The diet of the South Georgia shag Phalacrocorax georgianus at South Orkney Islands in five consecutive years

The diet of the South Georgia shag Phalacrocorax georgianus at Laurie Island, South Orkney Islands, was studied by the analysis of 420 pellets (regurgitated casts) collected from the 1995 to 1999 breeding seasons. Demersal-benthic fish were by far the main prey, followed by molluscs (mainly octopods and bivalves) and polychaetes. Harpagifer antarcticus (in 1995, 1998, 1999) and Lepidonotothen nudifrons (1996, 1997) were the most frequent prey, followed by Gobionotothen gibberifrons or Trematomus newnesi. Harpagifer antarcticus, followed by L. nudifrons or T. newnesi, was the most numerous prey in all of the seasons and predominated in mass in 1995 and 1996, followed by Notothenia coriiceps and L. nudifrons. In 1997 and 1999, G. gibberifrons and N. coriiceps were the species that most contributed to the diet whereas N. coriiceps and H. antarcticus contributed most in 1998. Our results differ from those reported for the South Orkney Islands in previous studies. These differences could be due to the use of different diet-analysis methods and to shags-related and/or fisheries-related changes in the food availability around the colonies. These alternative explanations are analysed and discussed.     

On spatiotemporal patchiness and the coexistence of five species of Chronogaster (Nematoda: Chronogasteridae) in a riparian wetland

Spatiotemporal patchiness in the soil environment is thought to be crucial for the maintenance of soil biodiversity. It provides diverse microhabitats (allowing resource partitioning), and presents these in a complex mosaic, such that competitors may be spatially and temporally separated (promoting patch dynamics). The objective of our study was to assess the importance of patch dynamics for the maintenance of landscape-level nematode diversity. The spatiotemporal aggregation patterns in populations of five species of the bacterivorous genus Chronogaster were analyzed for a 0.7-ha riparian wetland, during four seasons, using geostatistical methods (spatiotemporal variograms, cross-correlograms, and log-normal kriging). We found that for the three most abundant species, aggregation was significant over distances of 13-39 m, with intraspecific aggregation stronger than interspecific aggregation. In addition, species patterns appeared to be temporally dynamic: local population declines alternated with local blooms at different sites and seasons. One species was consistently present at the same few sites, but the other species showed gradual temporal decreases and increases at different locations in the wetland. Combining nematode patterns with information on soil resource distributions and Chronogaster ecology, indicated that both soil resource patchiness and repeated, but largely unpredictable, disturbances caused by local soil moisture fluctuations could promote landscape-level Chronogaster diversity by providing ample 'probability refuges.' Local species populations, reduced by competition, predation and drought, could recolonize patches either through the awakening of local dormant 'seed populations,' or through limited passive dispersal by wind, water, and phoresis. We suggest that the spatiotemporal Chronogaster data provide preliminary evidence for the importance of patch dynamics in maintaining soil nematode diversity.     

Population trends, breeding success and diet composition of gentoo Pygoscelis papua, magellanic Spheniscus magellanicus and rockhopper Eudyptes chrysocome penguins in the Falkland Islands. A review

Data on population size, breeding success and diet composition of gentoo (Pygoscelis papua), magellanic (Spheniscus magellanicus) and rockhopper (Eudyptes chrysocome) penguins, collected as part of the Falkland Island Seabird Monitoring Programme from 1986/1987 to 1998/1999, were analysed with regard to spatial and temporal variation, as well as potential interaction with local commercial fisheries. No significant population trends were detectable, mainly because of the short time-series and large spatial and inter-annual variation in the number of breeding pairs in the colonies monitored. However, the breeding success of all three penguin species has improved slightly over the last few years, indicating a potential for increasing populations in the near future. During the breeding season, all three penguin species preyed opportunistically on a mixture of fish, squid and crustaceans. Diet composition too showed a high degree of spatial and temporal variation. However, in all three penguin species studied, squid gradually disappeared from the diet over successive years, to be replaced by fish. Coincidentally, the commercial catches of the squid species Loligo gahi in Falkland Islands waters decreased and the by-catch of nototheniid fish increased. All three penguin species compete directly with the commercial fishing fleet for L. gahi; however, there may also be competition for Patagonian toothfish (Dissostichus eleginoides), hake (Merluccius sp.) and southern blue whiting (Micromesistius australis), because juveniles of these species were found regularly in penguin diets.     

Restricted dispersal in a long-distance migrant bird with patchy distribution,the great reed warbler

In patchily distributed species dispersal connects local populations into metapopulations. Reliable quantifications of dispersal are therefore crucial to understanding the population dynamics and genetic structure of such metapopulation systems. The great reed warbler (Acrocephalus arundinaceus) inhabits eutrophic lakes and has a patchy breeding distribution. In this study we investigated the dispersal pattern of the great reed warbler based on an extensive capture-recapture effort covering a large census area (22,500 km²). At two adjacent breeding sites (10 km apart) in southern Central Sweden, the "main study area", we ringed the majority of adult and nestling great reed warblers between 1992 and 1999. In 1998 and 1999, we opportunistically searched for territorial males at the majority of the Swedish breeding sites, and were able to examine about 56% of all males in the region. Analyses of recaptured males demonstrated that philopatry predominated. Sixty-nine percent of the recruiting nestlings returned to breed in the main study area (their natal area), and 92% of the resighted adults were found at the same breeding locality in both study years. Breeding dispersal was significantly more restricted than natal dispersal. Additional data on natal and breeding dispersal within the main study area in 1992-1999 suggested that females were as philopatric as males. The overall high level of philopatry, with only occasional longer dispersal distances documented, yielded a root-mean-square dispersal distance of 33 km per generation. High philopatry, short dispersal distances and similar dispersal patterns of male and female great reed warblers contrast the findings among birds in general, but conform to data of species having patchy breeding habitat and isolated populations. Restricted dispersal suggests limited gene flow even among several Swedish populations, which is in line with some previous findings of the population ecology of the great reed warbler: (1) structured mtDNA lineages among European populations; (2) small-scale population differences in song patterns; and (3) low genetic variation and occurrence of inbreeding depression in our main study population.     

The role of introduced mosquitofish (Gambusia holbrooki) in excluding the native green and golden bell frog (Litoria aurea) from original habitats in south-eastern Australia

The introduction of fish has decimated many amphibian populations through increased predation, primarily on their larvae. Some amphibian species now occupy marginal habitats as a response to the presence of introduced fish predators. Such habitats may include ephemeral water bodies where fish do not usually occur, although breeding in these suboptimal environments may incur some cost to a species if its larvae are not adapted to develop under these conditions. We investigated this scenario of amphibian decline using the endangered green and golden bell frog (Litoria aurea) and the introduced mosquitofish (Gambusia holbrooki) in a factorial experiment to determine the responses of tadpoles to declining water levels and the introduced predator. Tadpoles metamorphosed asynchronously but did not accelerate development in declining water or when housed with mosquitofish. Mass at metamorphosis was 30% less in declining water. Mass increased with time to metamorphosis in constant water-level treatments, but decreased in declining water. Tadpoles did not respond to mosquitofish and were therefore assumed to be naive to this predator. These results suggest that ephemeral habitats may be suboptimal for breeding, and tadpoles appear better suited to develop in permanent water bodies free of introduced fish. Intra-clutch variability in larval development (i.e. bet-hedging) may allow L. aurea to cope with unpredictable pond duration, whereby even permanent water bodies may occasionally dry out. The responses observed in L. aurea suggest that introduced fish may have reduced the suitability of permanent water bodies as breeding sites for other pond-breeding amphibian species. The use of less favourable ephemeral habitats as breeding sites may be responsible for some of the declines reported in amphibians since the 1970s.     

Monoxenic maintenance and reproduction of root-knot nematode (Meloidogyne hapla) on multiple-species in vitro root culture systems

The ability of tomato root tips transformed with Agrobacterium rhizogenes and non-transformed onion and dandelion root tips to regenerate and provide suitable monoxenic hosts for the maintenance of root-knot nematode (Meloidogyne hapla) was investigated. Populations of M. hapla were successfully established on all root culture systems examined, but the onion root culture was overall the most effective method for long-term maintenance and reproduction of M. hapla. The use of a pre-induction medium containing the hormone !-naphthaleneacetic acid was necessary for the production of onion root culture systems but was not required for the establishment of tomato or dandelion root cultures. Differences in nematode reproduction were observed on tomato when multiple populations of M. hapla were used for inoculations.     

Causes and consequences of small population size for a specialist parasitoid wasp

The parasitoid wasp Cotesia melitaearum lives in extremely small extinction-prone populations in the Åland islands of southwest Finland. Intensive observational data from two generations, a laboratory competition experiment, and 8 years of survey data were used to measure the causes, extent and consequences of small population size for this parasitoid. In the spring generations of 1999 and of 2000 we observed 21 out of 23 and 26 populations respectively, ranging in size from 2 to 103 parasitoid cocoons. Within these populations the fraction of individuals surviving to adulthood decreased with increasing parasitoid population size. The largest source of mortality was predation (44%) followed by parasitism (20%) and unknown causes (10%). In the field about 30% of the host butterfly larvae are parasitized by a competing parasitoid, Hyposoter horticola. A laboratory competition experiment showed that C. melitaearum eggs died when laid in post-diapause host larvae occupied by H. horticola. Consequently one-third of the progeny of the over-wintering generation of C. melitaearum from the field die as a result of larval competition. The survey of host and parasitoid population dynamics over 8 years showed that extinction of local host butterfly populations occupied by the parasitoid was not associated with current parasitoid population size. Over the same period small parasitoid populations were more likely to become extinct than large populations. However, parasitoid population size was not related to parasitoid extinction when the host also became extinct. These data suggest that the parasitoid populations are kept small through the action of natural enemies and competitors, some of which are density dependent. Local populations are so small that they become extinct frequently and rarely measurably affect the population dynamics of their host. It is likely that this parasitoid persists in Åland because of the spatial asynchrony of local population dynamics.     

Plant polyploidy and host expansion in an insect herbivore

Polyploidization has played an essential role in the diversification of seed plants and often has profound effects on plant physiology and morphology. Yet, little is known about how plant polyploidization has shaped the ecology and evolution of interactions between phytophagous insects and their hosts. Polyploidization could either facilitate or impede colonization of new hosts. Greya politella (Lepidoptera: Prodoxidae) is highly specialized on plants in the genus Lithophragma (Saxifragaceae) throughout most of its geographic range. In central Idaho, some populations have shifted to the related Heuchera grossulariifolia, a plant that has repeatedly undergone autopolyploidization. Previous studies have shown that populations feeding natively on H. grossulariifolia prefer tetraploids to diploids in naturally mixed stands. We investigated whether this difference is caused by an inherent preference for tetraploids, or if the preference in present Heuchera-feeding populations has evolved over time. Moths from a strictly Lithophragma-feeding population were tested for preference of diploid or tetraploid H. grossulariifolia, using a combination of field experiments and caged choice trials. In all trials, attack rates on these non-hosts were very low, with no significant difference between ploidies. In addition, there was little evidence that females manipulated their clutch sizes when ovipositing into different plant species or ploidy levels. Hence, the local shift from Lithophragma to Heuchera in central Idaho is not due to failure of the moths to discriminate between these plant species. Furthermore, the higher attack rates on tetraploids in native H. grossulariifolia-feeding populations cannot be caused by a higher initial preference for these plants, but must instead be a result of differences in plant phenology and/or selection acting on local populations.     

Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae)

Several species of gall-forming insects specialize on big sagebrush (Artemisia tridentata), a species that shows much clinal and subspecific variation throughout its geographic range. Two of those subspecies, basin big sagebrush (A. t. ssp. tridentata) and mountain big sagebrush (A. t. ssp. vaseyana), form a narrow hybrid zone at Salt Creek, Utah. Reciprocal transplant experiments have shown that the hybrid big sagebrush at Salt Creek are more fit than either parental subspecies, but only in the hybrid zone. Do genotype and environment influence the density and distribution of galls on big sagebrush? We counted galls on parental and hybrid big sagebrush in three reciprocal transplant gardens at Salt Creek. Gardens were in each of the two parental zones and in the hybrid zone. Transplanted seedlings came from five source populations: two parental and three hybrid populations. We identified seven kinds of gall-forming flies (Rhopalomyia midges and Eutreta fruitflies) that produced identifiable galls. Densities of galls varied among the three gardens and five source populations, and there was also a significant garden by source interaction in gall density. In general, variation in gall density among gardens (i.e., environments) was much greater than the variation among source populations (i.e., genotypes). Nevertheless, significant genotype-environment interactions were observed for five of the seven kinds of galls. Overall density of galls, mostly due to Rhopalomyia ampullaria, was greatest in the high-elevation (mountain) garden and least in the low-elevation (basin) garden. To the best of our knowledge, this is the first reciprocal transplant experiment addressing herbivore richness in a hybrid zone.     

Interspecific differences in cuticular hydrocarbon profiles of Myrmica ants are sufficiently consistent to explain host specificity by Maculinea (large blue) butterflies

The chemical signatures on the cuticles of five common Myrmica ant species were analysed (49 colonies of M. rubra, M. ruginodis, M. sabuleti, M. scabrinodis and M. schencki), each ant being the specific host of one of the five threatened European species of Maculinea butterfly. The cuticular hydrocarbon profile (based on the relative abundance of each chemical) of each ant species was highly distinctive, even between the morphologically similar species M. sabuleti and M. scabrinodis. There was no significant difference in the chemical profiles of workers and larvae from any colony. Nor was there much pattern in the intraspecific variation: colonies from the same populations were significantly, but only slightly, more similar to each other than to colonies from distant populations. M. rubra showed remarkably little variation between populations sampled widely from northern Russia, Ukraine, Scotland and southern England. The data were compared with published profiles of M. rubra and two North American Myrmica species, and with a quantitative reanalysis of data for Maculinea rebeli caterpillars. We conclude that the hydrocarbon profiles of Myrmica species are sufficiently and consistently different for chemical mimicry to explain the pattern of host specificity recorded for the European Maculinea butterflies. The optimum strategy for chemical mimicry in each of the two life-styles of Maculinea larvae is discussed: we suggest that predatory species might benefit from mimicking the median profile of their model whereas the "cuckoo" species would benefit when variation between siblings encompasses a large range of the variation recorded within a local population of the model species.     

Genetic variation and a fitness tradeoff in the tolerance of gray treefrog (Hyla versicolor) tadpoles to the insecticide carbaryl

One of the major unanswered questions in the study of global amphibian declines is why only some species or populations suffer declines. A possible explanation is that species and populations vary in the genetic basis of their tolerance to environmental stress such as chemical contamination. The presence of genetic variation in tolerance to chemicals and in fitness traits of amphibians is essential for persistence of species populations through survival and successful reproduction in contaminated environments. We tested for the presence of genetic variation in the tolerance of amphibian larvae to the insecticide carbaryl using gray treefrog tadpoles (Hyla versicolor). We also assessed whether tolerance of tadpoles is negatively associated with larval performance traits directly related to adult fitness, thereby providing a test of the "cost of tolerance" hypothesis. Our results demonstrate significant variation in tolerance of tadpoles to the insecticide carbaryl within a single population of the gray treefrog, Hyla versicolor. Our half-sibship design indicates that variation among sires explains a significant amount of the variation in chemical tolerance thereby suggesting a heritability genetic basis. Our results also indicate the presence of a fitness tradeoff with tolerance to the chemical carbaryl being negatively correlated, or traded off, with survival of tadpoles reared in the field in the absence of the chemical. Knowledge of genetic tradeoffs with chemical tolerance under realistic environmental conditions will be important for predicting the rate of adaptation and potential for persistence of species. Finally, the partitioning of environmental and genetic variation in tolerance to chemicals is critical to identifying which species are most susceptible, the amount of genetic variance present, the potential for adaptation to contaminants, and the presence of fitness tradeoffs. Such information is necessary to clearly understand the persistence of populations, and ultimately, the processes leading to species declines.     

Factors affecting the breeding success of the south polar skua Catharacta maccormicki at Edmonson Point, Victoria Land, Antarctica

A south polar skua (Catharacta maccormicki) population was studied at Edmonson Point (74°20'S-165°08'E), Victoria Land, Antarctica, in 1998/1999. The local population consisted of 101 pairs, 89 of which were located within a large, loose colony associated with a rookery of about 2,000 pairs of Adélie penguin (Pygoscelis adeliae). Skua nests were clumped around penguin subcolonies. Mean skua Nearest Neighbour Distance (NND) was 21ᆣ m (n=89). NND was positively correlated with the distance from the nearest penguin subcolony. Mean laying date was 24Lj December (n=89). Mean clutch size was 1.9ǂ.2 eggs (n=89). Hatching success was 77% (n=174 eggs laid), and 20.2% of the breeding pairs successfully raised chicks to fledging. Mean number of fledged young was 0.2ǂ.4 per breeding pair (n=89), and 1 per successful pair (n=18). Main causes of breeding failure were intraspecific predation and sibling aggression. Breeding success was negatively related to distance from the nearest penguin nest and to laying date. Because of the extensive and persistent sea-ice cover, penguins represented an important source of food for the skua population.     

Primary production, light and vertical mixing in Potter Cove, a shallow bay in the maritime Antarctic

Phytoplankton photosynthesis was measured during spring-summer 1991-1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quantified by means of the root-mean square expected vertical displacement depth of cells in the water column, Z_t. The light attenuation coefficient was used as a measure of the influence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious differences between photosynthetic capacity [P*_max; averages 2.6 and 0.6 µg C (µg chlorophyll-a)^-1 h^-1] and photosynthetic efficiency {!*; 0.073 and 0.0018 µg C (µg chlorophyll-a)^-1 h^-1 [(µmol m^-2 s^-1)^-1]} values were obtained for both sites during low mixing conditions (Z_t from 10 to 20 m), while no differences were found for high mixing situations (Z_t>20 m). This suggests different photoacclimation of phytoplankton responses, induced by modifications of the light field, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P*_max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area.     

Local bumble bee decline linked to recovery of honey bees,drought effects on floral resources

Time series of abundances are critical for understanding how abiotic factors and species interactions affect population dynamics, but are rarely linked with experiments and also scarce for bee pollinators. This gap is important given concerns about declines in some bee species. I monitored honey bee (Apis mellifera) and bumble bee (Bombus spp.) foragers in coastal California from 1999, when feral A. mellifera populations were low due to Varroa destructor, until 2014. Apis mellifera increased substantially, except between 2006 and 2011, coinciding with declines in managed populations. Increases in A. mellifera strongly correlated with declines in Bombus and reduced diet overlap between them, suggesting resource competition consistent with past experimental results. Lower Bombus numbers also correlated with diminished floral resources. Declines in floral abundances were associated with drought and reduced spring rainfall. These results illustrate how competition with an introduced species may interact with climate to drive local decline of native pollinators.     

Regional and local impact on species diversity – from pattern to processes

The impact of regional factors (such as speciation or dispersal) on the species richness in local communities (S_L) has received increasing attention. A prominent method to infer the impact of regional factors is the comparison of species richness in local assemblages (S_L) with the total number of species in the region (S_R). Linear relations between S_R and S_L have been interpreted as an indication of strong regional influence and weak influence of interactions within local communities. We propose that two aspects bias the outcome of such comparisons: (1) the spatial scale of local and regional sampling, and (2) the body size of the organisms. The impact of the local area reflects the scales of ecological interactions, whereas the ratio between local and regional area reflects the inherent moment of autocorrelation. A proposed impact of body size on the relation is based on the high dispersal and high abundance of small organisms. We predict strongest linearity between S_R and S_L for large organisms, for large local areas (less important ecological interactions) and for sampling designs where the local habitat area covers a high proportion of the regional area (more important autocorrelation). We conducted a meta-analysis on 63 relations obtained from the literature. As predicted, the linearity of the relationship between S_L and S_R increased with the proportion of local to regional sampling area. In contrast, neither the body size of the organisms nor the local area itself was significantly related to the relation between S_L and S_R. This indicated that ecological interactions played a minor role in the shape of local to regional richness plots, which instead was mainly influenced by the sampling design. We found that the studies published so far were highly biased towards larger organisms and towards high similarity between the local and regional area. The proposed prevalence of linear relationships may thus be an artefact and plots of S_L to S_R are not a suitable tool with which to infer the strength of local interactions.     

Farthest north lake and fjord populations of calanoid copepods Limnocalanus macrurus and Drepanopus bungei in the Canadian high Arctic

The zooplankton assemblages of Lake A and Disraeli Fjord, northern Ellesmere Island (83°N, 75°W), were surveyed in early summer 1999. In permanently ice-covered Lake A, two glacial relict calanoid copepod species (Drepanopus bungei and Limnocalanus macrurus) were found in the top 30 m. All developmental stages of the more abundant D. bungei were present, whereas only adults of L. macrurus were found. Analysis of gut contents showed that L. macrurus preyed upon the smaller species. A net tow sample of zooplankton from Disraeli Fjord was mainly composed of D. bungei and L. macrurus, along with two marine cyclopoid copepods (Oncaea borealis and Oithona similis). These two zooplankton communities occur within unusual environments that are strongly influenced by perennial ice and snow. They will be subject to major habitat disruption should the current warming trends continue in the north polar region.     

An analysis of the loss of acroporid corals at Looe Key,Florida, USA: 1983–2000

The Caribbean reef-building corals Acropora palmata and Acropora cervicornis have undergone widespread declines in the past two decades, leading to their designation as candidates for listing under the United States Endangered Species Act. Whole-reef censuses in 1983 and 2000 at Looe Key National Marine Sanctuary in the Florida Keys provide estimates of areal loss of live Acropora spp. cover. Area (square meters) of live coral cover was quantified from depiction on scaled base maps of extent of coral cover observed by a snorkeler on each reef spur at each census. Certain thickets appear to have been persistent (though none expanded), but the total area of live A. palmata at Looe Key is estimated to have declined by 93% and A. cervicornis by 98% during this 17-year interval. It is likely that acroporid populations may have already undergone substantial decline prior to our initial census in 1983.     

Local and regional dynamics of a specialist herbivore: overexploitation of a patchily distributed host plant

This study reports a rare example where a native herbivorous insect frequently overexploits local populations of its perennial host. Local dynamics of a flightless weevil (Hadramphus spinipennis, Curculionidae) and its host plant (Aciphylla dieffenbachii, Apiaceae) were assessed for one discrete patch. In this main study site local weevil population structure, dynamics and movement were investigated using a capture-recapture study. Local plant dynamics were studied by mapping plant location, size, sex and the phenological stage of each plant. Regional weevil and plant dynamics were studied for six plant patches using line-transect counts to estimate local weevil numbers and repeated counts of the number of flowering adult plants to assess plant numbers. Dispersal was assessed by regularly searching all plant patches for marked weevils that emigrated from the main study site. Prior to extinction, local weevil abundance, survival and recruitment rates increased continuously. At the same time the feeding damage on the plants increased and the area covered by A. dieffenbachii decreased until no plants were left. An increase in weevil abundance was clearly associated with the extinction of the local host plant population. Weevils stayed in their local host plant patch whilst food was available and dispersed only after local extinction of the plant. Over a 4-year period four local population extinctions were observed. This study was too short to allow explicit conclusions to be drawn about the ratio of extinction to colonisation rates for both the weevil and the host plant populations. However, persistence of this locally unstable system appears possible only in a fragmented habitat where asynchrony in local dynamics is maintained.     

Trade-off between plant growth and defense? A comparison of sagebrush populations

We used ecotypic variation in big sagebrush (Artemisia tridentata) to examine potential trade-offs between inherent growth rate and tolerance or resistance to herbivory. Seeds were obtained from seven geographic populations, and 1,120 seedlings were established in a common garden. In one set of plots, plants were subjected to five treatments: control, regular insecticide spray, moderate browsing, severe browsing, or moderate browsing plus insecticide. Plants in a second set of plots were all untreated, and were used to estimate ambient growth, flower production, and susceptibility to herbivorous insects. In the first growing season, population differences in relative growth rate produced approximately seven-fold variation in mean biomass. Two populations of basin big sagebrush (A. tridentata tridentata) and one population of mountain big sagebrush (A. tridentata vaseyana) grew fastest; those of Wyoming big sagebrush (A. tridentata wyomingensis) showed the slowest growth. Bi-weekly application of insecticide for two growing seasons had no effect on the growth of either browsed or unbrowsed plants. All populations showed compensatory growth (but not overcompensation) in response to browsing, but the degree of compensation was unrelated to inherent growth rate. Similarly, there was no consistent relationship between plant growth rate and flower production in the second growing season. Some insects colonized fast-growing populations more frequently than slow-growing ones, but patterns of insect colonization were species-specific. At the level of geographic populations and subspecies, we found little evidence of a built-in trade-off between inherent growth rate and the ability to tolerate or resist herbivory. Because population ranks for growth rate changed substantially between seasons, attempts to correlate growth and defense characters need to account for differences in the growth trajectories of perennial plants.     

Constancy and asynchrony of Osmoderma eremita populations in tree hollows

A species rich beetle fauna is associated with old, hollow trees. Many of these species are regarded as endangered, but there is little understanding of the population structure and extinction risks of these species. In this study I show that one of the most endangered beetles, Osmoderma eremita, has a population structure which conforms to that of a metapopulation, with each tree possibly sustaining a local population. This was revealed by performing a mark-release-recapture experiment in 26 trees over a 5-year period. The spatial variability between trees was much greater than temporal variability between years. The population size was on average 11 adults tree^-1 year^-1, but differed widely between trees (0-85 adults tree^-1 year^-1). The population size in each tree varied moderately between years [mean coefficient of variation (C.V.)=0.51], but more widely than from sampling errors alone (P=0.008, Monte Carlo simulation). The population size variability in all trees combined, however, was not larger than expected from sampling errors alone in a constant population (C.V.=0.15, P=0.335, Monte Carlo simulation). Thus, the fluctuations of local populations cancel each other out when they are added together. This pattern can arise only when the fluctuations occur asynchronously between trees. The asynchrony of the fluctuations justifies the assumption usually made in metapopulation modelling, that local populations within a metapopulation fluctuate independently of one another. The asynchrony might greatly increase persistence time at the metapopulation level (per stand), compared to the local population level (per tree). The total population size of O. eremita in the study area was estimated to be 3,900 individuals. Other localities sustaining O. eremita are smaller in area, and most of these must be enlarged to allow long-term metapopulation persistence and to satisfy genetic considerations of the O. eremita populations.