Data logging of body temperatures provides precise information on phenology of reproductive events in a free-living arctic hibernator

Precise measures of phenology are critical to understanding how animals organize their annual cycles and how individuals and populations respond to climate-induced changes in physical and ecological stressors. We show that patterns of core body temperature (T _b) can be used to precisely determine the timing of key seasonal events including hibernation, mating and parturition, and immergence and emergence from the hibernacula in free-living arctic ground squirrels (Urocitellus parryii). Using temperature loggers that recorded T _b every 20 min for up to 18 months, we monitored core T _b from three females that subsequently gave birth in captivity and from 66 female and 57 male ground squirrels free-living in the northern foothills of the Brooks Range Alaska. In addition, dates of emergence from hibernation were visually confirmed for four free-living male squirrels. Average T _b in captive females decreased by 0.5–1.0°C during gestation and abruptly increased by 1–1.5°C on the day of parturition. In free-living females, similar shifts in T _b were observed in 78% (n = 9) of yearlings and 94% (n = 31) of adults; females without the shift are assumed not to have given birth. Three of four ground squirrels for which dates of emergence from hibernation were visually confirmed did not exhibit obvious diurnal rhythms in T _b until they first emerged onto the surface when T _b patterns became diurnal. In free-living males undergoing reproductive maturation, this pre-emergence euthermic interval averaged 20.4 days (n = 56). T _b-loggers represent a cost-effective and logistically feasible method to precisely investigate the phenology of reproduction and hibernation in ground squirrels.     

Sexually mature and immature yearling male European ground squirrels: a comparison of behavioral and physiological parameters

Early puberty may increase lifetime reproductive success, but may also entail diverse costs. In male European ground squirrels (Spermophilus citellus), age at sexual maturity varies among individuals. We compared sexually active and inactive yearling males under standardized conditions in outdoor enclosures. Non-reproductive yearling males hibernated significantly longer than mature males and emerged when the mating period had already started. Testosterone concentrations peaked in the precocious males during premating and mating, and were depressed in the non-reproductive individuals throughout the study period. Emergence body mass was similar in both groups, although sexually immature males were significantly heavier at the end of the active season. Additionally, non-reproductive yearlings grew faster than precocious individuals. Male–male aggression peaked during mating and the following 4 weeks. Intense aggressive interactions like chases and fights were mostly initiated by reproductive males and were directed towards mature competitors. Aggressive behavior in immature males was mainly expressed as spatial displacements. Non-agonistic interactions with females were only observed in sexually active males. Concentrations of fecal cortisol metabolites did not differ between the two male groups and were elevated in the second half of the active season. Leucocyte numbers were reduced during mating in mature males, whereas in immature animals, cell numbers did not change significantly. Our results indicate that early puberty in European ground squirrels involves lower growth rates, high intrasexual aggression, lower prehibernatory body mass, and probably worse immunological condition during mating.     

Changes in various plasma lipid components, glucose, and insulin in Spermophilus lateralis during hibernation

This study evaluated fat mobilization as related to gluconeogenesis in two age groups of hibernating golden-mantled ground squirrels (Spermophilus lateralis). Our experimental group consisted of a total of 16 male and 15 female squirrels. Plasma samples were collected from selected animals being killed weekly from January to March, and the concentration of triglycerides, glycerol (GY), free fatty acids (FFA), total cholesterol, lipase activity, glucose, and insulin, were determined by biochemical assays and radioimmunoassay. Our results showed a mean FFA/GY ratio of five, which was higher than the predicted value of three, suggesting a significant depletion of GY and an enhanced rate of gluconeogenesis via GY to maintain glucose homeostasis in the hibernating animals. The factor of age did not significantly affect plasma lipid components. However, in the male group, plasma glucose levels were significantly higher for adults than for juveniles. Overall, females had significantly higher plasma glucose levels than males (150 ± 11 vs. 110 ± 8 mg%, P < 0.05). In the adult group, a gender influence was also seen on plasma insulin levels, with females' being higher than males' (66 ± 13 vs. 25 ± 3 μIU/ml, P < 0.01). We suggest that during hibernation, female squirrels may have a higher rate of lipolysis and gluconeogenesis along with a lower glucose utilization than their male counterparts. Additionally, adult females may exhibit a higher peripheral insulin resistance during hibernation than adult males, a possibility which merits further study.     

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.     

Male red deer (<Emphasis Type="Italic">Cervus elaphus</Emphasis>) dispersal during the breeding season

Breeding dispersal can be of significant ecological and evolutionary importance. Yet, it is seldom considered in mammals. I present data on male red deer (Cervus elaphus) movements between sub-populations in southern Sweden during the rut. I investigated whether these movements could be breeding dispersal driven by mate competition. During the ruts of 1998–2009, I recorded 91 movements of males. The longest movement distance was 18.5 km. Dispersal was not restricted to yearlings or sub-adults, but also observed among adult stags. Of 91 movements observed, 7 were made by yearlings, 46 by sub-adults and 38 by adults. There was a significant move among yearlings and sub-adults towards areas with a higher ratio of females/adult males and towards areas with more females. The movements between rutting areas thereby seemed driven by sexual competition.     

The Social Organization of the Cape Ground Squirrel (Xerus inauris; Rodentia: Sciuridae)

The Cape ground squirrel (Xerus inauris) of southern Africa is a tropical species that does not hibernate. Field observations using scan and all-occurrence sampling revealed that this species was highly social. Female Cape ground squirrels formed social units of related females and their subadult young, as is typical for other ground squirrels. Female social groups were usually composed of 2–3 adult females and 2–3 subadults of either sex. Members of these female social groups shared sleeping burrows and feeding ranges. Female social groups did not cooperatively defend their feeding ranges from adjacent groups in other burrow clusters. Interactions within female social groups were highly amicable, and no dominance hierarchy was evident. Males in this species also lived in groups. These all-male bands of up to 19 individuals lived almost independently from female groups. The entire male band shared one home range, although ephemeral sub-bands were formed daily. The composition and size of these sub-bands changed daily. Interactions among males, which were largely amicable, included allogrooming and sleeping together. Analysis of interactions within the band indicated a stable, linear, dominance hierarchy among males. Dispersal in this species appeared to be male biased as is typical of other ground-dwelling squirrels, with males dispersing at reproductive maturity. Males joining male bands were thus dispersers and were not likely to be closely related. Sociality in the Cape ground squirrel may be summarized as highly social female kin clusters and associated social non-kin bands of males.     

Effects of spatial variation in food availability on spacing behaviour and demography of Eurasian red squirrels

In heterogeneous habitats with limited resources, spacing behaviour will affect individual variation in breeding success and density of populations, and is thus of general interest to ecologists. We investigated how red squirrels Sciurus vulgaris adapt their social organisation to tine‐grained heterogeneity in habitat quality, studying spacing behaviour, habitat use and population dynamics in a forest in north Italy, characterised by a mosaic of high‐quality (chestnut‐pine) and poor‐quality patches. We compared the data with those from more homogeneous broadleaf and mixed woodlands with similar overall tree seed abundance (“stable” habitats). Squirrels lived at lower densities (pre‐breeding density 0.39‐0.58 ha^‐1) than in “stable” habitats, although breeding rate was not reduced. Female breeding success was related to being primiparous as yearlings, and increased with body mass and proportion high‐quality habitat in the home range. Persistency rate of females was as in stable habitats, It was higher than male persistency, but immigration and recruitment rates were male biased, resulting in even sex‐ratio. All residents occupied high‐quality patches, and no subadults established a permanent home range in poor‐quality habitat. Home range and core‐area size was typically larger in males than in females and a male's core‐area overlapped those of other males and of females. Female core‐areas were overlapped by males but not. or very little, by other females (intrasexual territoriality). Home ranges, or core‐areas, were not smaller than in “stable” habitats, nor did we find a higher degree of core‐area overlap. We conclude that in patchy habitats dominant, resident red squirrels exclude dispersing animals from preferred, high‐quality habitat, producing a spacing pattern referred to as ideal despotic distribution, and that poor patches were only used temporarily by transient individuals, resulting in a reduction of density in comparison to populations in “stable” habitats.     

Proportion of mated females, female mating experience, and sex ratio of the osmund sawfly, Strongylogaster osmundae (Hymenoptera, Tenthredinidae)

The proportion of mated females (M _f) of the osmund sawfly, Strongylogaster osmundae, and the sex ratio of the eggs they deposited (r, proportion of males) were estimated in the wild by collecting egg masses. The proportion of mated females at oviposition varied from 0 to 1.0. M _f was high (often 1.0) among the females that emerged after hibernation, and lower in the subsequent generations. Mated females of the hibernated generation deposited equal numbers of eggs of both sexes. Mated females of the first and subsequent generations produced more female than male eggs. These results qualitatively agreed with the prediction provided by an evolutionarily stable strategy (ESS) model (if M _f < 1 then r < 0.5). However, the quantitative prediction provided by the model [M _f (1 − r) = 0.5] was not always observed in the wild, especially where the population density and M _f were high. The value of r was often lower than the predicted one. The following simple hypothesis was tested by experimentation: “Females that encounter males frequently estimate the proportion of mated females to be high and deposit eggs with a 1:1 sex ratio.” However, results did not support this hypothesis. Females that copulated soon after emergence and were courted by males two or more times did not show a higher offspring sex ratio than those which mated 1 or 2 days after emergence and experienced no other sexual encounter. Another mechanism for determination of r is suggested, and the reason why the population sex ratio of sawflies is often female-biased (r < 0.5) is discussed.     

Female-biased operational sex ratio of sexual host fish in a gynogenetic complex of Carassius auratus

To study the coexistence of sexual and gynogenetic forms, we examined the population structure of a gynogenetic complex of the Japanese crucian carp, Carassius auratus Temminck et Schlegel, during the April–June reproductive season by collecting 1225 mature fish that migrated from Lake Suwa to a tributary river for spawning. There were more sexual fish (about 80%) than gynogenetic fish in this complex, and the operational sex ratio in the sexual form was female biased (males were about 20%). Mean standard length and body weight of sexual females were larger than those of sexual males. Sex ratio was male biased in smaller fish (standard length, <8.5 cm) but female biased in larger fish (standard length, ≥8.5 cm). We determined age by scale ring marks; the average age of sexual females was higher than that of males, but there was no significant difference in the average age between sexual and gynogenetic females. Sex ratio in the sexual form was more female biased for old than for young fish, and the mean size of sexual females was larger than that of males of the same age. The clear female-biased sex ratio and age difference between sexual females and males can be explained either by (1) higher mortality of males or by (2) female-biased sex allocation. The latter process reduces the disadvantage of sex and contributes to the coexistence of sexual and gynogenetic forms. Received: November 24, 2000 / Accepted: March 6, 2001     

Wild Capuchins Show Male-Biased Feeding Tool Use

Relatively few studies have explored sex differences in the use of foraging tools among primates other than apes. Although male primates are thought to be more innovative, researchers have reported a female sex bias in the use of feeding tools in wild chimpanzees. We investigate here the nature and extent of sex differences in foraging tool use over 12 mo in a free-ranging group of bearded capuchins (2 males, 5 females, and 3 juveniles) living in the dry Caatinga forests of the Serra da Capivara National Park, Piaui, Brazil. These capuchins used 3 major types of feeding tools: 1) tools for probing; 2) tools for pounding/cracking; and 3) digging stones to extract tubers or roots. Adult males performed 63% (n = 134) of all events of tool use and used tools significantly more frequently than did females, although male bout lengths across all tools (57 s ± 7.9 SE) were equivalent to those of adult females (47.3 s ± 12.6 SE). Both sexes used digging and cracking tools, although at different rates, whereas adult males used sticks to probe for prey and other rewards far more than females. Differential opportunities to use tools were not apparent: >71% of tool-use events occurred on the ground, and males and females spent equal time on the ground. We suggest that sex differences in tool use may function as opportunities for male signaling of investment quality.     

Determinants of reproductive success in female Columbian ground squirrels

Summary We studied the reproductive success of female Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta for nine years. We defined reproductive success as the number of offspring surviving their first hibernation, classified as yearlings. The number of weaned juveniles explained one third of the variance in number of yearlings at emergence from their first hibernation the following spring, and much of the variance in individual reproductive success originated after weaning. Weight of adult females at emergence from hibernation was correlated with annual reproductive success. The mother's survival beyond weaning and the subsequent winter's snow accumulation had positive effects on annual reproductive success, whereas population density and summer temperature had negative effects. We found no effects on annual reproductive success of date of litter emergence, weight at emergence as a yearling, presence or absence of adult kin, distance from the natal site, location within the study area, winter temperature or summer precipitation. Age of first breeding did not affect lifetime reproductive success, which ranged from 0 to 19 yearlings produced over a lifetime. The greatest source of variation in lifetime reproductive success for females surviving to breeding age was offspring survival, followed by reproductive lifespan.     

Intraspecific differences in the pattern of hibernation in the ground squirrelSpermophilus beldingi

Summary Intraspecific differences in the patterns of heterothermy were found in captive Belding's ground squirrels that hibernated undisturbed at ambient temperatures of 5°C, 10°C, and 15°C. The timing of all entrances into and arousals from hibernation was determined from records of copper-constantan thermocouples that were mounted on the floor of each animal's nest box and connected to continuously recording potentiometers. In the absence of food, large adult males terminated hibernation spontaneously in the spring. In contrast, females and small non-breeding males (yearlings) did not stop hibernating but instead they shortened their bouts of torpor in the spring so that they aroused every three or four days. This interval of frequent arousals, termed the emergence period, lastel until the squirrels became emaciated, and it was only in the 2 or 3 weeks preceeding death (starvation period) that arousal frequency once again decreased towards midwinter values (Fig. 3). These animals terminated hibernation when fed during the emergence or starvation periods, but they were able to resume torpor if that feeding lasted less than a week.Termination of hibernation and reproductive development in males were related to the size of the animals, not their age. Males two years and older which did not deposit normal quantities of fat were like yearlings in that they had open-ended hibernation seasons and showed little testicular enlargement. Likewise, juvenile males that grew to near adult size in their first summer spontaneously terminated hibernation and had well developed testes like most older individuals. In addition, both the frequency and duration of arousals in the emergence period were related, in part, to the extent of the animals' fat reserves, such that large squirrels spent more time at high body temperatures than small individuals (Figs. 5, 6). This trend was most pronounced at high ambient temperatures.These intraspecific differences in hibernation physiology are consistent with the sex and agerelated differences in the timing of emergence above ground in nature. The increase in the time spent euthermic in the spring isinterpreted as an adaptation for increasing the opportunities for environmental assessment. The intraspecific differences in the extent of this euthermia appear to be associated with differences in the balance between the energy supplies available to an animal and its need to accelerate the use of that energy (i.e., arouse) in order to achieve an early and accurately-time emergence from the hibernaculum.     

Hibernating patterns of free-ranging Columbian ground squirrels

Summary The patterns of torpor and euthermy during hibernation was documented for 28 free-ranging Columbian ground squirrels (Spermophilus columbianus) fitted with temperature-sensitive radio transmitter collars. Adult males began hibernation earlier, were euthermic for a greater proportion of the hibernating season and emerged earlier than other age and sex classes. The patterns of hibernation of adult females did not differ significantly from those of juveniles. Emergence from the hibernaculum was preceded by a long (3–12 d) euthermic interval in adult males but not in adult females or juveniles. Changes in soil temperature did not appear to initiate emergence. The greater time spent euthermic by adult males is interpreted as a significantly greater energy cost of hibernation for adult males than for other age and sex classes. The benefits offsetting these costs may be increased reproductive potential in spring and avoidance of predation in late summer.     

Variably male-biased sex ratio in a marine bird with females larger than males

When the costs of rearing males and females differ progeny sex ratios are expected to be biased toward the less expensive sex. Blue-footed booby (Sula nebouxii) females are larger and roughly 32% heavier than males, thus presumably more costly to rear. We recorded hatching and fledging sex ratios in 1989, and fledging sex ratios during the next 5 years. In 1989, the sample of 751 chicks showed male bias at hatching (56%) and at fledging (57% at ˜90 days). Fledging sex ratios during the five subsequent reproductive seasons were at unity (1 year) or male-biased, varying from 56% to 70%. Male bias was greater during years when mean sea surface temperature was warmer and food was presumably in short supply. During two warm-water years (only) fledging sex ratio varied with hatching date. Proportions of male fledglings increased with date from 0.48 to 0.73 in 1994, and from 0.33 to 0.79 in 1995. Similar results were obtained when the analysis was repeated using only broods with no nestling mortality, suggesting that the overall increase in the proportion of males over the season was the result of sex ratio adjustments at hatching. The male-biased sex ratio, and the increased male bias during poor breeding conditions supports the idea that daughters may be more costly than sons, and that their relative cost increases in poor conditions. Received: 3 February 1998 / Accepted: 12 September 1998     

Brood sex ratio in the Kentish plover

How and why do the mating opportunities of males and femalesdiffer in natural population of animals? Previously we showedthat females have higher mating opportunities than males inthe Kentish plover Charadrius alexandrinus. Both parents incubatethe eggs, and males provide more brood care than females; thusit is not obvious why the females find new mates sooner thanthe males. In this study we investigated whether the sex-biasedmating opportunities stem from biased offspring sex ratios.We determined the sex of newly hatched, precocial chicks usingCHD gene markers. Among fully sexed broods, 0.461 ± 0.024(SE) of chicks (454 chicks in 158 broods) were male, and thissex ratio was not significantly different from unity. The proportionof males at hatching decreased significantly over the breedingseason, which occurred consistently in all 3 years of the study.Large chicks were more likely to be males than females. Neitherparental age nor body size of male and female parents was relatedto brood sex ratio. We also sexed a number of chicks that werecaught after they left their nest (range of estimated ages 0–17days) and found that the proportion of males increased withbrood age. This relationship remained highly significant whencontrolling statistically for hatching date. As brood size decreaseddue to mortality after the chicks left their nest, these resultssuggest that the mortality of daughters was higher than thatof the sons shortly after hatching. Taken together, our resultsshow that the female-biased mating opportunities in the Kentishplover are not due to biased brood sex ratio at hatching but,at least in part, are due to female-biased chick mortality soonafter hatching.     

The effect of drought stress on the sex ratio variation ofSilene otites

Under dry environmental conditions the sex ratio of many dioecious plants is male-biased, which is usually explained by the higher susceptibility of females to drought stress. We investigated if spatio-temporal variation in the sex ratio ofSilene otites could be explained by the higher sensitivity of female plants to drought stress as compared to males. Long-term field observations, however, did not support this hypothesis. The sex ratio in 34 patches at the study site in Central Germany changed from slightly female biased in 1994 to strongly male-biased in 1997 and 1998. The interannual change in the proportion of plants that were female was positively correlated with the number of days with soil-water deficit in the late summer, suggesting higher mortality in males than in females under drought stress. In two closely studied patches, mortality in males was also higher than in females, although this difference could not be related to drought stress. These field observations were supported by an experiment with potted plants in two climate chambers, in which male mortality was higher during a three-week period without water supply. We conclude that the often reported male bias in patches ofS. otites is not caused by sexual differences in the sensitivity to drought stress. Field data in this study, however, suggest that maleS. otites plants flower earlier than females, which causes a shift in sex ratio to more male bias among flowering plants.     

Parameters of Mating Effort and Success in Male European Ground Squirrels,Spermophilus citellus

Behavioural and physiological changes during the reproductive period were documented in male European ground squirrels including: initiated conflict, scent marking, locomotion and range size, as well as testis size, scrotal pigmentation, testosterone levels and changes in body mass. Spring emergence dates in adult males varied but preceded those of females. Gonadal maturation was complete in adult males at emergence. Most yearlings did not mature and emerged with females. After a quiescent premating phase, male range, range overlap, conflict rates and locomotion increased at female emergence. The synchrony of females, their small ranges and short latencies to ovulation produced a highly male-biased operational sex ratio (OSR) and potential for scramble competition polygyny. In contrast to other ground squirrel species, each female apparently mated with only a single male. Scramble competition did appear to occur, in that males tried to contact as many females as often as possible before copulation. Females placed high temporal prerequisites on males. Costs of scrambling were documented by body mass loss during mating, which covaried with the number of ‘acquired’ females. Testicular regression occurred earlier, and fattening, moult and onset of next hibernation were delayed in successful males. The determinant factor in these costs was found to be mass loss intensity during the main mating period. Surprisingly, this factor was best related to feeding changes and not to locomotion or aggression. Time budget constraints perhaps imposed by the female, with compounding influences of exercise and stress effects of conflict, then negatively affected ensuing seasonal activities. The individual changes may adversely affect individual survivability and/or future reproductive success.     

Sexually mature and immature yearling male European ground squirrels: A comparison of behavioral and physiological parameters

Early puberty may increase lifetime reproductive success, but may also entail diverse costs. In male European ground squirrels (Spermophilus citellus), age at sexual maturity varies among individuals. We compared sexually active and inactive yearling males under standardized conditions in outdoor enclosures. Non-reproductive yearling males hibernated significantly longer than mature males and emerged when the mating period had already started. Testosterone concentrations peaked in the precocious males during premating and mating, and were depressed in the non-reproductive individuals throughout the study period. Emergence body mass was similar in both groups, although sexually immature males were significantly heavier at the end of the active season. Additionally, non-reproductive yearlings grew faster than precocious individuals. Male–male aggression peaked during mating and the following 4 weeks. Intense aggressive interactions like chases and fights were mostly initiated by reproductive males and were directed towards mature competitors. Aggressive behavior in immature males was mainly expressed as spatial displacements. Non-agonistic interactions with females were only observed in sexually active males. Concentrations of fecal cortisol metabolites did not differ between the two male groups and were elevated in the second half of the active season. Leucocyte numbers were reduced during mating in mature males, whereas in immature animals, cell numbers did not change significantly. Our results indicate that early puberty in European ground squirrels involves lower growth rates, high intrasexual aggression, lower prehibernatory body mass, and probably worse immunological condition during mating.     

Sex ratio and gender-dependent neighboring effects in <Emphasis Type="Italic">Podocarpus nagi</Emphasis>, a dioecious tree

We analyzed sex ratio, growth rates, and spacing among individuals of Podocarpus nagi, a dioecious tree, on Mt. Mikasa, Nara City, Japan. The sex ratio of reproductive trees ≥ 5 cm in stem diameter at breast height (dbh, 130 cm above ground level) was significantly male-biased. The sex ratio was male-biased in the < 20 cm and ≥ 50 cm size classes, while it did not depart from 1:1 in the 20 ≤ dbh < 50 cm class. Growth rate varied with tree size in males but not in females. The precocity and vigor of males suggests that differences in reproductive costs between sexes induce the biased sex ratio. Random labeling tests on the positions of reproductive trees showed that in the < 30 cm class, males and females were distributed randomly and independently from each other. In the ≥ 30 cm class, males were significantly clumped, whereas females were randomly distributed. Males and females showed significant repulsion, i.e., a spatial segregation of sexes. Both intra- and intersexual effects on the growth rate of crowding by neighbors were significant for females, but not for males. Maximum competitive interference was observed at a distance of 5 m, which corresponded approximately to the radius of clumps of large males and to the significant repulsive distance between large males and females. These results suggest that sexual differences in sensitivity to local crowding are related to the formation of gender-dependent spatial patterns. Formation of female-repulsive male clumps and a male-biased sex ratio may intensify the decreased probability of regeneration near males, as suggested by the limited seed-dispersal range of this species, thereby promoting coexistence with other species.     

The shape of things eaten: the functional response of herbivores foraging adaptively

We studied reproductive and somatic investments in >700 female Richardson's ground squirrels ( Spermophilus richardsonii ) of known age over a 14-year period to evaluate three hypotheses, restraint, senescence, and residual reproductive value, proposed to explain age-specific life history patterns in iteroparous vertebrates. We found that reproductive investment, measured as litter mass at first emergence from the natal nest, did not differ among age classes. Although yearling female Richardson's ground squirrels made a greater somatic investment during reproduction than older females, they produced similar numbers and mass of offspring as older females. Reproductive investment did not decline with age, though active season somatic investment was lowest in the oldest females. Somatic investment during reproduction was highest in yearlings. This combination of age-related changes in somatic investment unaccompanied by changes in reproductive investment was not well explained by any of the hypotheses examined, though the senescence hypothesis best explained the combination of declining somatic investment and declining survival of the oldest females. Our results supported the ideas that reproductive and somatic senescence evolve independently, and that somatic senescence may be more common in relatively smaller species.