Competition, predation and species responses to environmental change

Despite much effort over the past decade on the ecological consequences of global warming, ecologists still have little understanding of the importance of interspecific interactions in species responses to environmental change. Models predict that predation should mitigate species responses to environmental change, and that interspecific competition should aggravate species responses to environmental change. To test this prediction, we studied how predation and competition affected the responses of two ciliates, Colpidium striatum and Paramecium tetraurelia , to temperature change in laboratory microcosms. We found that neither predation nor competition altered the responses of Colpidium striatum to temperature change, and that competition but not predation altered the responses of Paramecium tetraurelia to temperature change. Asymmetric interactions and temperature-dependent interactions may have contributed to the disparity between model predictions and experimental results. Our results suggest that models ignoring inherent complexities in ecological communities may be inadequate in forecasting species responses to environmental change.     

Diversity measurement combining relative abundances and taxonomic distinctiveness of species

We discuss a diversity measure combining information of relative abundances and taxonomic distinctiveness suggested by Ricotta (2004). We show that Ricotta's measure violates weak species monotonicity, a condition that requires that the addition of a species should always increase a diversity index if abundances change only marginally. We suggest an alternative index satisfying weak species monotonicity and apply it to the 'Zeesserveld' forest reserve in the Netherlands.     

Distribution,species composition and relative abundances of sandflies in North Waziristan Agency,Pakistan

This study was conducted to investigate the diversity of sandflies (Psychodidae: Phlebotominae) and the incidence of leishmaniasis in three villages of North Waziristan Agency, Pakistan. Sandflies were sampled monthly during 2012, at dusk and dawn, in selected indoor habitats including both bedrooms and animal sheds using a knock‐down spray catch method. A total of 3687 sandflies were collected, including 1444 individuals in Drezanda, 1193 in Damdil and 1050 in Dattakhel. This study revealed 14 species of two genera, Phlebotomus (Phlebotomus sergenti, Phlebotomus papatasi, Phlebotomus caucasicus, Phlebotomus kazeruni, Phlebotomus alexandri and Phlebotomus salehi) and Sergentomyia (Sergentomyia dentate, Sergentomyia baghdadis, Sergentomyia babu, Sergentomyia theodori, Sergentomyia sumbarica, Sergentomyia dreyfussitur kestanica, Sergentomyia hogsoni pawlowskyi and Sergentomyia fallax afghanica) (both: Diptera: Psychodidae). Phlebotomus sergenti was the most abundant species (42.1%), followed by S. dentata (17.7%) and S. baghdadis (17.4%). The number of males collected represented about twice that of female flies, and the maximum number was collected in July, followed by August. The determination of the species composition of sandfly populations, seasonal variations, relative abundances and estimations of infection in the vector population may provide information about the dynamics of leishmaniasis transmission that is useful in planning vector control activities.     

A parametric diversity measure combining the relative abundances and taxonomic distinctiveness of species

Most ecological diversity indices summarize the information about the relative abundances of species without reflecting taxonomic differences between species. Nevertheless, in environmental conservation practice, data on species abundances are mostly irrelevant and generally unknown. In such cases, to summarize the conservation value of a given site, so‐called ‘taxonomic diversity’ measures can be used. Such measures are based on taxonomic relations among species and ignore species relative abundances. In this paper, bridging the gap between traditional biodiversity measures and taxonomic diversity measures, I introduce a parametric diversity index that combines species relative abundances with their taxonomic distinctiveness. Due to the parametric nature of the proposed index, the contribution of rare and abundant species to each diversity measure is explicit.     

Instar-specific mortalities of coexisting Daphnia species in relation to food and invertebrate predation

Instar-specific mortalities of Daphnia hyalina and D.cucullatawere studied from May 19 to September 29, 1988 in combinationwith invertebrate predator and phytoplankton abundance. Simultaneouslife-table experiments were conducted under semi-natural conditionsin the laboratory to estimate juvenile mortality in a predator-freeenvironment. Juvenile mortality by predation was calculatedas the difference between juvenile mortality in the field andin the experiments and was the most important factor for thedifferences in abundance of the two species. For D.hyalina juvenilemortality was higher in early summer and probably caused byselective predation by Chaoborus flavicans. Predation by Leptodorakindtii was probably more important during the rest of the summer.Estimated mortality by predation adequately explained juvenilemortality, except for a 3-week period in August. Decreasingflagellate densities in July were accompanied by increased juvenilemortalities of D.hyalina and D.cucullata in the life-table experimentsin August and coincided with a Daphnia population decrease.     

The relative importance of predation and competition in two reef fishes

Competition and predation may both strongly influence populations of reef fishes, but the importance of these processes relative to one another is poorly understood. I quantified the effects of predation and competition on the growth and survival of two temperate reef fishes, Lythrypnus dalli and Coryphopterus nicholsii, in field experiments in which I manipulated the densities of the two species and the abundance of predators (using exclosure cages) on small replicate patch reefs. I also evaluated the influence of predators on the behavior of the two species to help interpret the mechanisms of any predatory influences on growth or survival. Predation was much more important than competition (inter- or intraspecific) in Lythrypnus. For Coryphopterus, neither competition nor predation were particularly important. Behaviorally, both species responded to predators by reducing foraging rate and hiding. This altered behavior, however, had no repercussions for growth or survival of Coryphopterus. In contrast, Lythrypnus grew more slowly and suffered greater mortality when exposed to predators. Interspecific competition did not significantly influence either species. Intraspecific competition did not affect the growth of Coryphopterus, but survival tended to be lower at high densities. Growth of Lythrypnus was depressed by intraspecific competition, but survival was not, except that, in the presence of predators, survival was density dependent. In contrast to the historical emphasis placed on the role of competition, this study indicates that predation can be more important than competition in determining patterns of abundance of some reef fishes. For example, predators not only influenced foraging of both Lythrypnus and Coryphopterus, but they also reduced growth and survival of Lythrypnus, and therefore appear to help maintain the marked habitat segregation between the two species. Received: 16 June 1997 / Accepted: 3 December 1997     

Food and predation as major factors limiting two natural populations of Daphnia cucullata Sars

A detailed analysis of two euplanktonic populations carried out in the same period, 18 May–11 August, 1978, in two neighboring Mazurian lakes revealed different patterns of changes in population densities and significant differences in fecundity, age structure and mean sizes of individuals despite similar epilimnion temperatures in the lakes. Similar densities were maintained in both populations although food limitation was less important and predation more intense in one than in the other of the two lakes. The relative importance of food limitation and predation is discussed in lakes of low and high fertility. It is also suggested that both low food concentration and high selective predation pressure favors small clutch sizes in cladocerans.     

Quantifying the relative importance of variation in predation and the environment for species coexistence

Coexistence and food web theory are two cornerstones of the long‐standing effort to understand how species coexist. Although competition and predation are known to act simultaneously in communities, theory and empirical study of these processes continue to be developed largely independently. Here, we integrate modern coexistence theory and food web theory to simultaneously quantify the relative importance of predation and environmental fluctuations for species coexistence. We first examine coexistence in a theoretical, multitrophic model, adding complexity to the food web using machine learning approaches. We then apply our framework to a stochastic model of the rocky intertidal food web, partitioning empirical coexistence dynamics. We find the main effects of both environmental fluctuations and variation in predator abundances contribute substantially to species coexistence. Unexpectedly, their interaction tends to destabilise coexistence, leading to new insights about the role of bottom‐up vs. top‐down forces in both theory and the rocky intertidal ecosystem.     

Filamentous cyanobacteria alter the relative fitness in a Daphnia hybrid species complex

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Risk of predation for two reptile tick species

Experiments were conducted in the Mount Mary region of South Australia where the distributions of the two reptile-tick speciesAponomma hydrosauri andAmblyomma limbatum narrowly overlap. Engorged larvae and nymphs were placed in boxes with and without access to predators and left for 1 week. At two out of five sites there was greater loss from open access boxes in replicates during warmer periods of the year. Predation by ants appears to be the most likely explanation for the loss of ticks.     

Egg-hatch phenology and intraguild predation between two mantid species

Relative timing of egg hatch between two cooccurring, congeneric mantids, Tenodera angustipennis and T. sinensis, was experimentally manipulated in replicated field enclosures to test the importance of intraguild predation to survivorship and development of T. angustipennis. T. angustipennis is normally smaller than its congener because of later egg-hatch. Delaying introduction of T. sinensis relative to normal egg hatch phenology reduced mortality for T. angustipennis, but did not affect its rate of development. The results indicate that intraguild predation by normally earlierhatching T. sinensis can be an important factor in the early life history of T. angustipennis, but that interspecific competition is not a strong selective factor in developmental asynchrony between these two species.     

Competition, predation, and the distributions of four desert anurans

Several studies have shown that larval competition and susceptibility to predation affect distributions of amphibian assemblages across ephemeral and perennial habitats. However, few studies have examined mechanisms affecting distribution patterns and site use of anurans adapted to highly ephemeral habitats. This study examines hypotheses about competition and predation as mechanisms creating non-overlapping patterns of site use in four anurans that breed in highly ephemeral habitats: Scaphiopus couchii (Couch's spade-foot toad), Gastrophryne olivacea (narrow-mouthed toad), Bufo speciosus (Texas toad), and Bufo punctatus (red-spotted toad). These four anurans showed a significantly nonrandom pattern of co-occurrence. Only 12% of 95 ephemeral breeding sites surveyed were occupied by more than one species. We tested the hypotheses that non-overlapping use of breeding sites was due to activity rates of their tadpoles that in turn reflect their competitive ability and susceptibility to predation. Tadpoles of S. couchii were significantly more active and more susceptible to predation than were tadpoles of G. olivacea, B. speciosus, and B. punctatus. The masses of G. olivacea, B. speciosus, and B. punctatus were less when they were reared with S. couchii, demonstrating the possible competitive dominance of S. couchii. These results suggest that the competitive ability of S. couchii may play a role in excluding G. olivacea, B. speciosus, and B. punctatus from very ephemeral breeding sites, and that susceptibility to predation could play a role in excluding S. couchii from breeding sites of longer duration that are more likely to be colonized by aquatic predators.     

Ontogenetic trait variation and metacommunity effects influence species relative abundances during tree community assembly

Predicting species abundance is one of the most fundamental pursuits of ecology. Combining the information encoded in functional traits and metacommunities provides a new perspective to predict the abundance of species in communities. We applied a community assembly via trait selection model to predict quadrat-scale species abundances using functional trait variation on ontogenetic stages and metacommunity information for over 490 plant species in a subtropical forest and a lowland tropical forest in Yunnan, China. The relative importance of trait-based selection, mass effects, and stochasticity in shaping local species abundances is evaluated using different null models. We found both mass effects and trait selection contribute to local abundance patterns. Trait selection was detectable at all studied spatial scales (0.04–1 ha), with its strength stronger at larger scales and in the subtropical forest. In contrast, the importance of stochasticity decreased with spatial scale. A significant mass effect of the metacommunity was observed at small spatial scales. Our results indicate that tree community assembly is primarily driven by ontogenetic traits and metacommunity effects. Our findings also demonstrate that including ontogenetic trait variation into predictive frameworks allows ecologists to infer ecological mechanisms operating in community assembly at the individual level.     

Ecosystem engineering and predation: the multi-trophic impact of two ant species

1. Ants are ubiquitous ecosystem engineers and generalist predators and are able to affect ecological communities via both pathways. They are likely to influence any other terrestrial arthropod group either directly or indirectly caused by their high abundance and territoriality. 2. We studied the impact of two ant species common in Central Europe, Myrmica rubra and Lasius niger, on an arthropod community. Colony presence and density of these two ant species were manipulated in a field experiment from the start of ant activity in spring to late summer. 3. The experiment revealed a positive influence of the presence of one ant colony on densities of decomposers, herbivores and parasitoids. However, in the case of herbivores and parasitoids, this effect was reversed in the presence of two colonies. 4. Generally, effects of the two ant species were similar with the exception of their effect on Braconidae parasitoid densities that responded positively to one colony of M. rubra but not of L. niger. 5. Spider density was not affected by ant colony manipulation, but species richness of spiders responded positively to ant presence. This effect was independent of ant colony density, but where two colonies were present, spider richness was significantly greater in plots with two M. rubra colonies than in plots with one colony of each ant species. 6. To test whether the positive ecosystem engineering effects were purely caused by modified properties of the soil, we added in an additional experiment (i) the soil from ant nests (without ants) or (ii) unmodified soil or (iii) ant nests (including ants) to experimental plots. Ant nest soil on its own did not have a significant impact on densities of decomposers, herbivores or predators, which were significantly, and positively, affected by the addition of an intact nest. 7. The results suggest an important role of both ant species in the grassland food web, strongly affecting the densities of decomposers, herbivores and higher trophic levels. We discuss how the relative impact via bottom-up and top-down effects of ants depends on nest density, with a relatively greater top-down predatory impact at higher densities.     

Parametric scaling from species relative abundances to absolute abundances in the computation of biological diversity: a first proposal using Shannon's entropy

Traditional diversity measures such as the Shannon entropy are generally computed from the species' relative abundance vector of a given community to the exclusion of species' absolute abundances. In this paper, I first mention some examples where the total information content associated with a given community may be more adequate than Shannon's average information content for a better understanding of ecosystem functioning. Next, I propose a parametric measure of statistical information that contains both Shannon's entropy and total information content as special cases of this more general function.     

Chaoborus predation and the function of phenotypic variation in Daphnia

To investigate the role of helmet formation in defense against predation, laboratory experiments were used to analyze the effects of morphological changes in Daphnia on susceptibility to Chaoborus predation. Behavioral observations of Chaoborus preying on helmeted and non-helmeted Daphnia suggest pre-contact advantages for helmeted prey but post-contact advantages for non-helmeted prey. Helmeted Daphnia are better at evading capture by Chaoborus but may also be more easily handled by the predator. Swimming behavior of the prey, which is influenced by the presence of a tailspine, may affect Chaoborus strike distance. These results re-emphasize the potential hydromechanical importance of body shape changes in defense against predation.     

Competition and predation models applied to the case of the sibling birds species ofHippolais in Burgundy

We study the case of two sibling species ofHippolais(Aves). Very little differences can be observed in the morphology of both species. The breeding area of these species are complementary. Roughly, one species breeds North and East of Europe (Hippolais icterina) while the other breeds South and West of Europe (Hippolais polyglotta). There exitst a narrow zone of sympatry passing through Burgundy. Since several years, it has been observed that this area of sympatry was moving in the North-East direction at a European scale. This means that progressivelyH. icterina is declining and is replaced byH. polyglotta. Some assumptions can be made in order to explain this evolution, for instance competition or predation. Series of observations concerning the diets of nestlings of both species have been realized. These observations show some differences in the diet compositions. The breeding success of the two species has been studied. Numerical simulations of a competition model taking into account the observed differences between the food types eaten by the two species are presented. These simulations do not explain the regression ofH. icterina. Then, we present numerical simulations of a predation model with one predator attacking the nestlings of both species. These simulations show that with time one of the two preys must extinct. Predation rather than competition seems to be the right explanation.     

Species abundances influence the net biodiversity effect in mixtures of two plant species

Species abundances (evenness or identity of the dominant species in mixtures) usually are not rigorously controlled when testing relationships between plant production and species richness and may be highly dynamic in disturbed or early successional communities. Changes in species abundances may affect the yield of mixtures relative to yields expected from species monocultures [the net biodiversity effect (NBE)] by changing how species that differ in function are distributed in the plant community. To test the prediction that variation in species abundances affects the NBE via changes in the expression of functional differences among species (the complementarity effect), we grew perennial grasses and forbs in field plots in central Texas, USA, as equal-density monocultures and two-species mixtures in which relative abundances of species were varied. Function should differ more consistently between species of different growth forms than of the same growth form. We predicted, therefore, that the complementarity effect and influence of species abundances on the NBE would be more pronounced in grass/forb mixtures than in mixtures with species of the same growth form (grass/grass and forb/forb mixtures). The NBE varied with species evenness in two of the six species pairs studied and with identity of the dominant species in a third species combination. The NBE was sensitive to species proportions in both grass/grass and grass/forb assemblages. In all combinations in which the NBE differed with either evenness or identity of the dominant species, the variation resulted largely from change in the complementarity effect. Our results suggest that the NBE of mixtures is sensitive to effects of species ratios on complementarity.     

Nest predation and nestling growth rate of two lark species in the Negev Desert, Israel

Clutch-size, nestling growth and predation rates on eggs and nestlings in two sympatric alaudids, the Crested Lark Galerida cristata and the Desert Lark Ammomanes deserti, were studied in the Negev desert of Israel. Logistic growth constants were similar for both species, and experimental brood reduction did not accelerate the growth rate of their nestlings. It is suggested that the predation rate on nests of both species has been sufficiently high to select for maximal growth rate of nestlings. Overall probability of predation was 0.85 on a Desert Lark nest and 0.76 on a Crested Lark nest. The smaller clutch-size of the Desert Lark (3.7) may be an adaptation to a higher predation risk, as compared to that of the Crested Lark (4.6) which is more vigilant and nests in more concealed sites.