Relative abundance of culled and not culled American mink populations in northeast Spain and their potential distribution: are culling campaigns effective?

The effectiveness of culling campaigns to eradicate or limit populations of the alien, invasive American mink in Catalonia was studied by comparing the annual relative abundance of culled versus non-culled populations. We selected three populations that were culled under government campaigns and a fourth that served as a control and hence was left undisturbed (not culled). The study took place between 2002 and 2006 and annual relative abundances were estimated from trapping with bankside traps. The abundance of all four populations remained relatively stable throughout the study period. However, the annual relative abundance of the culled populations was lower than that of the non-culled population, which indicates that culling may have lowered the densities of mink, although eradication was not achieved. We also determined the potential distribution of the American mink in Catalonia by means of a habitat suitability model. The final aim was to assist in planning this species’ management. Almost all watercourses in Catalonia were identified as suitable for the American mink, with preferred areas located in the northeast. We recommend that the government and administrations promote culling campaigns focused on limiting the spread of the American mink as eradication is likely to be difficult to be achieved under the current situation. Target areas should be located on the edges of the American mink’s range and should be prioritized to limit the spread of this species to areas in which there are endangered native species.     

Effects of size, culling and social history on growth of cultured elvers, Anguilla anguilla (L.)

The growth of newly-caught elvers was measured after they were separated into four size categories and induced to feed. All sizes grew equally well, indicating that size differences at capture reflected migration history rather than the presence of genetically poor or good growers. Socially experienced groups of elvers of equivalent size grew, on average, less well due to the presence of socially suppressed fish and fish that did not respond so well to handling or a new social environment.
Replicate groups of rapidly-growing elvers were culled at either 2- or 4-weekly intervals. The large animals removed were replaced by animals of modal size and the growth of selected residual size groups was compared to unculled control groups. Culling tended to increase the instantaneous growth coefficient of remaining small elvers but the added elvers of modal size may have exerted a disproportionate influence on mean growth rates.
The effect of large elvers on the growth of small elvers (and vice versa) was monitored using fish labelled subcutaneously with acrylic paint. Separate populations of elvers of each size group were used as controls. After 82 days in mixed populations, about 36% of the original large fish had been' overtaken' by small category fish.
The results suggested that, following disturbance, the expression of growth in elvers was not necessarily related to size or previous hierarchical position but may be governed by behavioural or physiological responses to handling and changed social environments.     

Does selection on horn length of males and females differ in protected and hunted populations of a weakly dimorphic ungulate?

Weaponry in ungulates may be costly to grow and maintain, and different selective pressures in males and females may lead to sex‐biased natural survival. Sexual differences in the relationship between weapon growth and survival may increase under anthropogenic selection through culling, for example because of trophy hunting. Selection on weaponry growth under different scenarios has been largely investigated in males of highly dimorphic ungulates, for which survival costs (either natural or hunting related) are thought to be greatest. Little is known, however, about the survival costs of weaponry in males and females of weakly dimorphic species. We collected information on horn length and age at death/shooting of 407 chamois Rupicapra rupicapra in a protected population and in two hunted populations with different hunting regimes, to explore sexual differences in the selection on early horn growth under contrasting selective pressures. We also investigated the variation of horn growth and body mass in yearling males (n = 688) and females (n = 539) culled in one of the hunted populations over 14 years. The relationship between horn growth and survival showed remarkable sexual differences under different evolutionary scenarios. Within the protected population, under natural selection, we found no significant trade‐off in either males or females. Under anthropogenic pressure, selection on early horn growth of culled individuals showed diametrically opposed sex‐biased patterns, depending on the culling regime and hunters’ preferences. Despite the selective bias between males and females in one of the hunted populations, we did not detect significant sex‐specific differences in the long‐term pattern of early growth. The relationship between early horn growth and natural survival in either sex might suggest stabilizing selection on horn size in chamois. Selection through culling can be strongly sex‐biased also in weakly dimorphic species, depending on hunters’ preferences and hunting regulations, and long‐term data are needed to reveal potential undesirable evolutionary consequences.     

Density-dependent colonization and natural disturbance limit the effectiveness of invasive lionfish culling efforts

Culling can be an effective management tool for reducing populations of invasive species to levels that minimize ecological effects. However, culling is labour-intensive, costly, and may have unintended ecological consequences. In the Caribbean, culling is widely used to control invasive Indo-Pacific lionfish, Pterois volitans and P. miles, but the effectiveness of infrequent culling in terms of reducing lionfish abundance and halting native prey decline is unclear. In a 21-month-long field experiment on natural reefs, we found that culling effectiveness changed after the passage of a hurricane part-way through the experiment. Before the hurricane, infrequent culling resulted in substantial reductions in lionfish density (60–79%, on average, albeit with large uncertainty) and slight increases in native prey species richness, but was insufficient to stem the decline in native prey biomass. Culling every 3 months (i.e., quarterly) and every 6 months (i.e., biannually) had similar effects on lionfish density and native prey fishes because of high rates of lionfish colonization among reefs. After the hurricane, lionfish densities were greater on all culled reefs compared to non-culled reefs, and prey biomass declined by 92%, and species richness by 71%, on biannually culled reefs. The two culling frequencies we examined therefore seem to offer a poor trade-off between the demonstrated conservation gains that can be achieved with frequent culling and the economy of time and money realized by infrequent culling. Moreover, stochastic events such as hurricanes can drastically limit the effectiveness of culling efforts.     

The Duration of the Effects of Repeated Widespread Badger Culling on Cattle Tuberculosis Following the Cessation of Culling

Background

In the British Isles, control of cattle tuberculosis (TB) is hindered by persistent infection of wild badger (Meles meles) populations. A large-scale field trial—the Randomised Badger Culling Trial (RBCT)—previously showed that widespread badger culling produced modest reductions in cattle TB incidence during culling, which were offset by elevated TB risks for cattle on adjoining lands. Once culling was halted, beneficial effects inside culling areas increased, while detrimental effects on adjoining lands disappeared. However, a full assessment of the utility of badger culling requires information on the duration of culling effects.

Methodology/Principal Findings

We monitored cattle TB incidence in and around RBCT areas after culling ended. We found that benefits inside culled areas declined over time, and were no longer detectable by three years post-culling. On adjoining lands, a trend suggesting beneficial effects immediately after the end of culling was insignificant, and disappeared after 18 months post-culling. From completion of the first cull to the loss of detectable effects (an average five-year culling period plus 2.5 years post-culling), cattle TB incidence was 28.7% lower (95% confidence interval [CI] 20.7 to 35.8% lower) inside ten 100 km² culled areas than inside ten matched no-culling areas, and comparable (11.7% higher, 95% CI: 13.0% lower to 43.4% higher, p  =  0.39) on lands ≤2 km outside culled and no-culling areas. The financial costs of culling an idealized 150 km² area would exceed the savings achieved through reduced cattle TB, by factors of 2 to 3.5.

Conclusions/Significance

Our findings show that the reductions in cattle TB incidence achieved by repeated badger culling were not sustained in the long term after culling ended and did not offset the financial costs of culling. These results, combined with evaluation of alternative culling methods, suggest that badger culling is unlikely to contribute effectively to the control of cattle TB in Britain.     

Culling-induced social perturbation in Eurasian badgers Meles meles and the management of TB in cattle: an analysis of a critical problem in applied ecology

The Eurasian badger (Meles meles) is implicated in the transmission of bovine tuberculosis (TB) to cattle in the UK and Republic of Ireland. Badger culling has been employed for the control of TB in cattle in both countries, with varying results. Social perturbation of badger populations following culling has been proposed as an explanation for the failure of culling to consistently demonstrate significant reductions in cattle TB. Field studies indicate that culling badgers may result in increased immigration into culled areas, disruption of territoriality, increased ranging and mixing between social groups. Our analysis shows that some measures of sociality may remain significantly disrupted for up to 8 years after culling. This may have epidemiological consequences because previous research has shown that even in a relatively undisturbed badger population, movements between groups are associated with increases in the incidence of Mycobacterium bovis infection. This is consistent with the results from a large-scale field trial, which demonstrated decreased benefits of culling at the edges of culled areas, and an increase in herd breakdown rates in neighbouring cattle.     

Marine mammal culling programs: review of effects on predator and prey populations

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Associations between the breeding values of Holstein-Friesian bulls and longevity and culling reasons of their daughters

Taking into account functional traits in the breeding practice should lead to a longer productive life of cows. However, despite the increased contribution of these traits in bull selection indices, their daughters are frequently culled as early as the 2nd or 3rd lactation. The problem is whether and to what extent the genetic potential of animals is realized in the production practice. Therefore, the purpose of this study was to determine the associations between the breeding value (BV) of bulls and their daughters for cow longevity and culling reasons in the Holstein-Friesian cattle population in Poland. Data for 532 062 cows culled in 2012, 2015, and 2018 were analyzed. A majority of 5 045 cow sires originated from Poland, Germany, France, the Netherlands, and the United States. The highest variation in the contribution of culling reasons was for the cows culled at the age of 2–4 years. The contribution of the culling reasons, analyzed in relation to the cow culling age, remained similar and the only exception was culling because of old age, for which a significant increase was observed only for the culling age of at least 9 years (13.8%), which was reached by only 7.3% of the cows. The sires were characterized by generally high BV for conformation and reproductive traits. However, they had, at most, the average genetic potential for functional longevity. There were a number of beneficial associations found between the BV of bulls and the distribution of culling reasons in their daughters. For example, it concerns relations between the somatic cell score in milk and culling due to udder diseases and low milk yield, between the interval from calving to first insemination and low milk yield, between the protein yield and old age, or between the BV for certain conformation traits (size, udder) and cow culling due to age. In these cases, as the BV increased for a given trait, the contribution of the corresponding cow culling reason tended to decrease. Our study showed that it seems reasonable to consider Holstein-Friesian cows aged at least 9 years at culling to be long-living animals. This is primarily evidenced by the rapid increase in the culling due to old age in relation to younger cows. Nowadays the above age limit can be suggested as a criterion of longevity for Holstein-Friesian cows but the criterion should be updated to the relation genotype-environment-economy that tends to change over time.     

Restricted movement by mottled sculpin (pisces: cottidae) in a southern Appalachian stream

1. We used direct observation and mark‐recapture techniques to quantify movements by mottled sculpins (Cottus bairdi) in a 1 km segment of Shope Fork in western North Carolina. Our objectives were to: (i) quantify the overall rate of sculpin movement, (ii) assess variation in movement among years, individuals, and sculpin size classes, (iii) relate movement to variation in stream flow and population size structure, and (iv) quantify relationships between movement and individual growth rates. 2. Movements were very restricted: median and mean movement distances for all sculpin size classes over a 45 day period were 1.3 and 4.4 m respectively. Nevertheless, there was a high degree of intrapopulation and temporal variation in sculpin movement. Movement of juveniles increased with discharge and with the density of large adults. Movement by small and large adults was not influenced by stream flow, but large adults where more mobile when their own density was high. Finally, there were differences in the growth rates of mobile and sedentary sculpins. Mobile juveniles grew faster than sedentary individuals under conditions of low flow and high density of large adults, whereas adults exhibited the opposite pattern. 3. Our results support the hypothesis that juvenile movement and growth is influenced by both intraspecific interactions with adults and stream flow. In contrast, adult movement appears to be influenced by competitive interactions among residents for suitable space. The relationship between movement and growth may provide a negative feedback mechanism regulating mottled sculpin populations in this system.     

Understanding basic species population dynamics for effective control: a case study on community-led culling of the common myna (Acridotheres tristis)

Population manipulation of introduced species can be difficult and many widespread eradication or reduction attempts have failed. Understanding the population dynamics of a species is essential for undertaking a successful control program. Despite this, control attempts are frequently undertaken with limited knowledge of the species population dynamics. For example, in Australia, concern over the impact of the introduced common myna (Acridotheres tristis) has led to community members culling the species. In this paper, we assessed the impact of community-led common myna culling program over broad and fine-scales in Canberra, Australia. We utilized a basic population model to enhance understanding of common myna population dynamics and the potential influence of various culling regimes. We found a significant negative relationship between common myna abundance and culling at fine-scales (1 km²). However, over broad-scales the relationship between common myna abundance and culling was not significant. Our population model indicated culling at a rate of 25 birds per km² per year would reduce common myna abundance, regardless of initial density. Our results suggest that currently too few individuals are being removed from the Canberra population, and natural reproduction, survival and/or immigration is able to replace the culled individuals. This highlights the value of undertaking basic population modeling to assess if potential control measures are capable of achieving desired outcomes. Our work provides information for researchers, government and community groups interested in controlling not only the common myna, but also other introduced species.     

Spatial Targeting for Bovine Tuberculosis Control: Can the Locations of Infected Cattle Be Used to Find Infected Badgers?

Bovine tuberculosis is a disease of historical importance to human health in the UK that remains a major animal health and economic issue. Control of the disease in cattle is complicated by the presence of a reservoir species, the Eurasian badger. In spite of uncertainty in the degree to which cattle disease results from transmission from badgers, and opposition from environmental groups, culling of badgers has been licenced in two large areas in England. Methods to limit culls to smaller areas that target badgers infected with TB whilst minimising the number of uninfected badgers culled is therefore of considerable interest. Here, we use historical data from a large-scale field trial of badger culling to assess two alternative hypothetical methods of targeting TB-infected badgers based on the distribution of cattle TB incidents: (i) a simple circular ‘ring cull’; and (ii) geographic profiling, a novel technique for spatial targeting of infectious disease control that predicts the locations of sources of infection based on the distribution of linked cases. Our results showed that both methods required coverage of very large areas to ensure a substantial proportion of infected badgers were removed, and would result in many uninfected badgers being culled. Geographic profiling, which accounts for clustering of infections in badger and cattle populations, produced a small but non-significant increase in the proportion of setts with TB-infected compared to uninfected badgers included in a cull. It also provided no overall improvement at targeting setts with infected badgers compared to the ring cull. Cattle TB incidents in this study were therefore insufficiently clustered around TB-infected badger setts to design an efficient spatially targeted cull; and this analysis provided no evidence to support a move towards spatially targeted badger culling policies for bovine TB control.     

The effects of different dissolved oxygen regimes on the growth of a freshwater leech

The growth rates of two size classes of Nephelopsis obscura , a freshwater predatory leech, were determined at five different dissolved oxygen regimes (three constant 10%, 100%, 300%. and two diel cyclical 10-100% and 100-300%) at 15°C Both small and large N obscura showed highest growth rates in the diel 100-300% regime and the lowest in the constant 10% or diel 10-100% regimes These differences in growth rate affect the predicted time to reach the minimum size for reproduction, e g 42 8 d m constant 10% and 315dm diel 100-300% regimes for small and 67 9 d and 8 8 d respectively for large N obscura These differences determine whether individuals surviving winter reach maturity and produce cocoons in the spring or the autumn and whether individuals hatched in the spring can reach mature size the same summer     

Genetic evidence that culling increases badger movement: implications for the spread of bovine tuberculosis

The Eurasian badger (Meles meles) has been implicated in the transmission of bovine tuberculosis (TB, caused by Mycobacterium bovis) to cattle. However, evidence suggests that attempts to reduce the spread of TB among cattle in Britain by culling badgers have mixed effects. A large-scale field experiment (the randomized badger culling trial, RBCT) showed that widespread proactive badger culling reduced the incidence of TB in cattle within culled areas but that TB incidence increased in adjoining areas. Additionally, localized reactive badger culling increased the incidence of TB in cattle. It has been suggested that culling-induced perturbation of badger social structure may increase individual movements and elevate the risk of disease transmission between badgers and cattle. Field studies support this hypothesis, by demonstrating increases in badger group ranges and the prevalence of TB infection in badgers following culling. However, more evidence on the effect of culling on badger movements is needed in order to predict the epidemiological consequences of this control strategy. Here, analysis of the genetic signatures of badger populations in the RBCT revealed increased dispersal following culling. While standard tests provided evidence for greater dispersal after culling, a novel method indicated that this was due to medium- and long-distance dispersal, in addition to previously reported increases in home-range size. Our results also indicated that, on average, badgers infected with M. bovis moved significantly farther than did uninfected badgers. A disease control strategy that included culling would need to take account of the potentially negative epidemiological consequences of increased badger dispersal.     

A genetic analysis of body size in pink salmon (Oncorhynchus gorbuscha)

Two small-sized and two large-sized male pink salmon (Oncorhynchus gorbuscha) were mated to each of four females, producing eight families sired by small males and eight sired by large males. The juveniles were reared for 500 d after fry emergence. Juvenile weight in the two male size classes was similar until the spring of the year of maturity, when juveniles sired by large males grew faster than those sired by small ones. Heritability estimates of weight based upon the dam component of variance increased during 500 d of rearing from 0.4 to 0.8. Heritability of weight based upon the sire component of variance generally ranged between 0.1 and 0.3. The large variation in male body size in spawning pink salmon populations may have resulted from different male breeding strategies.     

Population structure of the echinoid Heterocentrotus mammillatus (L.) along the littoral zone of south-eastern Sinai

The population structure of the slate-pencil sea urchin Heterocentrotus mammillatus was studied along the southeastern coast of the Sinai peninsula. Evenly-distributed size classes were observed in populations occupying the forereef, while populations of this species from the reef slope and the back reef contained smaller proportions of small and medium-sized individuals. During the five years of study, growth rates and abundances of each size group were found to be stable. Analysis of size frequency distributions show that recruitment of H. mammillatus at the study area was regular and mortality rates were low during the second to fifth year of life and increasing later. This was supported by aging of dead individuals and observations indicating that large individuals were more susceptible to predation than smaller ones.     

Predicting the annual effective size of livestock populations

Effective population size (Ne) is an important parameter determining the genetic structure of small populations. In natural populations, the number of adults (N) is usually known and Ne can be estimated on the basis of an assumed ratio Ne/N, usually found to be close to 0.5. In farm animal populations, apart from using pedigrees or genetic marker information, Ne can be estimated from the number N of breeding animals, and a value of 1 is commonly assumed for the ratio Ne/N. The purpose of this paper is to show the relation between effective population size and breeding herd size in livestock species. With overlapping generations, Ne can be predicted knowing the number of individuals entering the population per generation and the variance of family size, the latter being directly related to the survival pattern (or replacement policy) in the breeding herd. Assuming an ideal survivorship leading to a geometric age distribution, it can be shown that the number of breeding animals tends to overestimate effective size, particularly in early-maturing species. The ratio of annual effective size to the number of breeding animals is shown to be equal to [1 + (a- 1)(1 - s)]2/(1 - s2), where a is the age at first offspring and s is the survival rate (including culling) of the parents between successive births. This expression shows to what extent inbreeding may be determined by demography or culling policy independently of the actual herd size. In many situations a fast replacement or an early culling will increase annual effective size. Consequences for the management of small populations are discussed.     

The conservation of the biomass density and the age structure of the populations

A study was made of populations in stationary equilibrium that satisfy the following conditions: (1) The birth rate is very large in relation to the capacity of the habitat. (2) The part of the mortality which is independent of age is easily measured and is found to be very high. For these populations the following conclusions were drawn from the experimental observations: (1) The populations in steady state show an inversely proportional relation between the maximum average age of its components and the mortality. (2) The biomass of a population in a steady state saturating a habitat remains constant in spite of changes in the mortality. (3) The population of organisms continually growing through life, whose steady-state equilibria are reached under conditions of high mortality are composed of great numbers of individuals with a small average size. The equilibria which are reached under conditions of low mortality are characterized by a small number of individuals with large average size.     

Ovarian activity and uterus organometry in delayed puberty gilts

About 30% of the total number of gilts selected for reproduction at the large breeding farm units in Vojvodina (Republic of Serbia) are culled due to prolonged pre-insemination anoestrus (estrus not detected until 8 mo of age). The aim of this study was to provide the answer to the following question: do the culling gilts reach cyclic ovarian activity at all? One hundred seventy five culled gilts in which external estrus manifestations were not detected by 8 mo of age were sacrificed and their reproductive organs were examined for determination of sexual maturity (ovaries exhibiting pre-ovulatory follicles 8 to 11 mm in diameter, corpora hemorrhagica, corpora lutea and corpora albicantia). Uterine weights and horn length were also determined. Functional ovaries were observed in 107 (61.1%) examined gilts, with 62 animals having one and 45 having two puberty ovarian cycles (57.9% and 42.1%, respectively). Pathomorphological changes which could result in prolonged pre-insemination anoestrus were not observed on the reproductive organs of sexually mature gilts. Our results indicate that most of the culling gilts have reached cyclic ovarian activity. The main reason for culling due to the absence of external estrus manifestations in sexually mature gilts could be inadequate estrus detection technology.     

Relatedness and competitive asymmetry – the growth and development of common frog tadpoles

Individuals can compete either through direct interference or uptake of limiting resources. If competing individuals are able to recognize their relatives, relatedness of competitors may evoke kin selection, which favours relatively even resource share among relatives. Resource competition is often size-symmetric, i.e. proportional to an individual's biomass, while interference competition is asymmetric giving large individuals a disproportionate advantage over small individuals. Kin-selection is predicted to reduce the intensity of direct interference and competitive asymmetry, leading to increased mean and decreased variation in individual size. We tested these predictions by investigating the effects of relatedness on age and size at metamorphosis in the common frog Rana temporaria tadpoles in a laboratory experiment. We reared related (full- and half-sibs) and unrelated tadpoles of different sizes (small, large, small and large together) at two densities until metamorphosis. Relatedness had little effect on mean growth, but it reduced size variation, as measured with coefficient of variation. Furthermore, there was a significant interaction between relatedness and density in size at metamorphosis, so that relatives always grew better in lower density, but growth was less affected by density among unrelated individuals. This indicates that the effects of relatedness on tadpole performance may be context dependent. Initial size differences in the mixed size treatment evened out during the course of the experiment, and initially small tadpoles were able to compensate the early growth losses, although it took longer for them to reach metamorphosis. We conclude that although relatedness may have rather small effects on the growth and development of R. temporaria tadpoles, it increases the symmetry of resource share decreasing between-individual variation in size at metamorphosis.     

Darwinian fitness, evolutionary entropy and directionality theory

Two recent articles provide computational and empirical validation of the following analytical fact: the outcome of competition between an invading genotype and that of a resident population is determined by the rate at which the population returns to its original size after a random perturbation. This phenomenon can be quantitatively described in terms of the demographic parameter termed "evolutionary entropy", a measure of the variability in the age at which individuals produce offspring and die. The two articles also validate certain predictions of directionality theory, an evolutionary model that integrates demography and ecology with population genetics. In particular, directionality theory predicts that in populations that spend the greater part of their life cycle in the stationary growth phase, evolution will result in an increase in entropy. These species will be described by a late age of sexual maturity, small progeny sets and a broad reproductive time-span. In populations that undergo large fluctuations in size, however, the evolutionary outcome will be different. When the average size is large, evolution will result in a decrease in entropy-these populations will be described by early age of sexual maturity, large numbers of offspring and narrow reproductive span but when the average size is small, the evolutionary outcome will be random and non-directional.