Effects of castration and home cage residency on aggressive behavior in rats

The effects of castration of both resident and intruder rats on territorial aggressive behavior were studied. The results suggest that residence in a home cage is more important than gonadal status in determining the outcome of an aggressive encounter. Resident rats were more likely to be dominant especially if they were intact. Intact residents directed less aggressive behavior toward castrated intruders than toward intact intruders. Intruder rats generally showed low levels of aggressive behavior and were only dominant when the resident had been castrated. Thus, the aggressive behavior of a male rat depends upon both his gonadal status and that of his opponent.     

河狸亲缘信息素的遗传力:遗传关系的信息是怎样编码的?

本研究利用几种亲缘关系对河狸 (Castorcanadensis)肛腺分泌物中的单个化合物和其整体组合的狭义遗传力进行了估算。使用气相色谱和质谱对河狸肛腺化合物进行定性和定量分析 ,发现了单个化合物的遗传力很低 ,但化合物的整体组合却显示有适度的遗传力。因此 ,我们认为亲缘关系的编码可能涉及多种化合物 ,并以数量和数字编码并用的方式进行     

Comments on the Systematics and Classification of the Beavers (Rodentia, Castoridae)

The systematics of the beavers (Castoridae) are reviewed and definitions are presented for each subfamilial group. Four subfamilies are recognized: primitive Agnotocastorinae (divided into two tribes, Agnotocastorini and Anchitheriomyini); burrowing beavers, Palaeocastorinae; giant beavers, Castoroidinae (containing two tribes, Castoroidini and Trogontheriini); and the Castorinae. The agnotocastorines are viewed as the ancestral group for all later subfamilies. The Palaeocastorinae is viewed as a side-branch, not ancestral or closely related to any of the later subfamilies. The Castorinae and Castoroidinae may represent a distinct clade united by dental features.     

Fish recruitment, dispersal, and trophic interactions in a heterogeneous lotic environment

I examine how dispersal of juvenile creek chubs (Semotilusatromaculatus) from beaver ponds into adjacent stream environments interacts with temporal abiotic variability to influence fish foraging, growth, and long-term persistence in the lotic ecosystem. Minnow trapping in upstream and downstream beaver ponds, along with weir traps used to monitor directional movement, indicated that most chubs colonized the stream from the downstream beaver pond. Large annual fluctuations in density of age 0 creek chubs occurred in the stream over a 10-year sampling period. Multiple regression analysis indicated that stream temperature, precipitation, and the density of reproductive creek chubs were not correlated with summer density of age 0 chubs in the stream. The factor most strongly associated with increased density of age 0 creek chubs was creation of the downstream beaver pond during the 6th–7th years of the study, suggesting dispersal from the pond was the primary factor determining age 0 fish density in the stream. Most individuals in the strong year classes neither persisted in the stream through their first winter nor resulted in an increased abundance of older age classes in later years. Comparison of age 0 fish density in summer to the proportion of fish surviving to age 1 in spring suggested that overwinter mortality was density dependent. Furthermore, a comparison of the size structure for age 0 individuals in summer to age 1 individuals the following spring indicated that winter mortality was size dependent. Experiments in an artificial stream adjacent to the natural channel revealed that fish growth was strongly density dependent, decreasing as fish density increased across both spring and summer, and elevated and low discharge. The decline in invertebrate prey captured by the fish and the subsequent decline in fish growth appeared to be particularly pronounced under low discharge in summer. Changes in juvenile creek chub density had no significant effect on benthic insect or crustacean abundance, suggesting that exploitative competition for limited invertebrate drift resources was a more important cause of density- dependent growth than depressed local benthic invertebrate abundance. These results suggest that lotic regions adjacent to beaver ponds act as potential reproductive “sinks” for dispersing juveniles confronting seasonal and flow-mediated restrictions on resource acquisition and growth, and the occurrence of seasonal bottlenecks to their survival, especially harsh winter conditions. Received: 9 September 1996 / Accepted: 8 August 1997     

Rats are not the only introduced rodents producing ecosystem impacts on islands

In addition to rats, nutria (Myocastor coypus) and the North American beaver (Castor canadensis) have certainly caused damage at an ecosystem level when introduced to islands, in both cases primarily by ecosystem engineering. Of other introduced rodents successfully established on islands, the gray squirrel (Sciurus carolinensis) may be in the process of damaging entire forest ecosystems, particularly by bark-stripping. Though introduced muskrats (Ondatra zibethicus) have had ecosystem-level impacts in continental Europe, their impact on islands worldwide to which they have been introduced has been very limited. The North American red squirrel (Tamiasciurus hudsonicus) and Barbary ground squirrel (Atlantoxerus getulus) have each had substantial impacts when introduced to particular islands, but for neither species have these impacts yet been demonstrated to spread through an entire ecosystem. Introduced house mice (Mus musculus) may well generate ecosystem impacts on remote islands lacking rats, and it is possible that explosions of house mice on islands after rat eradication, a common occurrence, will lead in some instances to ecosystem impacts.     

The application of environmental ethics in biological conservation: a case study from the southernmost tip of the Americas

Biological conservation is not only about facts and technical measures concerning ecology, rather it must also consider values. This pertains to both the balancing of various human interests and also to the ethical evaluation of human actions towards nature. Here we discuss how environmental ethics can be incorporated into conservation decisions, and what implications the inclusion of ethical valuation has for the practice of conservation biology. While this is done mostly on a rather abstract level, we illustrate this here by applying ethical theory to a case study: the options for management of the introduced North American beaver (Castor canadensis) in the very south of Chile (Navarino Island). The beaver is an exotic species to the area and has substantially altered the ecological systems of the region. We discuss different options for dealing with the beaver (eradicate, control, tolerate, promote) from the viewpoint of anthropocentric environmental ethics and biocentric ethics. The results of our analysis demonstrate the value of ethical discussions in clarifying and underpinning arguments for and against specific actions. At the same time, they also show that ethical arguments do not decrease the need for sound scientific data but, on the contrary, may even increase this demand. We also highlight that the conclusions regarding adequate actions to be taken vary depending on the specific ethical theory embraced.

Interactions between cottonwood and beavers positively affect sawfly abundance

Abstract.  1. Cottonwood ( Populus spp.) are the dominant tree type in riparian forests of the western U.S.A. In these riparian forests, the beaver ( Castor canadensis ) is a major ecosystem engineer that commonly browses cottonwood, resulting in distinct changes to plant architecture. Here the hypothesis that beaver herbivory indirectly affects the distribution of a keystone leaf-galling sawfly through architectural changes in cottonwood was examined.
2. It was found that: (a) beaver herbivory of cottonwood results in an increase in average shoot length over unbrowsed cottonwood; (b) sawfly galls were up to 7–14 times more abundant on browsed cottonwood than unbrowsed cottonwood; and (c) sawfly gall abundance was correlated positively with changes in shoot length after beaver herbivory. Together these data show that the individual and combined effects of cottonwood and beaver herbivory increase shoot length, positively affecting sawfly abundance.
3. Because herbivores are a ubiquitous component of most ecosystems, we argue that the indirect effects of herbivory on plant quality, and subsequently other herbivores, may be as important as environmental variation.     

Responses of wolf feeding habits after adverse climatic events in central-western Belarus

Many studies have investigated the ecology of wolf populations of Eurasia, showing that although wolves are mostly opportunistic in seeking meso-large enough mammalian prey, they can also be selective, depending on local availability of prey and their population biomass. Yet prey preferences of the wolf have been poorly evaluated in situations of complex predator/prey systems because such ecological situations are extremely rare in Europe. In particular, the role of beaver is poorly known due to the extreme decline in its range and population over the last few centuries.We conducted a 15-year study (1999–2014) of wolf Canis lupus diet in the Naliboki forest of central-western Belarus to determine the dietary responses of the wolf population in a context of a rich prey supply (beaver 650 inds/100 km², elk 47 inds/100 km², red deer 98 inds/100 km, roe deer 398 inds/100 km², wild boar 234 inds/100 km²). The bison, although present, is not preyed on. We compared the seasonal and annual diet variations of both wolf adults and pups, by scat analysis and hair identification. In winter 2012–2013, the winter was quite harsh with a long period of snow, which severely affected the roe deer and wild boar populations. Five severe summer droughts also occurred (1999, 2001, 2002, 2004 and 2013), greatly decreasing the water level in rivers and canals. We took advantage of these stressful events to evaluate the diet responses of the wolves.In “normal” years, we identified 11 food categories, essentially beaver and medium-sized ungulates (66%), and large ungulates to a lesser extent (9% in summer, 20% in winter). The adults were found to selectively supply pups with beaver, probably because of its easy transportability. Beaver consumption also increased during summer droughts when water levels were very low. After the harsh winter of 2012–2013, which was followed by a sharp decline in medium-sized prey, we observed a shift in the winter diet breadth of the wolves towards greater consumption of both large wild ungulates and small carnivores. We concluded that:1. Beaver is a functional element in wolf ecology, as a primary food for adults and pups;2. A large range of available prey species is important to maintaining a viable wolf population in cases of extreme climatic events.     

The beaver's reconquest of Eurasia: status, population development and management of a conservation success

Overhunting reduced Eurasian Beaver (Castor fiber) populations to c. 1200 animals, in eight isolated populations, around the end of the 19th century. Protection, natural spread and reintroductions led to a powerful recovery in both range and populations during the 20th century, which continues at a rapid pace. The minimum population estimate is 593 000. There are also c. 12 500 North American Beaver (C. canadensis) established in Finland and Russian Karelia; however, other populations of C. canadensis introduced in Austria, Poland and France ap‐pear to be extinct. Castor fiber is now established throughout Europe with the exception of the British Isles, Iberia, Italy and the southern Balkans; reintroductions are continuing. Considerable further expansion in range and population, especially in western Europe and the lower Danube basin, can be expected. If current trends continue, C. fiber will, within a few decades, be a fairly common mammal in much of Europe. Following initial recolonization, populations typically show a pattern of rapid range extension within a watershed, followed only later by rapid population growth, and a barrier effect of watershed divides, which can be strongly isolating where physical or habitat barriers (such as mountains or intensive farmland) intrude between watersheds. Management of beaver distribution should therefore operate at the watershed scale, except where large human‐made dams form significant bar‐riers to spread. The period of rapid population increase, if unchecked, leads to a phase of population decline as marginal habitats are occupied and exhausted. This coincides with a peak in conflicts with human land‐use interests. A regulated hunting take of healthy beaver populations is recommended as the optimal management regime in managed landscapes. Early provision of interpretation and public viewing opportunities has been a feature of several recent reintroductions. This provides a benefit to the local economy through wildlife tourism, and helps foster positive attitudes to beavers.