Studies on Cepaea III. Ecogenetics of a population of Cepaea nemoralis (L.) subject to strong area effects

1968 ◽  
Vol 253 (789) ◽  
pp. 447-482 ◽  
Keyword(s):  
Survival Rates ◽  
Adult Survival ◽  
Frequency Variation ◽  
Snail Population ◽  
Differential Survival ◽  
Active Season ◽  
Cepaea Nemoralis ◽  
Area Effects ◽  
Colour Morphs ◽  
Morph Frequency

On the discovery of area effects in morph frequency variation in the snail Cepaea nemoralis on the Marlborough Downs (Cain & Currey 1963 a) an intensive study with mark-release-recapture methods of a population subject to these effects was begun. The area investigated was divided into four quarters (downland grass) and two nettlepatches; the snail population is continuous through the area. Frequent visits were made during the snails’ active season in 1962, 1963 and 1964; in 1965 and 1966 a single large sample was collected, marked and released in the spring. Five-banded shells are absent. The scoring of mid-bandeds with reduced bands being difficult, attention was concentrated on the principal colour morphs, yellow, pink and brown. Thrushes were predating the snails heavily in 1962, but the hard winter of 1962/3 removed them, and they have not yet returned in any numbers; the snail population does not seem to have been affected by this hard season. Throughout the period of investigation, the density of snails in the nettlepatches has been about ten times that in quarters 2, 3 and 4. Quarter 1 has less than half the density in the other quarters, and differs markedly from them and the nettlepatches in morph frequency, although it resembles quarter 2 strongly in vegetation. It is likely, therefore, that the snails are extremely localized in their wanderings, the more so as we had to collect from each division, take the samples away to be marked, and scatter them on release, each at random in its own division. Our estimates of migration from one division to another also suggest strong localization and perhaps homing. The total population in the area is about 3000 adults. Subpopulations have decreased in all divisions from 1963 to 1965. Adult survival rates are high, about 0.65 per year; no differential survival of the colour classes has been found, but much more data are needed. Predation by thrushes in 1962 was heavy in the summer, but not in proportion to snail density; the nettlepatches were proportionately much less predated, probably because of their dense growth of herbage. Winter predation, by contrast, was almost entirely in the nettlepatches, then showing expanses of bare earth. A check on our own efficiency of collecting shows that we are taking non-random samples in the quarters (downland grass) but not in the nettlepatches. We find pinks rather more conspicuous than yellows, but dark browns much less conspicuous than either. As the snails’ bodies in this area are very dark, yellows appear green, pinks dirty straw-colour. It seems unlikely that browns are really more cryptic visually than yellows. Possibly their behaviour is different. The samples of predated shells taken by the thrushes agree very closely with our samples, and it appears that they also are predating with a bias (missing browns) in the quarters but not in the nettlepatches. Morph frequencies show no sign of alteration in the period of investigation, except that in 1963 and 1964 there was a drop in percentages of browns in quarters 2, 3 and 4, apparently not continuing in 1965 and 1966. (The compensatory increase is shared equally between pinks and yellows.) This could well be due to the sudden cessation of selection by thrushes, but the rate seems excessive if there was selection only on adults. There is no obvious relation between morph frequencies and population density. The growth in size of the juveniles in our samples has been studied through the snails’ active season. It is clear that they take two years to reach maturity (i.e. to form the lip terminating the adult shell). This finding and the survival rates give a minimum generation interval of four years, and the actual period may be close to five in this area.

Studies on Cepaea II. Area effects and visual selection in Cepaea nemoralis (L.) and Cepaea hortensis

1968 ◽  
Vol 253 (789) ◽  
pp. 397-446 ◽  
Keyword(s):  
High Frequency ◽  
Regional Differences ◽  
Good Evidence ◽  
Visual Selection ◽  
Frequency Variation ◽  
Cepaea Nemoralis ◽  
Area Effects ◽  
Habitat Variation ◽  
The Second Variation ◽  
Morph Frequency

The snails Cepaea nemoralis and C. hortensis show an extensive and stable polymorphism involving the colour and banding pattern of the shell. The surveys on the Berkshire Downs, the Purbeck Hills and part of lowland Somerset reported here show, together with previous ones, that both species can occur in lowland and chalk upland localities, but the distribution of the two species in any one locality is different. This difference may be related to topography as on the Berkshire Downs and the Purbecks, or to habitat as in south-east Somerset. There are no regional differences in the C. nemoralis polymorphism, most morphs so far recognized being present in every locality. The colour polymorphism in C. hortensis is much more extensive in the southern localities than in those from central England and there are alo regional differences in the banding polymorphism. Two types of morph frequency variation occur in both species. The first described was variation with habitat, the second, variation related to geographical position. The surveys show that habitat variation occurs in both lowland and upland areas, although it does not necessarily occur in either. Thus both species show morph frequency variation with habitat round Oxford and on the eastern Berkshire Downs. Only C. hortensis shows such variation on the Purbeck Hills although C. nemoralis is present there. The evidence, although not conclusive, indicates that neither species shows habitat variation in lowland south-east Somerset, but there is good evidence that neither species shows such variation on the western Berkshire Downs, the Marlborough Downs or Salisbury Plain. The morphs showing frequency variation with habitat are not always the same in either species. Round Oxford, and on the eastern Berkshire Downs, brown, pink and banded C. nemoralis with at least the upper two bands missing, are at a high frequency in woods, and yellows and bandeds are at a high frequency in other habitats. C. hortensis , on the other hand, shows variation in the frequency of fused bands and yellow effectively unbandeds between habitats in these two localities. On the central Berkshire Downs, spread banded show habitat variation together with other morphs in C. nemoralis . On the Purbeck Hills where pinks, browns and unbandeds are common in C. hortensis the habitat variation is very similar to that of C. nemoralis round Oxford. Habitat variation is not restricted to strikingly different morphs. Different types of pink C. nemoralis show such variation on the Berkshire Downs, and fusions of the upper or more bands in C. hortensis also show variation there. All the variation of morph frequency described above is best explained on the hypothesis of visual selection. Morph frequency variations related to geography give rise to large areas of stable morph frequency irrespective of habitat, the so-called area effects. The surveys to date indicate that area effects are restricted in both species to upland localities. The Berkshire Downs survey of C. nemoralis shows that area effects and habitat variation are not mutually exclusive. In different localities, related on an east/west axis, most morphs may show habitat variation, some show habitat variation and some area effects, or most show area effects. Area effects may occur in both species in the same locality as on the western Berkshire Downs, where the limits of the various area effects in the two species are semi-coincidental, or they may only occur in one species, C. nemoralis , on the Purbeck Hills. There is no experimental evidence as to the cause of area effects but there is some evidence from the present surveys which supports Cain & Currey’s (1963 a, c ) suggestion that they are maintained by selection.

scholarly journals Predation and survival in reintroduced populations of the Common hamster Cricetus cricetus in the Netherlands

2020 ◽  
Vol 100 (6) ◽  
pp. 569-579
Author(s):  
Maurice J. J. La Haye ◽  
Ruud J. M. van Kats ◽  
Gerard J. D. M. Müskens ◽  
Caspar A. Hallmann ◽  
Eelke Jongejans
Keyword(s):  
The Netherlands ◽  
Survival Rates ◽  
Agricultural Practices ◽  
Adult Survival ◽  
Cricetus Cricetus ◽  
Active Season ◽  
Common Hamster ◽  
Viable Population ◽  
Survival And Reproduction ◽  
Small Mustelids

AbstractEuropean populations of Common hamster (Cricetus cricetus) have dramatically declined in the last decades, and in many EU countries, the species is on the brink of extinction. In the Netherlands, a research and reintroduction program was started in three areas with hamster-friendly management to reverse the decline of the species. Since 2002, more than 800 captive-bred and wild-born hamsters were monitored using implant radiotransmitters to quantify survival rates and discover the main causes of death after release compared to those of wild individuals. Individuals with a transmitter were regularly checked at their burrow. Predation by foxes, birds of prey, and small mustelids was the most important cause of mortality of this medium-sized rodent, while crop type and harvest regime were also likely to be important drivers as they influenced survival rates through the presence or absence of protective cover. The fitted weekly survival model showed that male hamsters had much lower survival rates during the active season than females, which corresponds with the ‘risky male hypothesis’. Survival rates of females appeared too low to keep populations at a stable level. To establish a viable population, more optimal environmental conditions for both survival and reproduction of the hamsters are necessary. Using electric fences around fields with hamsters significantly increased the survival of females. However, hamster conservationists need to consider not just subadult and adult survival rates, but also habitat connectivity, weather effects on reproduction, and alternative agricultural practices on a landscape scale.

Persistence of giants: population dynamics of the limpet Scutellastra laticostata on rocky shores in Western Australia

2020 ◽  
Vol 646 ◽  
pp. 79-92
Author(s):  
RE Scheibling ◽  
R Black
Keyword(s):  
Population Dynamics ◽  
Western Australia ◽  
Size Structure ◽  
Survival Rates ◽  
Maximum Size ◽  
High Rate ◽  
Adult Survival ◽  
Rocky Shores ◽  
Adult Size ◽  
Decadal Time Scale

Population dynamics and life history traits of the ‘giant’ limpet Scutellastra laticostata on intertidal limestone platforms at Rottnest Island, Western Australia, were recorded by interannual (January/February) monitoring of limpet density and size structure, and relocation of marked individuals, at 3 locations over periods of 13-16 yr between 1993 and 2020. Limpet densities ranged from 4 to 9 ind. m-2 on wave-swept seaward margins of platforms at 2 locations and on a rocky notch at the landward margin of the platform at a third. Juvenile recruits (25-55 mm shell length) were present each year, usually at low densities (<1 m-2), but localized pulses of recruitment occurred in some years. Annual survival rates of marked limpets varied among sites and cohorts, ranging from 0.42 yr-1 at the notch to 0.79 and 0.87 yr-1 on the platforms. A mass mortality of limpets on the platforms occurred in 2003, likely mediated by thermal stress during daytime low tides, coincident with high air temperatures and calm seas. Juveniles grew rapidly to adult size within 2 yr. Asymptotic size (L∞, von Bertalanffy growth model) ranged from 89 to 97 mm, and maximum size from 100 to 113 mm, on platforms. Growth rate and maximum size were lower on the notch. Our empirical observations and simulation models suggest that these populations are relatively stable on a decadal time scale. The frequency and magnitude of recruitment pulses and high rate of adult survival provide considerable inertia, enabling persistence of these populations in the face of sporadic climatic extremes.

scholarly journals Warming Arctic summers unlikely to increase productivity of shorebirds through renesting

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sarah T. Saalfeld ◽  
Brooke L. Hill ◽  
Christine M. Hunter ◽  
Charles J. Frost ◽  
Richard B. Lanctot
Keyword(s):  
Climate Change ◽  
Survival Rates ◽  
The Arctic ◽  
Adult Survival ◽  
Chick Survival ◽  
Ecological Processes ◽  
Bird Populations ◽  
Phenological Mismatch ◽  
Daily Survival ◽  
Adequate Food

AbstractClimate change in the Arctic is leading to earlier summers, creating a phenological mismatch between the hatching of insectivorous birds and the availability of their invertebrate prey. While phenological mismatch would presumably lower the survival of chicks, climate change is also leading to longer, warmer summers that may increase the annual productivity of birds by allowing adults to lay nests over a longer period of time, replace more nests that fail, and provide physiological relief to chicks (i.e., warmer temperatures that reduce thermoregulatory costs). However, there is little information on how these competing ecological processes will ultimately impact the demography of bird populations. In 2008 and 2009, we investigated the survival of chicks from initial and experimentally-induced replacement nests of arcticola Dunlin (Calidris alpina) breeding near Utqiaġvik, Alaska. We monitored survival of 66 broods from 41 initial and 25 replacement nests. Based on the average hatch date of each group, chick survival (up to age 15 days) from replacement nests (Ŝi = 0.10; 95% CI = 0.02–0.22) was substantially lower than initial nests (Ŝi = 0.67; 95% CI = 0.48–0.81). Daily survival rates were greater for older chicks, chicks from earlier-laid clutches, and during periods of greater invertebrate availability. As temperature was less important to daily survival rates of shorebird chicks than invertebrate availability, our results indicate that any physiological relief experienced by chicks will likely be overshadowed by the need for adequate food. Furthermore, the processes creating a phenological mismatch between hatching of shorebird young and invertebrate emergence ensures that warmer, longer breeding seasons will not translate into abundant food throughout the longer summers. Thus, despite having a greater opportunity to nest later (and potentially replace nests), young from these late-hatching broods will likely not have sufficient food to survive. Collectively, these results indicate that warmer, longer summers in the Arctic are unlikely to increase annual recruitment rates, and thus unable to compensate for low adult survival, which is typically limited by factors away from the Arctic-breeding grounds.

scholarly journals Fitness of breeders in social Damaraland mole-rats is independent of group size

2021 ◽  
Author(s):  
Jack Thorley ◽  
Hanna Bensch ◽  
Kyle Finn ◽  
Tim Clutton-Brock ◽  
Markus Zöttl
Keyword(s):  
Reproductive Success ◽  
Group Size ◽  
Survival Rates ◽  
Group Living ◽  
Adult Survival ◽  
High Survival ◽  
Successful Reproduction ◽  
Related Group ◽  
Group Members ◽  
Using Data

Damaraland mole-rats (Fukomys damarensis) are usually viewed as an obligatorily group living eusocial species in which successful reproduction is dependent on reproductive altruism of closely related group members. However, the reproductive ecology of social mole-rats in their natural environment remains poorly understood and it is unclear to what extent successful reproduction is dependent on assistance from other group members. Using data from a 7-year field study of marked individuals, we show that, after dispersal from their natal group, individuals typically settled alone in new burrow systems where they enjoyed high survival rates, and often remained in good body condition for several years before finding a mate. Unlike most other eusocial or singular cooperative breeders, we found that Damaraland mole-rats reproduced successfully in pairs without helpers and experimentally formed pairs had the same reproductive success as larger established groups. Overall there was only a weak increase in reproductive success with increasing group size and no effect of group size on adult survival rates across the population. Juveniles in large groups grew faster early in life but their growth rates declined subsequently so that they eventually plateaued at a lower maximum body mass than juveniles from small groups. Taken together, our data suggest that the fitness benefits of group living to breeders are small and we suggest that extended philopatry in Damaraland mole-rats has evolved because of the high costs and constraints of dispersal rather than because of strong indirect benefits accrued through cooperative behaviour.

scholarly journals Preliminary survival and movement data for a declining population of Flesh-footed Shearwater Ardenna carneipes in Western Australia provides insights into marine threats

2018 ◽  
Vol 29 (2) ◽  
pp. 327-337 ◽  
Author(s):  
JENNIFER L. LAVERS ◽  
SIMEON LISOVSKI ◽  
ALEXANDER L. BOND
Keyword(s):  
Western Australia ◽  
Survival Rates ◽  
Adult Survival ◽  
Seabird Species ◽  
Movement Data ◽  
Central Indian Ocean ◽  
Breeding Grounds ◽  
Wintering Areas ◽  
Fisheries Bycatch ◽  
Western Australian

SummarySeabirds face diverse threats on their breeding islands and while at sea. Human activities have been linked to the decline of seabird populations, yet over-wintering areas typically receive little or no protection. Adult survival rates, a crucial parameter for population persistence in long-lived species, tend to be spatially or temporally restricted for many seabird species, limiting our understanding of factors driving population trends at some sites. We used bio-loggers to study the migration of Western Australian Flesh-footed Shearwaters Ardenna carneipes carneipes and estimated adult survival over five years. Western Australia is home to around 35% of the world’s breeding Flesh-footed Shearwaters, a population which was up-listed to Vulnerable in 2015. During the austral winter, shearwaters migrated across the central Indian Ocean to their non-breeding grounds off western Sri Lanka. Low site fidelity on breeding islands, mortality of adult birds at sea (e.g. fisheries bycatch), and low annual breeding frequency likely contributed to the low estimated annual adult survival (2011–2015: ϕ = 0.634-0.835).

Impacts of recolonizing gray wolves (Canis lupus) on survival and mortality in two sympatric ungulates

2018 ◽  
Vol 96 (7) ◽  
pp. 760-768 ◽  
Author(s):  
J.A. Dellinger ◽  
C.R. Shores ◽  
M. Marsh ◽  
M.R. Heithaus ◽  
W.J. Ripple ◽  
...  
Keyword(s):  
Canis Lupus ◽  
Mule Deer ◽  
Survival Rates ◽  
Odocoileus Hemionus ◽  
Mortality Rates ◽  
Adult Survival ◽  
Mortality Data ◽  
Gray Wolf ◽  
Gray Wolves ◽  
Large Predators

There is growing recognition that humans may mediate the strength and nature of the ecological effects of large predators. We took advantage of ongoing gray wolf (Canis lupus Linnaeus, 1758) recolonization in Washington, USA, to contrast adult survival rates and sources of mortality for mule deer (Odocoileus hemionus (Rafinesque, 1817)) and white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) in areas with and without wolf packs in a managed landscape dominated by multiple human uses. We tested the hypothesis that the addition of wolves to the existing predator guild would augment predator-induced mortality rates for both ungulates. Source of mortality data from adult mule deer and white-tailed deer, respectively, revealed that wolf-related mortality was low compared with that inflicted by other predators or humans. Predator-caused mortality was largely confined to winter. There was little effect of wolf presence on adult deer mortality rates, and there was no difference in mortality between the two deer species relative to wolf-free or wolf-occupied sites. Although this study occurred early in wolf recovery in Washington, our results differ from those demonstrated for gray wolves in protected areas. Thus, we encourage further investigation of effects of direct predation by recolonizing large carnivores on prey in human-dominated landscapes.

Variation in floral morph ratios in tristylous Oxalis squamata (Oxalidaceae): an Andean alpine endemic

Botany ◽  
2012 ◽  
Vol 90 (11) ◽  
pp. 1180-1185 ◽  
Author(s):  
Spencer C.H. Barrett ◽  
Mary T.K. Arroyo
Keyword(s):  
Clonal Propagation ◽  
Frequency Variation ◽  
Significant Heterogeneity ◽  
Approach To Equilibrium ◽  
Central Chile ◽  
Large Populations ◽  
Negative Frequency Dependent Selection ◽  
Morph Ratios ◽  
Floral Morph ◽  
Morph Frequency

Negative frequency-dependent selection resulting from disassortative mating should result in equal morph ratios in tristylous populations at equilibrium. However, surveys of morph-frequency variation in tristylous species commonly report deviations from equality. Here, we report variation in morph ratios in Oxalis squamata Zucc., an endemic of the Andean region of Chile and Argentina. Absence of clonal propagation in this species allows unambiguous estimates of the morph ratio of genets. We sampled floral morph ratios in 20 populations occurring in Central Chile and investigated the relation between morph evenness in populations and their size. All populations of O. squamata were tristylous but with significant heterogeneity among populations in morph ratios. Although small populations exhibited a greater variance in morph evenness, biased ratios were also evident in several large populations. We found no evidence of morph loss or a consistent bias in morph frequencies as reported in some tristylous species. Biased morph frequencies in large populations probably arise from episodic sexual recruitment following disturbance and a slow approach to equilibrium.

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