile∶female ratios in wolf-colonized herds, after accounting for the effects of other limiting factors. Collectively, these long-term, large-scale patterns align well with prior studies that have reported substantial decrease in elk numbers immediately after wolf recolonization, relatively weak additive effects of direct wolf predation on elk survival, and decreased reproduction and recruitment with exposure to predation risk from wolves.     

Long-term trends in survival of a declining population: the case of the little owl (<Emphasis Type="Italic">Athene noctua</Emphasis>) in the Netherlands

The little owl (Athene noctua) has declined significantly in many parts of Europe, including the Netherlands. To understand the demographic mechanisms underlying their decline, we analysed all available Dutch little owl ringing data. The data set spanned 35 years, and included more than 24,000 ringed owls, allowing detailed estimation of survival rates through multi-state capture–recapture modelling taking dispersal into account. We investigated geographical and temporal variation in age-specific survival rates and linked annual survival estimates to population growth rate in corresponding years, as well as to environmental covariates. The best model for estimating survival assumed time effects on both juvenile and adult survival rates, with average annual survival estimated at 0.258 (SE = 0.047) and 0.753 (SE = 0.019), respectively. Juvenile survival rates decreased with time whereas adult survival rates fluctuated regularly among years, low survival occurring about every 4 years. Years when the population declined were associated with low juvenile survival. More than 60% of the variation in juvenile survival was explained by the increase in road traffic intensity or in average temperature in spring, but these correlations rather reflect a gradual decrease in juvenile survival coinciding with long-term global change than direct causal effects. Surprisingly, vole dynamics did not explain the cyclic dynamics of adult survival rate. Instead, dry and cold years led to low adult survival rates. Low juvenile survival rates, that limit recruitment of first-year breeders, and the regular occurrence of years with poor adult survival, were the most important determinants of the population decline of the little owl.     

Effects of density-dependence and climate on the dynamics of a Svalbard reindeer population

To determine the main factors affecting the population dynamics of Svalbard reindeer, we analysed 21 yr of annual censuses, including data on population size, recruitment rate (calves per female) and mortality (number of deaths), from the Reindalen reindeer population. In accordance with previous studies on population dynamics of Svalbard reindeer, we found large inter-annual variation in population size, mortality and recruitment rates within the study area. Population size decreased in years with low recruitment rate as well as high winter mortality and vice versa. Apparently. the fluctuations were due to both direct density-dependent food limitation and variation in winter climate associated with high precipitation and icing of the feeding range. We found no delayed density-dependence or effect of climatic conditions during summer on the population dynamics. The mortality during die-off years was mainly of calves and very old individuals, indicating that the population was more vulnerable to high die oft in years following high recruitment rate. These results suggest an unstable interaction between the reindeer population and its food supply in these predator-free environments.     

Mitochondrial haplotype diversity in the tortoise species <Emphasis Type="Italic">Testudo graeca</Emphasis> from North Africa and the Middle East

Background  

To help conservation programs of the endangered spur-thighed tortoise and to gain better insight into its systematics, genetic variation and evolution in the tortoise species Testudo graeca (Testudines: Testudinidae) was investigated by sequence analysis of a 394-nucleotide fragment of the mitochondrial 12S rRNA gene for 158 tortoise specimens belonging to the subspecies Testudo graeca graeca, Testudo graeca ibera, Testudo graeca terrestris, and a newly recognized subspecies Testudo graeca whitei. A 411-nucleotide fragment of the mitochondrial D-loop was additionally sequenced for a subset of 22 T. graeca, chosen because of their 12S gene haplotype and/or geographical origin.     

Survival estimates for the Australian sea lion: Negative correlation of sea surface temperature with cohort survival to weaning

The Australian sea lion (Neophoca cinerea) population at Seal Bay Conservation Park, South Australia, is estimated to be declining at a rate of 1.14% per breeding season. To better understand the potential causes of this decline, survival rates were examined to 14 yr of age for eight cohorts marked as pups (aged 0.17 yr) between 1991 and 2002. Apparent yearly survival rates (Φ) varied by cohort for pups from marking to weaning at 1.5 yr (Φ= 0.30–0.67). Postweaning juvenile survival (1.5–3 yr) was 0.89 and survival from 3 to 14 yr was constant (Φ female:male = 0.96:0.89). Φ of pup cohorts was negatively correlated to local sea surface temperature where the sea lions forage (SST) and was especially low for cohort 7 in 2000 (0.30). It is possible that periods of unusually warm oceanographic conditions may be limiting primary production and inhibiting maternal provisioning to pups. Pup survival to weaning is relatively low compared to other otariid species, is likely to limit recruitment, and may be contributing to the decline in pup abundance observed in the colony.     

Bottom‐up processes in a declining yellow‐footed rock‐wallaby (Petrogale xanthopus celeris) population

Populations of large herbivores are generally considered to be food limited, escaping the regulatory effects of predation through their large body size, migratory behaviour and/or the occurrence of alternate prey species. In the Australian arid and semi‐arid zones, the availability of forage biomass is considered to be the primary driver of fluctuations in kangaroo abundance. However, little is known about the population dynamics of the smaller sympatric macropods. We examined the demographic traits of a large colony of yellow‐footed rock‐wallabies (Petrogale xanthopus celeris), following a 2‐year period of above average rainfall. The population was located within a conservation reserve that was subject to a predator control program around its perimeter and on neighbouring properties. The low predator abundance provided an opportunity to gauge the strength of bottom‐up population processes. During the two years of the study, the population declined in size by 53%, resulting from both the virtual absence of juvenile recruitment and the loss of adult wallabies. Although reproductive output was high, low pouch young and juvenile survival rates resulted in few individuals progressing into the adult population. With minimal recruitment, the rate of population decline (r = 0.77) matched the observed adult survival rate (Φ = 0.76). Despite average rainfall conditions during the study, survival rates across all age‐classes were equivalent to those reported for other rock‐wallaby populations during periods of scarcity. The reduced survival rates were attributed to low levels of forage resources, particularly around the wallabies' refuge sites, suggesting the bottom‐up regulation of the colony at high densities. The data suggest that the colony was at temporarily high abundance, following a rainfall driven pulse of recruitment. Conservation management actions for this species should focus on increasing juvenile survival rates within declining populations, through the control of feral goats (Capra hircus), rabbits (Oryctolagus cuniculus) and red foxes (Vulpes vulpes).     

Low dynamics, high longevity and persistence of sessile structural species dwelling on Mediterranean coralligenous outcrops

There is still limited understanding of the processes underlying benthic species dynamics in marine coastal habitats, which are of disproportionate importance in terms of productivity and biodiversity. The life-history traits of long-lived benthic species in these habitats are particularly poorly documented. In this study, we assessed decadal patterns of population dynamics for ten sponge and anthozoan species that play key structural roles in coralligenous outcrops (～25 m depth) in two areas of the NW Mediterranean Sea. This study was based on examination of a unique long-term photographic series, which allowed analysis of population dynamics over extensive spatial and time spans for the very first time. Specifically, 671 individuals were censused annually over periods of 25-, 15-, and 5-years. This long-term study quantitatively revealed a common life-history pattern among the ten studied species, despite the fact they present different growth forms. Low mortality rates (3.4% yr(-1) for all species combined) and infrequent recruitment events (mean value of 3.1±0.5 SE recruits yr(-1)) provided only a very small fraction of the new colonies required to maintain population sizes. Overall, annual mortality and recruitment rates did not differ significantly among years; however, some species displayed important mortality events and recruitment pulses, indicating variability among species. Based on the growth rates of these 10 species, we projected their longevity and, obtained a mean estimated age of 25-200 years. Finally, the low to moderate turnover rates (mean value 0.80% yr(-1)) observed among the coralligenous species were in agreement with their low dynamics and persistence. These results offer solid baseline data and reveal that these habitats are among the most vulnerable to the current increases of anthropogenic disturbances.     

Recruitment and year-to-year variability in a population of Macoma balthica (L.)

Because of methodological problems, macrobenthic studies usually neglect the juvenile stages of invertebrate communities, due to the fact that appearance of recruits in samples is only detected some weeks or even months after their true recruitment. During this period, the temporary meiobenthos undergoes high rates of mortality. From year to year, juvenile survival rate is thus responsible for temporal patterns observed in adult population densities.The results presented here relate to the population dynamics of the tellinid bivalve Macoma balthica (L.). A study of temporary meiobenthos was conducted over two consecutive years in an intertidal Macoma-community located at the mouth of the Gironde Estuary in southwest France. Sampling of juvenile stages required short intervals (2 weeks) between successive samplings and a fine sieving mesh size (63 µm). Other population parameters, such as temporal patterns in density, reproductive cycle, and individual growth, were recorded.Recruitment processes showed a year-to-year variability, with regard to settlement density, settlement period, and survival rate. In 1983, recruitment was moderate and protracted over several months. Only one main recruitment period was detected in 1984, resulting in a high juvenile density. In a previous study (1977), by contrast, recruitment was almost non-existent.This variability is discussed as a function of climatic and sedimentological conditions which prevailed in the estuary throughout the study period. However, none of these physical factors appeared to underlie the recruitment fluctuation in Macoma balthica. It is suggested that biological interactions are of prime importance in regulating population densities in this community.     

Spatial patterns in age- and colony-specific survival in a long-lived seabird across 14 contrasting colonies

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age-dependent survival probabilities across 14 colonies of Herring Gulls Larus argentatus breeding along the Dutch North Sea coast. We used long-term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.     

Climate change causing phase transitions of walleye pollock (Theragra chalcogramma) recruitment dynamics

In 1976 the North Pacific climate shifted, resulting in an average increase of the water temperature. In the Gulf of Alaska the climate shift was followed (i.e. early 1980s) by a gradual but dramatic increase in the abundance of groundfish species that typically prey on pre-recruitment stages of walleye pollock. In the present study we used a previously parameterized model to investigate the effect of these climate and biological changes on the recruitment dynamics of walleye pollock in the Gulf of Alaska. Simulations covered the 1970-2000 time frame and emphasized the medium-to-long temporal scale (i.e. about 5-10 years) of environmental variability. Results showed that during periods characterized by high sea surface temperature and high predation on juvenile pollock stages, recruitment variability and magnitude were below average, and recruitment control was delayed to stages older than the 0-group. Opposite dynamics (i.e. high abundance and variability, and early recruitment control) occurred during periods characterized by low temperature and predation. These results are in general agreement with empirical observations, and allowed us to formulate causal explanations for their occurrence. We interpreted the delay of recruitment control and the reduction of variability as an effect of increased constraint on the abundance of post age-0 stages, in turn imposed by high density dependence and predation mortality. On the other hand, low density-dependence and predation favoured post age-0 survival, and allowed for an unconstrained link between larval and recruitment abundance. Our findings demonstrate that the dominant mechanisms of pollock survival change over contrasting climate regimes. Such changes may in turn cause a phase transition of recruitment dynamics with profound implications for the management of the entire stock.     

Recruitment and mortality of the temperate coral Cladocora caespitosa: implications for the recovery of endangered populations

Long-lived species are characterized by low recruitment and mortality. In these species, longevity buffers low recruitment, but when catastrophic disturbances alter mortality, recruitment becomes critical for population recovery. In this study, we assessed basic biological traits—recruitment, post-settlement growth, and the mortality of juvenile corals—and related these factors to the adult mortality of one of the most important populations of the Mediterranean reef-building coral Cladocora caespitosa over a period of 6 yr. Adult mortality and recruitment rates were low (~1 % and 0.30 recruits m^?2 yr^?1, respectively), whereas the juvenile colony mortality was comparatively high (29 % in the smallest size-class, <5 polyps). The low recruitment rates will hardly balance the recurrent climate-related mortality that has affected this population. Conservation plans and inclusion in the protection lists are urgently needed, given the escalating threats and slow dynamics of this species.     

Distinguishing effects of juvenile mortality and dispersal on recruitment

Detailed data on juvenile survival are rare in the literature. Although many studies estimate recruitment, if you cannot distinguish between permanent dispersal and mortality, the management implications for a population may be unclear. We estimated juvenile survival in a reintroduced North Island robin (Petroica longipes) population in a protected sanctuary surrounded by an unprotected landscape where the species is extirpated. The population has had marginal population growth due to poor recruitment so we modeled 3 types of data (resighting of fledglings, radio-telemetry of independent juveniles, resighting of adults) in an integrated framework to determine the life stages where high mortality was occurring, and to distinguish mortality from dispersal. Approximately 16% of birds that fledged (n = 109) were present at the start of the next breeding season, consistent with recruitment rates from previous years. Low survival in the first 6 weeks after fledging was the primary cause of poor recruitment. Only 50% survived to independence (4 weeks after fledging), and 18% survived to the end of the radio-tracking period (14 weeks), after which juvenile survival matched adult survival. No dispersal from the sanctuary occurred during the radio-tracking period. Juveniles moved between adjacent forest fragments within the sanctuary, but did not leave the sanctuary. This information, which demonstrates the importance of distinguishing between natal mortality and dispersal, is important for ongoing management of the site and selection of future reintroduction sites for this species. © 2019 The Wildlife Society.     

Effects of regional climate and small‐scale habitat quality on performance in the relict species Ramonda myconi

Abstract. The Mediterranean Basin harbours paleo‐endemic species with a highly restricted and fragmented distribution. Many of them might also be of the remnant type, for which the regional dynamics depends on the persistence of extant populations. Therefore, a key issue for the long‐term persistence of these species is to assess the variability and effects of ecological factors determining plant performance. We investigated the spatio‐temporal variability in plant traits and ecological factors of Ramonda myconi, a preglacial relict species with remnant dynamics, in 5 populations over 4–7 yr. Ecological factors contributing to fecundity showed a high degree of between‐year variability. Pre‐dispersal fruit predation had a minor influence on total reproductive output, and most of the variability was found among individuals within populations and years. Spatio‐temporal variability in growth and survival was rather low but significant, whereas recruitment showed important between‐population variability. Among‐year variability in fecundity and growth was related to climatic fluctuations on a regional scale, notably rainfall and temperature in a particular period, while the spatial variability in survival and recruitment was explained by within‐population (patch) habitat quality. Although R. myconi is able to withstand repeated periods of drought, water availability seems to be the most important factor affecting plant performance in all the study populations. These findings suggest that the long‐term persistence of species showing remnant population dynamics in habitats under the influence of Mediterranean climate might be threatened by increased aridity as a result of climate change.