This communication provides an illustration for the use of computer simulations in human immunology. When traditional experiments are impossible, unethical, or unfeasible, in silico modeling procedures may help to fill the gaps in our knowledge of an immune system response to a pathogen. In our study, we define terms and properties of modeled entities: "a clonotype", its distribution, and rank-frequency summaries, and describe properties associated with each of these three clonotype-related entities. We simulate a multistage dynamic process of an immune memory response to influenza. We believe that illustrated properties of fractality and self-similarity might arise due to the following process. The memory T cells operate in a complex environment of shifting pathogen concentrations, increasing and then decreasing inflammatory signals, and multiple interactions with other immune cells and their infected targets. Therefore, a fractal structure to such a population would represent an optimization in terms of percolation into immune/inflammatory space.
The inference of the interactions between organisms in an ecosystem from observational data is an important problem in ecology. This paper presents a mathematical inference method, originally developed for the inference of biochemical networks in molecular biology, adapted for the inference of networks of ecological interactions. The method is applied to a network of invertebrate families (taxa) in a rice field.
Landscape structure influences local diversity and ecosystem processes, including cross-habitat fluxes of organisms coupling the dynamics of different habitats. The flow of organisms across system boundaries is known to occur between different natural habitats as well as across the crop¿noncrop interface. Several studies show how field boundaries can enhance predator populations invading arable crops and controlling pest populations. However, generalist arthropods may also spill over from land-use systems to natural areas (mainly grassland) modifying interactions therein. A view of land-use systems as sources and natural habitats as sinks is consistent with the idea that the direction of the organismsâ¿¿ fluxes is from high to low productivity systems, while noncrop habitats are important sources for recolonization of arable fields after they are cleared for harvest. From the perspective of landscape management, enhancement of population exchanges between crop and noncrop areas may include beneficial as well as unwelcome interactions
Conventional chlorine bleaching affected survival of young larvae. External treatment, introduction of oxygen pre-bleaching and increased substitution of active chlorine as chlorine dioxide decreased or eliminated mortality. The growth pattern of the larvae differed markedly with time and effluent type; externally treated BKME from conventional chlorine bleaching caused a slower growth, oxygen prebleaching (treated/untreated effluent) sequentially inhibited and stimulated growth. Increased use of chlorine dioxide did not cause any effect upon growth. Total body fat content and liver histological analysis indicated a positive correlation between affected growth and metabolic disturbances. Exposed fish were also more infested with parasites. -from Author
At a location N of the Hanko Peninsula, Gulf of Finland, vertical migration mainly occurs from the middle of July to the beginning of October. Onset corresponds to the time when cessation of growth occurs, and it may be related to a depletion of the locally available food supply. During the main period of vertical migration, large week-to-week fluctuations occur that appear related to out- and inward movements of the water caused by changes in sea level. The whole population generally takes part in the migration. -from Authors
While much is known regarding the role of chemical alarm cues in the mediation of predator–prey dynamics within aquatic ecosystems, little is known regarding the production of these critically important information sources. In a series of laboratory experiments, we tested the possible effects of diet, body condition and ontogeny on the production of chemical alarm cues in juvenile convict cichlids (Archocentrus nigrofasciatus, Cichlidae, Acanthopterygii). Juvenile cichlids were fed one of two diets, tubifex worms (Tubifex spp.) or brine shrimp (Artemia spp.). Shrimp fed cichlids grew longer and heavier and were in better condition than were tubifex fed cichlids. In Experiment 1, cichlids exhibited a stronger antipredator response to conspecific skin extracts from donors fed shrimp versus tubifex, regardless of test cichlid diet. In Experiment 2, juvenile cichlids were exposed to the skin extracts of high versus low condition donors fed either tubifex or shrimp diets. Cichlids exhibited a significantly stronger antipredator response to skin extracts of high condition donors, regardless of donor diet. Finally, in Experiment 3, juvenile cichlids were exposed to skin extracts of similar sized juvenile conspecifics, adult conspecifics, swordtail (Xiphophorus helleri) or a distilled water control. We found no evidence of an ontogenetic change in the production of alarm cues as cichlids exhibited similar intensity antipredator responses when exposed to juvenile and adult conspecific alarm cues. Taken together, these data suggest that individual diet may influence body condition with the consequence of influencing chemical alarm cue production in juvenile cichlids.
Predation is an important agent leading to the evolution of accurate risk assessment. In fishes, one of the best studied modes of threat assessment is the use of damage release cues from consumed or damaged individuals. These cues act as sources of public information alerting both conspecific and heterospecific individuals in the immediate area of a possible predation threat. Responses to damage release cues can be behavioural (e.g. avoidance of the cue or increased schooling), morphological (e.g. change in body shape), and potentially reproductive (e.g. altered patterns of breeding and reproductive investment). In the current study we documented the response of convict cichlids (Archocentrus nigrofaciatus) to damage release cues from conspecifics, unknown heterospecifics (swordtail, Xiphophorus helleri), and distilled water. In short term behavioural trials we found that cichlids exhibited an antipredator response to injured conspecifics, while they exhibited a foraging response to injured swordtails and no response to distilled water. In longer term trials (41 days) we found that cichlids exposed to conspecific cues grew significantly less than those in the other treatments. Finally, we found that reproductive patterns were influenced by the treatments. Cichlids bred faster in the presence of predation cues (conspecific skin extract) and food cues (swordtail skin extract) than the control treatment (distilled water).
Ann. Zool. Fennici, vol. 32, 117-121 Activity patterns and size of home ranges were studied in the American mink (Mustela vison) by the means of radiotracking in sea archipelago in southern Finland. Activity pattern was analyzed in 7 tracking periods of individual minks in a different times of the year: 1 was nocturnal, 2 were diurnal and 4 were neutral. Total activity was negatively correlated with night length. Home range size varied largely according to season and sex, for instance. The paper discussed some details about the use of home ranges consisting of several islands and skerries.
The ground parrot (Pezoporus wallicus) is a vulnerable species that occurs in isolated pockets of heathland and sedgeland of Australia. This study used randomly amplified DNA fingerprinting (RAF) to examine genetic diversity in the eastern population of the ground parrot. The seven primers used produced an average of 68 markers per primer, and the number of unambiguous polymorphic markers per primer averaged 6.3 (9.2%). Overall genetic similarity was 0.978 ? 0.03. The low level of genetic diversity revealed by RAF is comparable to the lower end of diversity found in species that are declared endangered.
In many plants and animal species, asexuals are more common in marginal habitats such as high latitudes or altitudes than their closely related sexual counterparts. Here we propose a new hypothesis to explain this pattern called "geographic parthenogenesis". In marginal habitats, populations may often exist as metapopulations with high degrees of subdivision and local extinction and recolonization, resulting in genetic bottlenecks during colonization. Our hypothesis states that such dynamics could play a key role in geographic parthenogenesis. Genetic bottlenecks and subsequent drift have stronger negative fitness consequences in sexuals than in asexuals because genetic drift leads to increased homozygosity and inbreeding depression in sexual but not in asexual populations. Migration, leading to inter-population hybridisation, may induce temporary fitness recovery in sexuals. Asexuals arising from such hybrids have an increased likelihood of invading sexual populations because they keep their high fitness, whereas the fitness of sexuals is doomed to decrease due to subsequent inbreeding and inbreeding depression. Therefore, asexuals may replace sexuals in subdivided habitats with local extinction and recolonization while they would not succeed in unstructured habitats without local turnover dynamics.
Ann. Zool. Fennici, 0003-455X, vol. 29, 161-167 In laboratory tests the pair formation of the sexually size dimorphic and colour polymorphic isopod Idotea balthica was non-random with respect to size, whereas colouration had hardly any effect on mate choice. When given a choice of two females, 70% of the males selected the larger female for precopula. In experimental populations, however, female size had no evident effect on mate choice, so that further confounding effects may complicate the pair formation in natural heterogenous habitats. Precopulatory males were larger than solitary males in the experimental populations, both in female and male-biased populations. The larger size of precopulatory males may at least partly result from male-male competition, but the females may also affect the precopulatory success of the males in a size-dependent manner. Consequently, presumably both intrasexual and intersexual interactions favour larger males in I. balthica. Female size, on the other hand, may be only a second choice after female maturity. The male-biased sex ratio in early summer may in particular discourage males from being too size selective.
The sexual dimorphism in size developed very early during the immature stage. Males and females also showed different patterns during maturation. The relative weight gain of females was continuously higher during maturation, whereas males had higher total food consumption that females. At the beginning of maturation males allocated a larger proportion of ingested material to the production of new biomass, but this later changed as the production efficiency of males declined towards the breeding season. Males are likely selected for larger size and higher activity influencing mating success; females are selected for a higher production efficiency before breeding and for minimizing the costs of reproduction. Gravid and non-ovigerous females allocated about the same proportion of ingested material to the production of new biomass. The reduced food consumption of gravid females may be a mechanical consequence of incubation and/or it may reflect a decline in the mobility and activity of gravid females. -from Authors
Ann. Zool. Fennici, vol. 35, nr. 1, 1998 We studied the reproductive performance of herring gulls (Larus argentatus) in an old stable colony in SW Finland. Over the period 1993-1997, the coliny decreased, and the garbage dumps the birds may have utilised all closed. This had an effect on the breeding performance of the colony when comparing the year prior to the closing of the last garbage dump available (1996), and the following season (1997). It is clear that the last-laid egg size decreased significantly between years, more eggs were lost due to predation, and fewer of the hatched young fledged. The quality (in terms of body weight) of hatching chicks (both first and last) was not reduced, but first chicks grew slower in 1997. These changes are in agreement with predictions from other studies, and are likely effects of diminishing food resources. However, overall production was still good, and the birds seem capable of successful breeding without the presence of nearby garbage dumps. Affiliation: University of Helsinki Department of Ecology and Systematics P. O. Box 17 00014 Helsingin yliopisto Finland
The mesowear method assesses the dietary regime of herbivorous mammals based on the attrition/abrasion equilibrium by evaluating cusp shape and relief of upper second molars. The method has recently been extended to include four tooth positions, upper P4-M3, in equids. In this study we determine whether the method can be extended in ruminants by applying it to maxillary and mandibular dentitions of a browser, the giraffe (Giraffa camelopardalis) and two mixed feeders, the oribi (Ourebia ourebi) and the musk ox (Ovibos moschatus). We find that including the upper third molar in addition to the upper second molar provides consistent mesowear classifications in these species. Lower dentitions of mixed feeders score significantly differently in terms of mesowear as compared with upper dentitions. We infer that adaptive optimization in differential anisodonty is related to the composition of the diet and should be mirrored in differential mesowear signals of adjoining upper and lower molars. Our results suggest that in mixed feeders, sharpness is maximized in upper teeth, whereas in specialized feeders this is not the case.
Faunal and floral diversity tends to increase on Northern Baltic islands with increasing island area, but even within a single group of species there is no general species-area relationship. For example, within an area studied, species number in vascular plants was higher on clustered islands (0.1-1.0 ha) than on more scattered, similar-sized islands. For most taxa island colonization in the N Baltic area is easy owing to the short distances between islands and the mainland, whereas long-term persistence on the islands might be difficult either due to lack of suitable habitats or due to harsh climate and probably occasionally due to biotic causes. Pioneering species colonize small islets and shorelines emerging from the sea, but they disappear from the central areas where species of more mature communities displace them. It follows that species colonizing the smallest islets are also found on almost any other islands irrespective of island size. This pattern seems to hold for a number of taxa ranging from vascular plants to breeding birds. Rock-pools, small island-like aquatic ecosystems on Baltic islands harbor a rich fauna and flora. Though many of the species occupy different parts of the salinity gradient, quite a number have overlapping preferences. Factors contributing to the coexistence of those species are mosaic-like distribution and dynamic disappearance (droughts) and reappearance (in rains) of the rock-pools. These characters promote coexistence of good colonizers and poor competitors with good competitors but poor colonizers. -from Authors
Metacercariae, mainly of Lacunovermis macomae were present in Macoma balthica taken from sites where depth varied between 5-40 m and the salinity between 2-7per mille. Metacercariae were present even in specimens of 4-6 mm shell length. The infection incidence (% of infected individuals from those studied) and degree (number of metacercariae/shell valve) usually increased in conjunction with shell length increase. Infection incidence attained 100% in most collection sites when the shell length was >12 mm, and coincidently heavily infected individuals (= or >30 metacercariae/shell valve) began to appear. -from Author
Ann. Zool. Fennici, vol. 32, 411-419 The effects of several environmental factors on the relative year-class strength variations of pikeperch (Stizostedion lucioperca (L.)) were studied in a shallow brakisch Baltic Bay in Helsinki, Finland, during 1971-1990. The year-class strength correlated positively with the mean summer water temperature from June to September during the first year of life. Negative correlations between the year-class strength and wind indices were found with the southerly and southwesterly winds in July. These winds explained 35% (F = 4.35, P = 0.027, n = 20) and the mean temperature alone 40% (F = 9.89, P = 0.007, n = 17) of the total variation in year-class strength. When the exeptionally weak year-class in 1971 was excluded from the analysis, the correspondence values were 62% for the winds (F = 6.50, P = 0.007, n = 19) and 55% for the mean summer temperature alone (F = 16.92, P < 0.001, n = 16). No correlation existed between the year-class strength and water level, water salinity or water transparency.
Annales Zoologici Fennici, vol. 34, nr. 3, 205-212 The spionid polychaete Marenzelleria virjdis (Verrill 1873) was for the fast time ob-served in the Finnish coastal waters at the entrance of the Gulf of Finland in 1990. During 1990- 1993 M. viridis expanded its distribution into the eastern parts of the Gulf of Finland and into the southern part of the Gulf of Bothnia. Its introduction into the Baltic Sea has probably occurred through ship transport, as all the first findings are connected to harbour areas. Although the abundance and biomass of M. viridis is comparatively low the species seems to have become a permanent member of the macrozoobenthos in the northern Baltic.
Annales Zoologici Fennici, ISSN 0003-455X, nr. 27, 297-301 The deposit-feeding Pontoporeia affinis (Lindström) and P. femorata (Kröyer) (Crustacea, Amphipoda) are the dominant macrobenthic animals in deep soft bopttom areas of the northern Baltic Sea. Their abundance, growth and life cycle vary according to local temperature and food conditions. Both species seem to be food-limited. In the Tvärminne area, on the southwest coast of Finland, the seasonal timing of growth differs between species, indicating either competition or differing food sources. Abiotic and biotic factors regulating Pontoporeia populations make up an intertwinded network, with numerous one-way effects and two-way interactions. The omnivory of Pontoporeia on three successive levels (sediment detrital carbon, bacteria and meiofauna) confuses predator-prey and competitive relationships in the detritus-based benthic system. Calculations based on the observed growth and production show that Pontoporeia species must obtain most of their energy requirements from detrial carbon. Nonselective feeding by Pontoporeia decreases the populations of bacteria and the meiofauna, and thus probably releases Pontoporeia from their competition for the detrital carbon source, but at the same time decreases the availability of high quality food. Biology and Ecology of Glacial Relict Crustacea Tvärminne 1988
Predation by small mustelids is widely considered to be the most likely mechanism to maintain multiannual fluctuations of vole populations in Fennoscandia. Apart from the direct effect of predation, small mustelids have been suggested to have indirect effects on vole population dynamics. We studied in a field experiment the indirect effects of the presence of the least weasel (Mustela nivalis nivalis) on behaviour and demography of field voles (Microtus agrestis). We constructed grids made of drainpipe with small holes and covering an area of 0.24 ha (4 * 6-m grid, pipes with 10-m intervals). A least weasel moved in the experimental grid without having access to voles during the entire experiment, lasting for 11 weeks. We analysed the rate of maturation, breeding success, movements, and home range use of field voles in the experimental and control grids. The results indicate that weasel's presence had no or had only minor effects on voles.
We present an example of how systematic studies of habitat loss thresholds at multiple scales can be used for assessing the functionality of habitat networks. The different steps are: (1) carefully select a suite of species representing each land cover type; (2) use quantitative targets based on the requirements of the focal species at multiple scales; (3) make regional gap analysis for the different land cover types; (4) use habitat modelling to build spatially explicit maps describing the probability that existing habitat patches really contribute to the functional connectivity of that theme in the landscape. The latter is important, since gap analyses alone neglect aspects like the quality, size, duration and configuration of land cover patches, and therefore overestimate the amount of functional habitats. The presence of thresholds at different scales suggests that the conservation management should be planned in a spatially explicit way.
Biodiversity monitoring provides guidelines for decisions on how to manage biological diversity in terms of production and conservation. Monitoring determines the status of biological diversity at one or more ecological levels and assesses changes over time and space. Monitoring at the global level is needed to compare trends caused by the increasing homogenisation of the world’s landscapes. Bioindicators are routinely used, but each indicator’s potential to determine changes in the overall biodiversity should be rigorously tested. Monitoring is a vital feedback link between human actions and the environment, but incorporation of monitoring results into decision making is hampered by poor communication between ecologists and decision-makers. A global network for assessing biodiversity changes (GLOBENET) is described as an example of an initiative that attempts to address the above issues by using a simple field protocol with the aim to develop tools for assessment and prediction of the ecological effects of human-caused changes in the landscape.
The study of host-symbiont interactions has mainly focused on how parasites influence the fitness and behaviour of their host. Two common assumptions of such studies are that all symbiontic organisms are parasites, and that they are directly or indirectly re- lated to host traits which act as signals of quality in mate choice. We assessed the prevalence and abundance of feather mites (Proctophyllodes pinnatus; Astigmata; Pro- tocphyllodidae) on Linnets (Carduelis cannabina; Aves; Carduelinae) and examined how the abundance of mites may be related to the condition and plumage colour of Linnets. Mite prevalence was so high (near 100%) that no variation could be found between age classes or sexes. However, mite abundance was significantly higher in males than in females. No significant relationship was found between mite abundance and host nutritional condition, except for yearling females. Nutritional condition and showiness of secondary sexual traits (carotenoid-based plumage patches) were not cor- related in male linnets. Size and brightness of red patches in the plumage of males varied with age, but were unrelated to mite abundance when age was taken into ac- count. The absence of effects of mites is in agreement with the long held, neglected view that feather mites form non-parasitic associations with birds. Higher mite abun- dance on males may be attributed to more secretions of the uropygial gland, on which mites feed. Gender variation in plumage colour and abundance of feather mites sug- gests a common hormonal-mediated mechanism regulating both traits.
Ann. Zool. Fennici, vol. 34, nr. 1, 31-36 We sampeld blue mussels (Mytilus edulis) in 1992-1996 from mussel beds that common eiders (Somateria mollissima) preferentially use during foraging in the Hanko archipelgo, Finaland. We also compared our data with an earlier study carried out in the same area. We found a consistent trends towards decreasing mussel size: the proportion of larger mussels in the population has decreased significantly. Since blue mussels are an essential part of the Baltic ecosystem, a shift in mean mussel size may have important consequences. A decrease in salinity during the last few decades may be ultimate reason for the observed changes, as salinity affects growth, maximum size and reproduction of mussels. We also suggest that selective eider predation may be of local importance. Affiliation: University of Helsinki Department of Ecology and Systematics P. O. Box 00014 Helsinki University Finland
Ann. Zool. Fennici, vol. 32, 175-182 I censused colonies (15 sites) of Common Gulls in the northern Baltic, Hanko, in 1978-91. The total population in the area declined from 240 to 159 pairs. Reproductive success was low in many colonies for several years during the study period. The mean rate of fledged young per pair varied from 0.17 to 1.09 (1982-91). The reproductive failures were mainly due to predation by Mink, and Herring Gull. When minks appeared to decline in numbers, production rose significantly. With respect to predation risk, colony sized varied very much. During 8 years (1982-89) some colonies were never subject to major disturbances, while some colonies were severely disturbed in most years. The colonies disturbed most declined rapidly, while colonies successful in most years gained pairs, inspite of a general decreasing trend. I suggest that this was due to relocation of breeders between colonies in the area. The rate of decline was also tied to the severity of the disturbance, when adults were threatened, rapid desortion of a colony site may follow, when chicks are taken, the desertion process is slower. This is lakely due to the Common Gull being adapted to stable breeding environments favouring site tencity. I suggest that the colonies formed an interactive metapopulation-like system, which is significant for understanding how archipelago birds in the Baltic should best be protected.
Hatching success, brood survival and predation rates of red grouse chicks were examined at four sites in north-east Scotland over two years (1994--1995). Two of these sites have previously been the focus of a large-scale population study on grouse during the late 1950s enabling a comparison to be made. A total of 85 hens were radio-tracked and their breeding success monitored over the two years. Compared with studies undertaken in the 1950s, mean clutch size had risen from 7.2 to 8.6 eggs. Of the 76 nests monitored, 17 (22.4%) broods were lost either through egg or chick predation or by the adult being taken by a predator during incubation. Stoats appeared to be responsible for the largest amount of egg predation. There was a significant increase in predation levels, although hatching success was not significantly different from the 1950s. Chick mortality was highest within the first ten days, a similar result to that found in the 1950s. Overall, mean brood survival from hatching to 20 days was 55.1%. Possible reasons for larger clutch sizes, and the apparent increase in predation levels, are discussed.
The Glanville fritillary (Melitaea cinxia) has been studied in Finland within an area of 50 by 70 km since 1993. We analyse 11-yr time series for aggregate populations in 20 squares of 4 by 4 km. Different aggregate populations exhibit dissimilar long-term trends, including significant increasing and decreasing trends as well as stable population sizes, and their average size is significantly related to the amount of habitat but not of host plants. Precipitation shows spatially correlated variation in the study area, recorded with high-resolution weather radar. Spatial variation in August and June precipitation explains a significant amount of spatial variation in the dynamics of aggregate populations. Many processes operating in local populations have strong effects, but these effects are not consistent in time and space and they often counter each other, making it less likely that one would detect a signal of local processes in large-scale data for aggregate populations.
Range expansion of ectoparasites can cause parasites to attack new host species. In these cases it is important for the parasite to be able to adapt to the new environment and to reproduce on the host. For the host, it is crucial to hinder successfully the development of long-lasting parasitic relationship. The deer ked ( Lipoptena cervi) is a novel ectoparasite for northern cervids. We investigated of the deer ked can use the reindeer (Rangifer tarandus) as a host and, if it can, wether antiparsitic treatment against this parasite would be available. Three groups of reindeer were monitored: two groups of 6 reindeerr were infected with 300 flies per each individual; a control group comprised 6 animals. One of the infected groups was treated with subcutaneous ivermectin. At the end of the experiment the infextation rate of the infected animals was low. The reindeer in the non-treated group had both live and dead deer keds and also a single pupa while the ivermectin-treated reindeer had only dead deer keds. As some deer keds survided and reproduced, thedeer ked can potentially use the reindeer as a host but antiparasitic treatment may be effective agains this parasite.
Annales Zoologici Fennici, ISSN 0003-455X, nr. 27, 207-210 Chromosome numbers and karyological characteristics were examined during spermatogenesis in Saduria entomon (n=30), Mysis relicta (n=52), Pontoporeia femorata (n=14) and P. affinis (n=26) from the northern Baltic Sea, and in Mysis relicta (n=52), Pallasea (Pallasiola) guadrispinosa (n=26) and Gammaracanthus lacustris (n=19) from Lake Pääjärvi, southern Finland. The chromosomes of the postglacial immigrants Gammarus lacustris and G. pulex were also recorded (n=26). These observations suggest karyological differentiation of the originally subarctic marine amphipods Pontoporeia femorata and Gammaracanthus lacustris from Pontoporeia affinis, Pallasea quadrispinosa and Gammarus spp. evolved in Palearctic freshwater bodies. Biology and Ecology of Glacial Relict Crustacea Tvärminne 1988
We conducted laboratory experiments (1) to confirm the existence of a non-injury released disturbance cue in juvenile convict cichlids and rainbow trout, and (2) to determine if cichlids and trout exhibit a graded threat-sensitive antipredator response to varying concentrations of disturbance cues. The results of our first experiment demonstrate that both cichlids and trout exhibit significant antipredator responses (reductions in time spent moving, foraging rate and area use) to the odour of conspecifics that had been exposed to a realistic predator model but not to the odour of undisturbed conspecifics. The results of our second experiment demonstrate that cichlids and trout exhibit reduced time spent moving and foraging rates proportional to the concentration of disturbance cue detected. Together, these results confirm the presence of disturbance cues in cichlids and trout and demonstrate that disturbance cues provide sufficient information to allow for graded threat-sensitive responses.
The Glanville fritillary butterfly (Melitaea cinxia) in Finland feeds on the plants Plantago lanceolata and Veronica spicata. These two plant species are distributed heterogeneously and both vary spatially and temporally in iridoid glycoside concentrations. We investigated the associations of plant species and iridoid glycoside (aucubin and catalpol) concentrations with weight, development rate and survival of larvae of the Glanville fritillary under laboratory conditions. In one experiment we compared the performance of split brood groups of larvae feeding on the two plant species collected from natural populations. In the second experiment larvae were fed P. lanceolata lines laboratory selected for high and low aucubin and catalpol concentrations. Larvae fed V. spicata performed better in terms of survival, weight and growth rate than those feeding on P. lanceolata, regardless of iridoid glycoside concentration. However, in the second experiment iridoid glycoside concentration in P. lanceolata was positively associated with larval performance. High iridoid glycoside concentrations retarded development rate of the first instar larvae, whereas later on the development was accelerated by higher concentrations of these compounds. The spatial and temporal variation of plant species suitability and iridoid glycoside content, and larval family level effects of plant chemistry on performance convey a dynamic ecological and evolutionary relationship between these host plants and their specialized herbivore.
Research on predator-prey relationships in the littoral zone of Lake Constance showed that eels (Anguilla anguilla (L.)) were the most numerous piscivorous predators in the shallow water zones up to 3-metres depth in 1992. From July on fish was the most important component of the diet of eels. Perch (Ferca fluviatilis L.), burbot (Lota Iota (L.)) and bream (Abramis brama (L.)) were the most frequently consumed fish. As 61% of all identifiable fish the eels had consumed were perch, an attempt was made to estimate the impact of eel predation on the young-of-the-year (y-o-y) of the perch population. Consumption by the total eel population never exceeded the amount of perch fry consumed by adult, cannibalistic perch estimated in other studies, but it seems possible that eel predation could have an adverse influence on weak year classes. Further reoligotrophication of the lake might lead to even higher fish consumption by the eels due to declining benthic production and consequent increased predation pressure.
Size distributions of cohorts of pikeperch and perch originating from three lakes in the Netherlands were compared to test the hypothesis that skewness or bimodality within cohorts of pikeperch and perch develops especially in environments with a discontinuous size distribution of their potential food items. In older, more eutrophic lake ecosystems like Tjeukemeer and IJsselmeer, where macro-invertebrates occur in low densities, 0-group pikeperch generally exhibit differential growth of fast-growing piscivores and slow-growing zooplanktivores. The size distributions of such cohorts become positively skewed during their first summer and often become bimodal at the end of the growing season with modes at ca. 10-15 cm and 6-8 cm, respectively. The size attained by zooplanktivorous 0-group perch in these systems is relatively small (6-9 cm) and is positively related to summer temperature. Cohorts of perch in these systems shift to piscivory, partially or totally, in their second or third summer. The differential growth of zooplanktivorous and piscivorous perch of the same cohort can cause a broadening and a positive skewness in the cohort size distribution, but never results in a bimodal size distribution. In the recently freshened, mesotrophic Volkerak ecosystem, the initial high availability of the macro- invertebrate Neomysis integer, in the first couple of years enabled 0-group pikeperch and perch to reach similar large sizes of 12-14 cm and to both switch to piscivory in their second summer. After ca. 5 years Volkerak became more eutrophic, the stock biomass of cyprinids increased, the size distribution of 0-group pikeperch became bimodal and the 0-group perch stayed small (< 10 cm), as in the older, more eutrophic systems. It is postulated that more productive systems with a higher fish biomass, but with lower biomasses of macro-invertebrates and less large-sized zooplankton probably have stronger selection mechanisms for recruiting percids.
Species experience landscapes differently depending on their needs and behaviors, and on their trophic level. We expect species at high trophic levels in a community to be more sensitive to habitat fragmentation than species at lower trophic levels. But this depends on attributes such as resource breadth, dispersiveness, reproductive rate, and longevity, which may not be related to trophic level. I address the association of fragmentation with trophic level using a literature review of 31 studies of herbivores and their natural enemies, and a case study of the parasitoids associated with the Glanville fritillary butterfly. Measures of species richness or total parasitism in an entire insect community provide the strongest support for the idea that negative effects of fragmentation amplify at higher trophic levels. Generally though, there is great variation among studies, due to variation among species, as well as in designs of both experimental and observational studies.