Indirect effects on fitness between individuals that have never met via an extended phenotype

Interactions between organisms are ubiquitous and have important consequences for phenotypes and fitness. Individuals can even influence those they never meet, if they have extended phenotypes that alter the environments others experience. North American red squirrels (Tamiasciurus hudsonicus) guard food hoards, an extended phenotype that typically outlives the individual and is usually subsequently acquired by non‐relatives. Hoarding by previous owners can, therefore, influence subsequent owners. We found that red squirrels breed earlier and had higher lifetime fitness if the previous hoard owner was a male. This was driven by hoarding behaviour, as males and mid‐aged squirrels had the largest hoards, and these effects persisted across owners, such that if the previous owner was male or died in mid‐age, subsequent occupants had larger hoards. Individuals can, therefore, influence each other's resource‐dependent traits and fitness without ever meeting, such that the past can influence contemporary population dynamics through extended phenotypes.     

围栏条件下岩松鼠对核桃的贮藏

许多动物都能够贮藏食物以应对一定时期的食物短缺。岩松鼠是中国特有的一种啮齿动物,主要分布于华北山地和丘陵地区,对于其食物贮藏行为还了解不多。我们在北京东灵山地区建立了半自然围栏,在围栏一角设置一木质巢箱供其休息,在围栏中心设一食盘(给食处),就岩松鼠对核桃(已预先标记)的贮藏特征进行了观察。每只受试动物在实验开始前6 h断食,于13∶ 00 左右,随机选择1 只岩松鼠,将其放入围栏中适应2 ～ 3 h。随后,在给食处放置20 枚已标记的核桃。于第二天同一时间进入围栏,检查并记录岩松鼠对核桃的处理情况,将埋藏、取食和剩余的核桃全部移出,另置20 枚新的核桃,继续实验。第三天,重复上述检查和记录,将岩松鼠及被其处理的核桃全部移出,清理巢箱、整理围栏。随后放入第二只岩松鼠,重复上述实验过程,如遇恶劣气候,则实验顺延,直至实验结束。结果表明:岩松鼠兼具集中贮藏和分散贮藏两种食物贮藏方式,并且分散方式是其主要的食物贮藏方式;岩松鼠在围栏中选择一定的位置贮藏食物;文中还讨论了可能影响岩松鼠食物贮藏的因素。     

岩松鼠的食物贮藏行为

食物贮藏是许多动物对不可预见的食物供应变化的一种重要适应.岩松鼠(Sciurotamias davidianus)为中国特有物种,广泛分布于华北地区的山地和丘陵地带.作者在北京市东灵山地区建造半自然围栏(4 m×3 m× 1 m),以核桃(Juglans regia)和山杏(Prunus armeniaca)种子为备选食物,对岩松鼠(12只)的食物贮藏行为进行了研究.数据的统计分析采用SPSS for Windows进行.研究结果表明1)岩松鼠表现出集中和分散两种食物贮藏方式,而分散贮藏是其偏好的贮藏方式;2) 当遇到贮藏食物被盗窃时,岩松鼠倾向于搬运更多的食物进行集中和分散贮藏;3)岩松鼠没有在食盘就地取食任何一种食物;把食物搬离后,岩松鼠所取食的山杏种子数量明显多于所取食的核桃数量;4)岩松鼠只选择核桃进行分散贮藏;5)岩松鼠对核桃的搬运距离大于山杏种子.本研究结果提示,在自然条件下,岩松鼠对核桃和山杏的天然更新起着不同的作用[动物学报 51(3)376-382,2005].     

Sensitivity to Seed Germination Schedule by Scatter‐Hoarding Pére David's Rock Squirrels During Mast and Non‐Mast Years

Mast seeding by oaks (Quercus) and other seed species has fundamental impacts on the behavior of individual scatter‐hoarding animals as well as their population and community dynamics. Scatter‐hoarding squirrels are highly sensitive to acorn germination schedule and stop germination by removing the embryo of non‐dormant acorns to prevent losses of energy and nutrients by rapid germination. However, we know little about how this behavior is affected by mast seeding. We investigated foraging decisions made by free‐ranging Pére David's rock squirrel (Sciurotamias davidianus) with three species that produce non‐dormant seeds and two species that produce dormant seeds (Fagaceae) during mast and non‐mast years in Central China from 2007–2010. Consistent with the food perishability hypothesis that squirrels make decisions to minimize the perishability of their caches, non‐dormant seeds were hoarded at a lower rate, but had a higher probability of embryo removal than dormant seeds. Compared with non‐mast years, a lower proportion of seeds were harvested during mast years, but a higher proportion of the harvested seeds were hoarded. In addition, the probability of embryo removal in the hoarded seeds was higher during mast years. Squirrels also dispersed seeds at shorter distances during mast years. Moreover, the interactions between mast seeding and seed germination schedule had significant effects on squirrel foraging decisions, including embryo removal. This study is the first to demonstrate that squirrels show greater sensitivity to seed germination potential when seeds are abundant.     

Experimental removals reveal dietary niche partitioning facilitates coexistence between native and introduced species

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Return of Fire as a Restoration Tool: Long‐Term Effects of Burn Severity on Habitat Use by Mexican Fox Squirrels

After decades of suppression, fire is returning to forests of the western United States through wildfires and prescribed burns. These fires may aid restoration of vegetation structure and processes, which could improve conditions for wildlife species and reduce severe wildfire risk. Understanding response of wildlife species to fires is essential to forest restoration because contemporary fires may not have the same effects as historical fires. Recent fires in the Chiricahua Mountains of southeastern Arizona provided opportunity to investigate long‐term effects of burn severity on habitat selection of a native wildlife species. We surveyed burned forest for squirrel feeding sign and related vegetation characteristics to frequency of feeding sign occurrence. We used radio‐telemetry within fire‐influenced forest to determine home ranges of Mexican fox squirrels, Sciurus nayaritensis chiricahuae, and compared vegetation characteristics within home ranges to random areas available to squirrels throughout burned conifer forest. Squirrels fed in forest with open understory and closed canopy cover. Vegetation within home ranges was characterized by lower understory density, consistent with the effects of low‐severity fire, and larger trees than random locations. Our results suggest that return of low‐severity fire can help restore habitat for Mexican fox squirrels and other native wildlife species with similar habitat affiliations in forests with a historical regime of frequent, low‐severity fire. Our study contributes to an understanding of the role and impact of fire in forest ecosystems and the implications for forest restoration as fire returns to the region.     

The placement, recovery, and loss of scatter hoards by eastern chipmunks,Tamias striatus

Although eastern chipmunks typically larder hoard food in theirburrows, some scatter hoarding occurs, especially by newly emergedjuveniles and by females with young. To examine patterns ofscatter hoard placement and their adaptive significance, weused standard food provisioning tests followed by continuousmonitoring to determine the longevity and fate of scatter hoards.Longevity of scatter hoards was low (median 74 min) and pilferagewas high (46%). Chipmunks placed scatter hoards away from thepatch, closer to their burrow and within the defended area ofprimary use. Scatter hoard placement was affected by the numberof competitors at the patch. However, juveniles and femaleswith young differed slightly in their responses. competitorsthat approached scatteihoards were sometimes chased away bythe scatter hoard's owner, and the scatter hoard was moved toanother location by the owner. Females with young recoveredtheir largest scatter hoards first, but there was little additionalpattern in scatter hoard recovery. An experiment using simulatedscatter hoards showed that scatter hoards farther from a patchof food lasted longer and that disturbing and marking scatterhoards reduced their longevity. These observations indicate:(1) that scatter hoard placement is more related to avoidingpilferage of completed caches than to rapidly sequestering fooditems from an ephemeral patch and (2) that optimal cache distributionmay be affected by the cache-defense ability of individuals,by the relationship between competitor density and cache securitynear the patch, and by the territorial behavior of neighboringconspecifics.     

Identifying key habitats for the conservation of Bonelli's Eagle Aquila fasciata using radiotracking

Identifying the priority habitats of endangered species is crucial to implementing effective conservation actions. We characterize the key habitats used by Bonelli's Eagle Aquila fasciata, an umbrella and flagship species that is endangered in Mediterranean countries. We radiotracked 17 breeding individuals (10 males and seven females) in Catalonia (NE Iberian Peninsula) and used compositional analysis to determine the key habitats in home‐ranges of both sexes. The main habitats identified within the home‐range area were scrubland, coniferous forests, cropland, sclerophyllous forests, rock outcrops and urban areas, with little difference in habitat use between the sexes. Bonelli's Eagles preferred rocky habitats as breeding areas and scrubland as foraging areas, as these hold the highest abundance of their main prey, Rabbits Oryctolagus cuniculus and Red‐legged Partridges Alectoris rufa. Habitat selection varied seasonally in foraging areas: scrubland was the most preferred habitat type during the breeding season, whereas rocky areas were preferred during the non‐breeding season (although scrubland was also highly selected). Urban areas were avoided both as breeding and as foraging areas. Home‐range size was inversely correlated with the proportion of scrubland, suggesting that this is a key habitat for Bonelli's Eagle. To conserve this species effectively, policies that ensure the preservation of the cliffs used as breeding sites, as well as suitable management of the scrubland used for foraging, should be implemented in the areas inhabited by this species. The promotion of traditional land uses and management techniques that will enhance open areas in Mediterranean landscapes should in the future play an essential role in the conservation of Bonelli's Eagle in Mediterranean habitats.     

Weak olfaction increases seed scatter‐hoarding by Siberian chipmunks: implication in shaping plant–animal interactions

Scatter‐hoarding of seeds by animals plays an essential role in seed dispersal of plants and in shaping plant–animal interactions in forest ecosystems, but the function of scatter‐hoarding behavior is still unclear. We hypothesize that weak olfactory cues between seeds and scatter‐hoarding animals would increase scatter‐hoarding. Using a rodent–plant system of Siberian chipmunks Tamias sibiricus and Korean pines Pinus koraiensis, we tested the effects on seed scatter‐hoarding intensity by measuring and modifying the seed odor intensities and the abilities of the animals to detect seed odor. Siberian chipmunks seemed to scatter‐hoard more seeds with weaker odor signals, and Siberian chipmunks with reduced olfactory ability scatter‐hoarded more seeds, supporting our hypothesis. Our studies suggest that olfaction may have played an important role in the evolution of the strength of seed odor and scatter‐hoarding behavior of animals, and in shaping plant–animal interactions.     

Evidence of Social Influences on Cache‐Making by Grey Squirrels (Sciurus carolinensis)

Many studies have found that scatter‐hoarding animals change their behaviour when storing food in the presence of conspecifics to minimize the likelihood that their caches will be pilfered; they refrain from caching, move away from conspecifics or choose visually obscured sites. This study reports the first evidence that the presence of conspecifics continues to influence the caching behaviour of a scatter‐hoarding mammal, the grey squirrel, after a suitable cache site has been selected and the hoarder is filling and covering its cache. Wild grey squirrels were filmed when storing preferred and less preferred nuts and when they were alone or with conspecifics present. In line with previous findings, squirrels spent longer travelling from the nut patch and were more vigilant when conspecifics were present. However, squirrels also spent longer disguising their caches and were more likely to stop digging and become vigilant when conspecifics were present than when they were alone. In particular, they were most likely to curtail their digging when storing their preferred nuts in the presence of conspecifics. The results indicate that caching squirrels remain sensitive to the presence of conspecifics until the cache is complete and that they respond flexibly to conspecifics according to the type of food they are storing.     

Food hoarding behaviour of large field mouseApodemus peninsulae

An important behavioural adaptation for animal species with variable or unpredictable food availability is storing food. Food availability for large field mouseApodemus peninsulae (Thomas, 1907) is not reliable. We conducted a series of tests with the large field mouse to determine food hoarding behaviour, response when their hoarded food was removed, and whether perishable foods were treated different than non perishable foods. The study was conducted in four semi-natural enclosures (4 × 3 × 1 m), established on the Donglingshan Mountain near Beijing, China. Thirteen large field mice were placed in enclosures and offered wild apricotPrunus armeniaca seeds and Liaodong oakQuercus liaotungensis acorns. Our results indicated that although large field mice hoarded seeds in larder and scatter patterns, they more frequently exhibited larder hoarding. Liadong oak acorns were generally consumed near the feeder, whereas apricot seeds were more frequently transported to the nest box. Only apricot seeds were scattered among hoard sites. When seeds were removed from hoarding sites the mice responded by taking increased amounts of seeds to their nest for larder and scatter hoarding. Hoarding sites were not randomly distributed throughout the enclosure.     

The anatomy of a range expansion: changes in cranial morphology and rates of energy extraction for North American red squirrels from different latitudes

Species with expanding ranges provide unique opportunities to examine environmentally induced adaptations in ecological traits and anatomical characteristics. Since the late 1800s, the North American red squirrel (Tamiasciurus hudsonicus) has expanded its range into the central hardwoods of the United States in conjunction with increasing agricultural fragmentation. We examined whether red squirrels from the central hardwoods (west‐central Indiana, USA) displayed differences in foraging behaviors and morphology relative to red squirrels from conifer‐dominated environments (upper peninsula of Michigan, USA), a biome in which red squirrels evolved. Specifically, we measured rates of energy extraction, variation in cranial morphology, and diet preference between red squirrels from both regions. In addition, we compared foraging behaviors of red squirrels from the central hardwoods to those of a competitor that coevolved with nut‐producing trees, the gray squirrel (Sciurus carolinensis). Red squirrels from Indiana and Michigan differed significantly in the efficiency with which they used food items, with individuals from each region extracting calories at a more rapid rate for items that were common in their region. The enhanced efficiency of southern red squirrels feeding on black walnuts (Juglans nigra) was correlated with geographic differences in cranial morphology; skulls of southern squirrels were larger, with longer jaws and higher metrics associated with greater mandibular force than northern squirrels. Contrary to our expectations, red squirrels from Indiana and Michigan did not differ qualitatively in preferences for food items, suggesting that diet choice may be governed by perishability of food items rather than by rates of energy extraction. Gray squirrels were more efficient than Indiana red squirrels in using all food items, and differed only slightly from red squirrels with regard to preference for food items. Measures of efficiency of resource use, after accounting for species‐specific metabolic requirements, suggest that red squirrels are unlikely to compensate ecologically for declining gray squirrel populations in fragmented portions of the central hardwoods, with potentially adverse effects for forest regeneration and succession. Our results demonstrate that invading species can display significant flexibility in adapting to new environments, but they may not be flexible enough to exploit resources in a manner comparable to native species.     

围栏条件下中华姬鼠和北社鼠对完好和虫蛀锐齿槲栎种子的取食和贮藏行为差异

正种子贮藏是啮齿动物利用食物资源的一种适应性行为(Vander Wall,1990)。经过长期的进化,啮齿动物形成了两种主要的贮藏食物行为:一是集中贮藏,即把收集的大量食物集中在其洞穴或临时栖息场所贮藏,通常有少量贮藏点,每个贮藏点有大量种子;二是分散贮藏,即把收集的种子分散贮藏在相对较大范围或其巢域周围,通常有大量贮藏点,但每个贮藏点仅贮藏约1～3粒种子。与集中贮藏相比,分散贮藏扩展了植物种子的分布范围,降低了种子被动物取食的概率。由于被分散贮藏的     

凉水自然保护区松鼠（Sciurus vulgaris）贮食生境选择

2003年10月~2004年4月,在黑龙江省小兴安岭凉水国家级自然保护区,应用跟踪观察法、样线调查法、样方调查法等研究方法,采用Vanderploeg和scavia选择系数Wi和选择指数Ei作为衡量指标,对松鼠贮食红松种子生境选择进行了研究。研究表明,松鼠贮食对生境具有选择性:以主要林型为划分标准,松鼠偏爱贮食生境依次为:原始红松林,云杉林,人工云杉林,针叶混交林,人工落叶松林,针阔混交林,阔叶混交林,次生白桦林和人工红松林。在原始红松林内,松鼠对微生境的利用存在选择性差异:松鼠对郁闭良好(郁闭度大于0.6)、灌丛密度中等、倒木和枯立木密度中等(1~5个)、盗食动物活动较弱(大林姬鼠Apodemus peninsulae为主要盗食动物)的原始红松林生境表现出较强的选择性(Ei>0.2);而对坡度小于5°、基质为霉菌土、倒木和枯立木密度较高(大于5个)、草本盖度较高、盗食动物活动中等(花鼠Eutamias sibiricus为主要盗食动物)的原始红松林生境表现出较强的负选择性(Ei<-0.2),对阴坡表现出强烈的回避性(Ei=-0.5368)。     

Diversifying Coevolution between Crossbills and Conifers

Coevolution between granivorous crossbills (Loxia spp.) and conifers has been a prominent process in the diversification of crossbills. A striking example occurs in western North America where coevolution between crossbills and Rocky Mountain lodgepole pine (Pinus contorta latifolia) is ongoing in isolated ranges without the crossbill’s dominant competitor for seeds, the red squirrel (Tamiasciurus hudsonicus). Preferential foraging by crossbills on lodgepole pine cones in the South Hills and Albion Mountains, two small mountain ranges in southern Idaho where red squirrels are absent, has led to the evolution of larger, thicker-scaled cones than in nearby ranges where red squirrels are present. This in turn has favored the evolution of larger-billed crossbills that have diverged from other crossbills in the region. However, such diversifying coevolution, resulting from geographic variation in the distribution of strongly interacting species, is vulnerable to species introductions. For example, the introduction of red squirrels caused the precipitous decline and perhaps extinction of the Newfoundland crossbill and perhaps a crossbill endemic to the Cypress Hills, Canada. In general, species introductions act to reduce the geographic variation in species interactions, which may be critical for the diversification of many taxa.     

Communal Nesting in Asocial Abert's Squirrels: the Role of Social Thermoregulation and Breeding Strategy

The social thermoregulation hypothesis states that endothermic species will communally nest to reduce energy expenditures on thermoregulation. The hypothesis predicts that the frequency of communal nesting should increase with decreasing ambient temperature. The potential costs of communal nesting (e.g., increased predation risk, resource competition, cuckoldry, parasite/disease transmission, or infanticide) could decrease the frequency of communal nesting especially for asocial breeding females with dependent offspring. We examined the effects of ambient temperature and seasonal reproductive activities on the probability of communal nesting in Abert's squirrels (Sciurus aberti) in the Pinaleño Mountains, Arizona. Most squirrels nested consistently with the same partner in mixed‐sex pairs. The proportion of individuals engaging in communal nesting increased with decreasing ambient temperature as predicted by the social thermoregulation hypothesis. The onset of the breeding season greatly reduced the proportion of individuals communally nesting. The negative relationship between ambient temperature and communal nesting supports the use of communal nesting in Abert's squirrels as a mechanism to reduce thermoregulatory costs during cold conditions. The abrupt drop in the frequency of communal nesting during the breeding season is likely due to female abandonment of this behavior. By avoiding communally nesting during the breeding season, females may prevent males from mating with them outside of mating chases, reduce resource competition, and protect offspring from infanticide, diseases, and parasites. Males may gain additional fitness benefits from nesting with females because familiarity with females increases dominance rank in mating activities.     

Exclusive core areas and intrasexual territoriality in Eurasian red squirrels (<Emphasis Type="Italic">Sciurus vulgaris</Emphasis>) revealed by incremental cluster polygon analysis

When animal home ranges overlap extensively in species lacking overt territorial behaviours, identifying exclusive core areas within individual ranges can be difficult. By analysing the size and overlap of successively smaller core areas among individual Eurasian red squirrels (Sciurus vulgaris), we determined exclusive areas within the home ranges of resident males and females. Possible effects of habitat composition and food supplies were explored by monitoring squirrels in different conifer forests and during years with low and high tree seed production. Using outlier-exclusive cores (OEC) revealed that the total ranges consisted of large sally zones (on average, 35% of the total minimum convex polygon [MCP] range) around home ranges with multi-nucleate cores. The mean OEC home range size did not differ between the sexes but was larger with poor food availability. Home ranges (99% incremental cluster polygons [ICP]) overlapped extensively between sexes (average overlap high food–low food: males by females 21–40%, females by males 43–45%) and among males (males by males 26–44%), while intrasexual overlap among females was low (9–10%). The overlap of inner cores among females rapidly approached zero, suggesting the intrasexual territoriality of 75% core areas. This was not the case among male squirrels, for which intrasexual overlap averaged only 4% at 50% but 18% at 75% core areas. Even the smallest inner cores had some degree of intersexual overlap, indicating that complete territoriality did not occur in this species. Female home ranges were more strongly affected by annual fluctuations in food supplies than male ranges. Females reduced the size of their food-based intrasexual territories when food availability increases. Males probably benefit from using larger home ranges and core areas, which overlap with the ranges of several females, by increasing their probability of successful mating.     

The effects of hoarding habitat selection of Eurasian red squirrels (Sciurus vulgaris) on natural regeneration of the Korean pines

Cone-cores discarded by Eurasian red squirrels were used to study the habitat selection of Korean pine-seeds hoarding, in forest patch Nos. 16 and 19 in Liangshui Nature Reserve, China. Ten transects with a total length of 15 km were uniformly set, and data from 343 valid samples were collected in a 369 hm² area. One hundred and eighty four were hoarding samples which were determined according to the cluster analysis based on the number of the cone-cores, while the other 159 were control samples. The principal component analysis, using 11 habitat factors, suggested that the distance from Korean pine forest, forest type, number of Korean pine seedlings, density and type of bush significantly influenced the habitat selection of hoarding by Eurasian red squirrels. The results of Bailey’s method indicated that the squirrels showed (1) preference for natural coniferous forest, natural fir and spruce forest and planted spruce forest; (2) avoidance of planted Korean pine forest and planted larch forest; and (3) random use of natural Korean pine forest. Moreover the distance from the Korean pines in the range of 150–600 m showed no effect on the habitat selection of hoarding by the Eurasian red squirrels. More than 50% of the cone-cores were discarded in either fringe or gap of the Korean pine forest with more cone-cores found at <300 m than at 300 m away (One-Way ANOVA; df = 3, 183, F = 5.76, p = 0.0009). This demonstrated that the Eurasian red squirrels could take the cone-cores out of the Korean pine forest. The density of bushes in samples of hoarding area was significantly lower than that in control samples (Kruskal–Wallis test; df = 1, χ² = 83.99, p < 0.0001). The number of the Korean pine seedlings in samples of hoarding area was significantly higher than that in the control samples (Kruskal–Wallis test; df = 1, χ² = 104.13, p < 0.0001). This illustrated that the hoarding habitat favoured the germination of the Korean pine seedlings. In conclusion the behavior of hoarding Korean pine seeds by the Eurasian red squirrels can promote the regeneration and dispersal of the Korean pines.     

Current and future habitat availability for Thick‐billed and Maroon‐fronted parrots in northern Mexican forests

Thick‐billed Parrots (Rhynchopsitta pachyrhyncha) and Maroon‐fronted Parrots (Rhynchopsitta terrisi) are the only parrots in Mexico found in high‐elevation coniferous forests. Both species are critically endangered due to logging, and climate change is expected to further reduce their available habitat. Our objectives were to assess the present and future availability of a suitable habitat for these parrots using ecological niche models. Future climatic scenarios were estimated by overlaying the present distributions of these parrots on maps of projected biome distributions generated using a North American vegetation model. Our climatic scenarios revealed that the distribution of key habitats for both parrots will likely be affected as the climate becomes more suitable for xeric biomes. The climate associated with coniferous forests in the current range of Maroon‐fronted Parrots is predicted to disappear by 2090, and the climate associated with the key coniferous habitats of Thick‐billed Parrots may contract. However, our results also indicate that suitable climatic conditions will prevail for the high‐elevation coniferous biomes where Thick‐billed Parrots nest. The degree to which both species of parrots will be able to adapt to the new scenarios is uncertain. Some of their life history traits may allow them to respond with a combination of adaptive and spatial responses to climatic change and, in addition, suitable climatic conditions will prevail in some portions of their ranges. Actions needed to ensure the conservation of these parrots include strict control of logging and integration of rapid response teams for fire management within the potential foraging ranges of nesting pairs. A landscape with a greater proportion of restored forests would also aid in the recovery of current populations of Thick‐billed and Maroon‐fronted parrots and facilitate their responses to climate change.