Simulation study of territory size distributions in subterranean termites

In this study, on the basis of empirical data, we have simulated the foraging tunnel patterns of two subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), using a two-dimensional model. We have defined a territory as a convex polygon containing a tunnel pattern and explored the effects of competition among termite territory colonies on the territory size distribution in the steady state that was attained after a sufficient simulation time. In the model, territorial competition was characterized by a blocking probability P_block that quantitatively describes the ease with which a tunnel stops its advancement when it meets another tunnel; higher P_block values imply easier termination. In the beginning of the simulation run, N=10, 20,…,100 territory seeds, representing the founding pair, were randomly distributed on a square area. When the territory density was less (N=20), the differences in the territory size distributions for different P_block values were small because the territories had sufficient space to grow without strong competitions. Further, when the territory density was higher (N>20), the territory sizes increased in accordance with the combinational effect of P_block and N. In order to understand these effects better, we introduced an interference coefficient γ. We mathematically derived γ as a function of P_block and N: γ(N,P_block)=a(N)P_block/(P_block+b(N)). a(N) and b(N) are functions of N/(N+c) and d/(N+c), respectively, and c and d are constants characterizing territorial competition. The γ function is applicable to characterize the territoriality of various species and increases with both the P_block values and N; higher γ values imply higher limitations of the network growth. We used the γ function, fitted the simulation results, and determined the c and d values. In addition, we have briefly discussed the predictability of the present model by comparing it with our previous lattice model that had been used to explain the territory size distributions of mangrove termites on the Atlantic coast of Panama.     

Home range,activity and sociality of a top predator,the dingo: a test of the Resource Dispersion Hypothesis

The idea that groups of individuals may develop around resource patches led to the formulation of the Resource Dispersion Hypothesis (RDH). We tested the predictions of the RDH, within a quasi‐experimental framework, using Australia’s largest terrestrial predator, the dingo Canis lupus dingo. Average dingo group sizes were higher in areas with abundant focal food sources around two mine sites compared with those in more distant areas. This supports the notion that resource richness favours larger group size, consistent with the RDH. Irrespective of season or sex, average home range estimates and daily activity for dingoes around the mine sites were significantly less than for dingoes that lived well away. Assuming that a territory is the defended part of the home range and that territory size is correlated with home range size, consistent with the RDH, the spatial dispersion of food patches therefore determined territory size for dingoes in our study. However, although sample size was small, some dingoes that accessed the supplementary food resource at the mines also spent a large proportion of their time away, suggesting a breakdown of territorial defence around the focal food resource. This, in combination with the large variation in home range size among dingoes that accessed the same supplementary food resource, limits the predictive capabilities of the RDH for this species. We hypothesize that constraints on exclusive home range occupancy will arise if a surfeit of food resources (in excess of requirements for homeostasis) is available in a small area, and that this will have further effects on access to mates and social structure. We present a conceptual model of facultative territorial defence where focal resources are available to demonstrate our findings.     

Ecological correlates to social structure in two lemur species in Madagascar

In this study, I tested two hypotheses regarding the relationship of ecological variables (size, density, and distribution of patches) and infant developmental patterns to lemur social structure using two prosimian primates in Ranomafana, Madagascar: the rufous lemur (Eulemur fulvus rufus) and the red-bellied lemur (Eulemur rubriventer). Three predictions regarding the general effects of patch size and subgroup size on lemur feeding rates were supported: (1) Rufous lemurs used large patches; red-bellied lemurs used smaller patches; (2) larger subgroups of rufous lemurs used larger patches; and (3) rufous lemur feeding rates decreased significantly with increases in subgroup size and patch size, whereas size and patch size had no significant effect on red-bellied lemur feeding rates. However, food item size (fruit) had a more significant effect on rufous and red-bellied lemur feeding rates than either patch size or subgroup size. When similar-sized fruits were compared, rufous lemur feeding rates on small fruit were most affected by patch size, yet feeding rates on medium-sized fruit were most affected by subgroup size. Neither lemur species used patches in consistent ways seasonally. During periods of food abundance, rufous lemurs used many small, common, and clumped patches. In food scarcity periods, they used fewer, larger, rarer, and less clumped patches; groups migrated when food became most scarce. Red-bellied lemurs also used patches in variable ways, but these patterns were not linked with food availability. Finally, infant development patterns differed between lemur species; red-bellied lemur males cared for offspring and infants reached developmental landmarks faster than rufous lemur infants. Therefore, red-bellied lemur group size may be constrained by the need for additional infant care by other group members. In contrast, rufous lemur group size may be constrained by patch availability during the most critical period of food scarcity. © 1996 Wiley-Liss, Inc.     

Niche dimensions of New England cottontails in relation to habitat patch size

We examined physical condition, niche dimensions, and survival of New England cottontails (Sylvilagus transitionalis) that occupied 21 habitat patches of different sizes during winter. Rabbits on small patches (2.5 ha) were predominantly males, and both sexes had lower body mass than individuals on large patches (5.0 ha). Niche indices (, where ranges from 0 to 1. and values approaching 1 indicate generalized resource use) of habitat use revealed that rabbits on small patches used a greater variety of microhabitats (based on understory stem density: _s, and proximity to cover: _c) than rabbits occupying large patches (_s=0.65, _c=0.66). Rabbits on small patches also consumed low quality forage more often and fed at sites farther from escape cover than rabbits on large patches. There were no significant correlations between rabbit densities and niche dimensions. Niche expansion was not a result of compertitive release or relaxation of predator pressure. Rabbits on small patches apparently modified their niche dimensions in response to resource limitations. This response included occupying sites with limited understory cover that apparently resulted in rabbits on small patches having a lower survival rate (0.35) than rabbits on large patches (0.69) during a 10-week monitoring period. Skewed sex ratios and low survival rates among rabbits on small patches suggest that these habitats act as sinks to dispersing, juveniles from large (source) patches. As a result, local populations of New England cottontails may become vulnerable to extinction if larte patches of habitat are not maintained.     

Ecological constraints on group size in three species of neotropical primates

The foraging strategies and association patterns of 3 species of primates (Ateles geoffroyi, Alouatta palliata, Cebus capucinus) were studied over a 5-year period. The objective of the study was to provide a quantitative test of the hypothesis that the size, density and distribution of food resources influence the size of animal groups. In examining the assumptions of this hypothesis, it was shown that these primates used resources that occurred in patches, depleted the patches through their use, and that membership in large subgroups was associated with increased travel costs. The howler and spider monkey groups formed subgroups, the size of which could be predicted from the size, density and distribution of their plant food resources. When resources were clumped and at a low density, both the howler and spider monkeys were found in small subgroups, whereas when patches were uniformly distributed and at high density they formed larger subgroups. Capuchin monkeys, in contrast, did not respond to changes in these ecological variables by forming subgroups or changing the cohesion of their group.     

Similarity in occupancy of different-sized forest patches by small mammals on clearcuts: conservation implications for red-backed voles and small mustelids

Many mammalian species decline on forest sites that are harvested by clearcutting because of a loss of food, cover, and other components of stand structure. Small mustelids are impacted negatively as is the southern red-backed vole (Myodes gapperi), a principal prey species, that disappears from clearcuts within a year of harvest. These effects may be potentially ameliorated by aggregated retention harvests that leave unlogged patches on clearcuts. We tested three hypotheses (H) that (H₁) abundance, reproduction, and survival of M. gapperi populations, (H₂) total abundance, species richness, and diversity of the forest-floor small mammal community, and (H₃) the presence of small mustelids would be greater in large than small patches of retention forest on new clearcuts. We measured demographic responses of M. gapperi, total small mammals, and the presence of small mustelids (American marten, Martes americana, and small weasels (Mustela spp.)) from 2014 to 2016 in replicated treatments of four sizes (ha) of retention patches (means of 0.53, 1.50, 4.13, and 18.73) near Elkhart in south-central British Columbia, Canada. Mean abundance, reproduction, and survival attributes of M. gapperi were similar among treatment sites over the 3-year study. Overall mean abundance ranged from 3.5 to 5.3 voles per line in patches while this microtine was extirpated on clearcut sites (i.e., no forest patches). The similarity in population dynamics among the various forest patches across a gradient of increasing patch size of 4.5 to 35.3 times did not support H₁. Mean abundance, species richness, and diversity of total forest-floor small mammals were similar among treatment sites, and hence did not support H₂. Although not formally significant, mean species diversity did show a consistent increase from the largest (0.82) to the smallest (1.11) patch size, owing primarily to the presence of several generalist species such as Neotamias amoenus, Microtus, and Sorex in nearby early successional habitat. Small mustelids were present at similar levels among patch sizes, presumably in response to abundance of small mammal prey, and hence did not support H₃. Although our results were relatively short-term, the detailed assessment of population dynamics of M. gapperi indicated that habitat quality was sufficient to maintain this species regardless of patch sizes, ranging from 0.3 to 20.0 ha. Similarly, the total forest-floor small mammal community and presence of small mustelids also followed this pattern. All sizes of forest patches have conservation value and will help to maintain abundance and diversity of forest mammals, both predator and prey species, on clearcuts. Longer-term studies (e.g., at 5- to 10-year intervals) are essential to determine if our results are sustainable in augmenting forest restoration.

     

Seasonal diet and prey selection of black‐backed jackals on a small‐livestock farm in South Africa

The extent to which black‐backed jackals (Canis mesomelas) selectively consume domestic sheep (Ovis aries) compared to wild prey is unknown. Using faecal analysis and prey surveys, we determined the seasonal diet and prey selection of jackals on a small‐livestock farm in South Africa. Sheep comprised 25–48% of the biomass consumed by jackals across seasons, and consumption peaked during the lambing seasons, indicating sheep often were the main food resource for jackals. Another main food resource was wild ungulates <50 kg, primarily springbok (Antidorcas marsupialis) and steenbok (Raphicerus campestris), which comprised 8–47% of the biomass consumed. Other important food items were mammals 1–3 kg (4–16%), which included hares (Lepus spp.) and springhares (Pedetes capensis), and small rodents (10–14%). Compared to the biomass available, jackals selectively consumed mammals 1–3 kg over sheep across all seasons, whereas wild ungulates <50 kg were selectively consumed over sheep in most seasons. Our results showed that jackals selectively consumed different food items throughout the year and that wild prey were consistently selected over sheep.     

Defense of Food Supply by Eusocial Colonies

Overdispersion of colonies exists in many eusocial insects.Overdispersion can be generated by direct attack on coloniesor founders, by defense of space, by defense of food resourcesbeing harvested, or by exploitative competition. When directcompetitive interactions lead to colony overdispersion, territorialityis said to occur. Whereas solitary territory holders typicallydefend space, most eusocial colonies defend resource patchesrather than space per se. Also unlike solitary territory holders,colonies with forager communication can simultaneously defendseveral spatially separated food patches. A model explores optimalnumbers of scouts (discoverers of patches) and recruits (followers)needed to maximize net rate of energy intake by the colony.Territorial costs are added to the model by requiring a higherinvestment of foragers per unit resource collected. Accordingto the model, optimal colony size and percentage scouts aremore sensitive to changes in patch size than in patch density.If patch defense is required for resource control, a declineoccurs in optimal percentage of scouts; the decline is greatestfor small colonies. Colonies that must defend patches in orderto harvest from them suffer a loss in net energy intake; theloss is greatest for small colonies. It is predicted that amongeusocial insects, those with territorial defense of resourcesshould preferentially visit large patches and have comparativelylarge colony sizes and relatively few scouts. Ways of testingthese predictions are discussed.     

Group foraging in wild brown hares: effects of resource distribution and social status

Wild brown hares (Lepus europaeus), though normally comparatively solitary, have the capacity to adjust their behaviour such that they can benefit when foraging in groups. They are able to allocate more time to feeding and have an increased corporate vigilance as group size increases. However, these benefits are conditional upon the food distribution. When food is spaced, all individuals benefit. When it is clumped into a small defendable patch, dominant hares attempt to monopolize the resource. They can successfully exclude subordinates when group size is small but, as group size increases, they must devote more time to defending the patch. Therefore, dominants spend less time feeding with increasing group size, while subordinates spend more, since they have more opportunity to feed while the dominant hare is off chasing other individuals. As a consequence, when more than two hares are present, all individuals do less well when food is clumped than when it is spaced.     

Morphological and genetic divergence in Swedish postglacial stickleback (Pungitius pungitius) populations

Background

An important objective of evolutionary biology is to understand the processes that govern phenotypic variation in natural populations. We assessed patterns of morphological and genetic divergence among coastal and inland lake populations of nine-spined stickleback in northern Sweden. Coastal populations are either from the Baltic coast (n = 5) or from nearby coastal lakes (n = 3) that became isolated from the Baltic Sea (< 100 years before present, ybp). Inland populations are from freshwater lakes that became isolated from the Baltic approximately 10,000 ybp; either single species lakes without predators (n = 5), or lakes with a recent history of predation (n = 5) from stocking of salmonid predators (~50 ybp).

Results

Coastal populations showed little variation in 11 morphological traits and had longer spines per unit of body length than inland populations. Inland populations were larger, on average, and showed greater morphological variation than coastal populations. A principal component analysis (PCA) across all populations revealed two major morphological axes related to spine length (PC1, 47.7% variation) and body size (PC2, 32.9% variation). Analysis of PCA scores showed marked similarity in coastal (Baltic coast and coastal lake) populations. PCA scores indicate that inland populations with predators have higher within-group variance in spine length and lower within-group variance in body size than inland populations without predators. Estimates of within-group P _ST (a proxy for Q _ST) from PCA scores are similar to estimates of F _ST for coastal lake populations but P _ST > F _ST for Baltic coast populations. P _ST > F _ST for PC1 and PC2 for inland predator and inland no predator populations, with the exception that P _ST < F _ST for body size in inland populations lacking predators.

Conclusions

Baltic coast and coastal lake populations show little morphological and genetic variation within and between groups suggesting that these populations experience similar ecological conditions and that time since isolation of coastal lakes has been insufficient to demonstrate divergent morphology in coastal lake populations. Inland populations, on the other hand, showed much greater morphological and genetic variation characteristic of long periods of isolation. Inland populations from lakes without predators generally have larger body size, and smaller spine length relative to body size, suggesting systematic reduction in spine length. In contrast, inland populations with predators exhibit a wider range of spine lengths relative to body size suggesting that this trait is responding to local predation pressure differently among these populations. Taken together the results suggest that predation plays a role in shaping morphological variation among isolated inland populations. However, we cannot rule out that a causal relationship between predation versus other genetic and environmental influences on phenotypic variation not measured in this study exists, and this warrants further investigation.     

Effects of herbivory by chrysomelid beetles on the growth and survival ofRumex plants

The effects of herbivory by the guild of chrysomelid beetles on the growth and survival ofRumex plants were examined in relation to the distribution and size of the plants. Gastrophysa atrocyanea never appeared on solitary plants whereasMantula clavareaui showed even utilization of solitary and clumped plants.Galerucella vittaticollis utilized large solitary plants most frequently. In patches of the host plants, the frequency of withering of the aerial parts was higher on small plants. The regrowth rate was higher when the aerial parts withered in spring than in summer. In patches of the host plants, the regrowth rate was higher on small plants. On the other hand, it was lower on small solitary plants than on large solitary plants and small plants in patches. In large plants, no difference in survival rate was recognized between solitary and clumped plants, because both the frequency of withering of the aerial parts and the regrowth rate were lower in clumped than solitary plants. The high vigor against intense herbivory by the chrysomelid beetles brought on the delay in the phenology ofRumex plants. This shift permits in parts the existence ofG. vittaticollis in mid summer. The temporal and spatial interactions between herbivore guild and the host plants were discussed.     

Eelgrass patch size and proximity to the patch edge affect predation risk of recently settled age 0 cod (Gadus)

Postsettled age 0 Atlantic cod (Gadus morhua) seek refuge from predation in eelgrass (Zostera marina) habitat within shallow, coastal nurseries. Laboratory and field experiments have demonstrated that predation risk on small fish is reduced in habitats of greater structure compared to less complex or barren environs. To determine if predation risk is linked to the areal extent of eelgrass coverage, we tested the hypothesis that predation risk of age 0 cod decreases with increasing eelgrass patch size. Predation on tethered age 0 cod (G. morhua and G. ogac) was quantified in eelgrass patches (1-80 m²) at three sites in northeastern Newfoundland, Canada, during September and October 1999 and 2000. Based on evidence of edge effects in terrestrial landscapes, we also tested the hypothesis that predation is elevated at ecotones separating eelgrass from adjacent barren mud substrate. We examined predation at the edge (i.e., 0 m) and both 5 and 10 m from this edge into and away from eelgrass cover along an 18 m long barren mud-gravel and eelgrass boundary, at two sites. Logistic regression analysis showed that the risk of predation, as measured by the odds ratio, increased with area over a small range of patch sizes (1-35 m² in 1999). When the study was extended to a wider range of patch sizes (1-80 m²) in 2000, a parabolic relationship emerged, with patches on the order of 25 m² providing the least safety and the largest patches (80 m²) providing the most safety. Predation on tethered cod was highest at the edge of eelgrass patches, compared with barren and eelgrass locations; predation generally decreased with distance from the eelgrass boundary. Our results are consistent with the hypothesis that predators are drawn to large patches of eelgrass because of increased prey numbers, that predators increase their success by searching edges, and that this results in greatest predation risk to prey in isolated patches of intermediate size.     

Food patch structure and plant resource partitioning in interspecific associations of amazonian tamarins

ávila-Pires’ saddle-back tamarins (Saguinus fuscicollis avilapiresi) and red-cap moustached tamarins (S. mystax pileatus), coexisting in highly stable mixed-species groups, overlapped considerably in their use of plant food resources at an Amazonian terra firme forest site. Overlap between food types consumed by the two species was particularly high during periods of lowest fruit availability, when they resorted to a common food supply, primarily the pod exudates of two emergent species of legume trees (Parkia nitida andParkia pendula) and nectar ofSymphonia globulifera. Within-group interspecific competition did not covary with independent measures of resource availability, contrary to predictions based on resource partitioning models. A greater number of both saddle-back and moustached tamarins were able to feed for longer patch residence periods within larger and more productive food patches, whereas small and clumped patches could be monopolized by the socially and numerically dominant moustached tamarins to the physical exclusion of the smaller-bodied saddle-back tamarins. Overall rates of interspecific aggression were extremely low, however, partly because patches that could be monopolized contributed with a minor proportion of either species’ diet. Saddle-backs foraged at lower levels in the understory and encountered smaller food patches more often, whereas moustached tamarins foraged higher and encountered more larger patches in the middle canopy. Although the two species led one another to differently-sized patches, moustached tamarins initiated most feeding bouts and encountered significantly larger and more productive patches that tended to accommodate the entire mixed-species group. Disadvantages of exploitative and interference feeding competition over plant resources, and advantages of shared knowledge of food patches, are but one component of the overall cost-benefit relationship of interspecific associations in tamarins.     

Host location success of root-feeding nematodes in patches that differ in size and quality: A belowground release-recapture experiment

Resource patch size and patch nutritional quality are both important factors influencing local densities of herbivores. The responses of herbivores to resource patch size have been mostly studied in aboveground plant–insect interactions, whereas belowground organisms have received little attention. We studied responses of different root-feeding nematode species associated with marram grass (Ammophila arenaria (L.) Link) to resource patch size and quality. Different nematode species were released in experimental mesocosms filled with dune sand in which we established marram grass patches of varying sizes. Half of the patches of small, medium and large size were fertilized to test if immigration probabilities of nematodes depended on patch quality. We tested the hypotheses that (1) nematodes should aggregate on larger patches and (2) colonization of patches would also depend on patch nutritional quality, with higher nematode recapture rates expected in fertilized patches. Two species (Helicotylenchus pseudorobustus, Hemicycliophora thornei) of the five released species were recaptured in the experiment. The fraction of nematodes immigrating into the rhizosphere of a plant patch increased with patch size (i.e. root biomass), which was in line with predictions of the Resource Concentration Hypothesis. When fractions were recalculated to represent recapture rates per liter of soil, recapture rates of nematodes did not differ among patch sizes, indicating that the increase in recapture rates was directly proportional to the increase in patch size. This suggests that the process through which nematodes located patches was not distinguishable from a random process where entering patches is based on random encounters with patch boundaries. In contrast to our expectation, fertilization had a strong negative effect on patch responses of both nematode species. Our study represents an approach that may be used to explore whether belowground biota behave in similar ways as aboveground biota, in order to determine how perceived differences in environments affect ecological interactions.     

Observations on variation in skull size of three mammals in Israel during the 20th century

Among mammals, food availability, especially during the growth period, is a key predictor in determining final body size, and improved nutrition may lead to an increase in their body size. In Israel during the last century food availability for animals commensal with humans increased greatly, due to a 16-fold increase in the human population and the accompanying changes, such as a 135-fold increase in the area of irrigated agriculture and the availability of large quantities of organic garbage.Using museum material, we studied temporal changes in skull size of a sample of 89 red foxes (Vulpes vulpes Linnaeus, 1758), 108 golden jackals (Canis aureus Linnaeus, 1758) and 117 Cape hares (Lepus capensis Linnaeus, 1758) collected during the 20th century. Four measurements (condylobasal length, zygomatic breadth, the length of the upper cheek teeth row and the length of the mandible) were taken for each skull, and principal component analysis was used to combine the measurements into principal components.We found that skull size of the red fox increased significantly during the 20th century, possibly due to improved food availability from man-made resources such as agricultural produce and garbage. No temporal trend in body size was detected for the jackal and hare. These differences are discussed.     

Environmental complexity and group size: Immediate effects on use of space by domestic fowl

Current housing conditions for domestic fowl (Gallus gallus domesticus) offer little in the way of environmental features biologically relevant to the birds. More specifically there is a notable absence of protective cover, a fundamental element that influences how domestic fowl use space. The availability of cover could be more relevant to small, as opposed to larger groups, because large groups offer an individual natural protection. In this experiment we investigated the immediate effects of cover panels designed to increase environmental complexity (EC) and compared their effects across three group sizes (n = 8) of five (GS₅), 10 (GS₁₀), or 20 (GS₂₀), broilers per group. Birds were tested under two different scenarios representing increasing EC, once with one long panel (single) once with four staggered small panels (quad) and once in an empty control arena (void). Each test lasted for 1 h. Core areas, or activity centers, were not affected by EC. EC had the greatest impact on the inter-individual distances of birds in smaller groups. Minimum and nearest neighbor distances in GS₅ increased significantly with EC, whereas those in the GS₁₀ and GS₂₀ were not different across the EC treatments. Because GS were housed together in a home pen and moved from this common home pen into testing arenas, significant differences in minimum, maximum, and nearest neighbor inter-individual distances suggest that birds adjusted their use of space in response to immediate changes in group size and EC. Overall we found a significant impact of EC on the spacing behavior of domestic fowl, however the effects were not equal for all group sizes. As predicted, smaller groups were more affected by environmental features, and thus may experience the greatest benefit from increased EC.     

Territory Characteristics among Three Neighboring Chimpanzee Communities in the Taï National Park,Côte d'Ivoire

We studied territory characteristics among three neighboring chimpanzee communities in the Taï National Park, Côte d'Ivoire, and compared them with other chimpanzee populations. We characterized territories and ranging patterns by analyzing six variables:, (1) territory size, (2) overlap zone, (3) territory utilization, (4) core area, (5) territory shift, and (6) travel distance. Data collection covered a period of 10 mo, during which we simultaneously sampled the local positions of mostly large parties, including males in each community, in 30-min intervals. In Taï, chimpanzees used territories in a clumped way, with small central core areas being used preferentially over large peripheral areas. Although overlap zones between study communities mainly represented infrequently visited peripheral areas, overlap zones with all neighboring communities also included intensively used central areas. Territory utilization was not strongly seasonal, with no major shift of activity center or shift of areas used over consecutive months. However, we observed shorter daily travel distances in times of low food availability. Territory sizes of Taï chimpanzees tended to be larger than territories in other chimpanzee communities, presumably because high food availability allows for economical defense of territorial borders and time investment in territorial activities. Therefore we suggest, that use of territory in Taï chimpanzees is strongly influenced by intercommunity relations. To understand differences in territory characteristics between various populations, it is of major importance to consider not only the intracommunity but also the intercommunity context.     

Attraction to Carbon Dioxide from Feeding Resources and Conspecific Neighbours in Larvae of the Rhinoceros Beetle Trypoxylus dichotomus

Saprophagous (feeding on decaying matter) insects often use carbon dioxide (CO₂) as a cue for finding food. Humus-feeding larvae of the giant rhinoceros beetle Trypoxylus dichotomus exhibit a clumped distribution in natural microhabitats, but the mechanisms driving the distribution were unknown. Herein, I examined whether larvae use CO₂ as a cue for fermented humus and aggregate in the vicinity of the food. I found that (i) larvae of T. dichotomus are strongly attracted to CO₂, (ii) larvae orient toward highly fermented humus when given a choice between highly and poorly fermented humus, (iii) the highly fermented humus emits more CO₂ than the poorly fermented humus, and (iv) larvae grow larger when fed highly fermented humus rather than poorly fermented humus. The clumped distribution of larvae is probably formed along the concentration gradient of CO₂ induced by heterogeneity of fermented organic materials in soil. My laboratory experiments also revealed that larvae are chemically attracted to each other. Moreover, CO₂ concentrations in soil were increased by the larval respiration, and small amounts of CO₂ (much less than emitted during respiration by a single larva) were sufficient for larval attraction. These results suggest that not only response to fermented food resources, but also respiratory CO₂ from conspecifics may lead to aggregation. Enhanced densities resulted in reduced weight gain under experimental conditions. However, exploiting a high-value resource at enhanced densities still led to greater body weight compared to individually exploiting a low-value resource. This demonstrates the adaptive value of the response to CO₂ sources in this species.     

Influence of spatial distribution and size of clones on the realized outcrossing rate of the marsh cinquefoil (Comarum palustre)

Background and Aims

Clonal growth is a common feature in flowering plants. As clone size increases, the selfing rate in self-compatible species is likely to increase due to more frequent geitono-pollination events (i.e. pollination among flowers within the same genet). This study investigated the breeding system of the marsh cinquefoil (Comarum palustre) and assessed spatial distribution of clones, clone size and architecture, and their effects on realized outcrossing rates. In addition, pollen dispersal was investigated in two patchy populations.

Methods

The species'' breeding system was investigated under controlled conditions through hand pollinations (self- vs. cross-pollination). Using microsatellite markers, an assessment was made of the realized outcrossing rates and the genetic diversity in four natural populations, the clonal structure in two populations within five 15 × 15 m sampling plots following 0·5 × 0·5 m grids, and the pollen dispersal through paternity assignment tests in those two populations.

Key Results Comarum palustre

is a self-compatible species but only presents a low rate of spontaneous self-pollination. The occurrence of inbreeding depression was not detected at the seed set stage (δ_SS = 0·04). Clones were spatially clumped (A_C = 0·60–0·80), with intermediate to no intermingling of the ramets (D_C = 0·40–1·00). Genet size ranged from one to 171 ramets. Patchy populations had low outcrossing rates (t_m = 0·33–0·46). Large clones showed lower outcrossing rates than small clones. Pollen dispersal mainly occurred within patches as only 1–7 % of the pollination events occurred between patches of >25 m separation. Seedling recruitment events were detected.

Conclusions

Genet size together with distances between patches, through increasing geitono-pollination events, appeared to be important factors influencing realized outcrossing rates. The study also revealed seed flow allowing seedling recruitment, which may contribute to increasing the number of new patches, and potentially further enhance gene flow within populations.