Negative Interspecific Interactions Research Articles

Reproductive interference determines persistence and exclusion in species interactions

1. Reproductive interference is a negative interspecific sexual interaction that adversely affects the fitness of males and females during reproductive process. Theoretical studies suggest that because reproductive interference is characterized by positive frequency dependence it is far more likely to cause species exclusion than the density dependence of resource competition. However, the respective contributions of resource competition and reproductive interference to species exclusion, which have been frequently observed in many competition studies, remain unclear. 2. We show that reproductive interference is a far more critical cause of species exclusion than resource competition in the competition between Callosobruchus bean weevil species. In competition experiments over several generations, we manipulated the initial relative abundance of the adzuki bean beetle, Callosobruchus chinensis, and the southern cowpea beetle, Callosobruchus maculatus. When the initial adult ratio of C. chinensis : C. maculatus were 6 : 2 and 4 : 4, C. chinensis excluded C. maculatus. However, when C. maculatus was four times more abundant than C. chinensis at the start, we observed the opposite outcome. 3. A behavioural experiment using adults of the two species revealed asymmetric reproductive interference. The fecundity and longevity of C. maculatus females, but not those of C. chinensis females, decreased when the females were kept with heterospecific males. Fecundities of females of both species decreased as the number of heterospecific males increased. In contrast, resource competition at the larval stage resulted in higher survival of C. maculatus than of C. chinensis. 4. These results suggest that the positive frequency-dependent effect of reproductive interference resulted in species exclusion, depending on the initial population ratio of the two species, and the asymmetry of the interference resulted in C. chinensis being dominant in this study, as in previous studies. Classical competition studies should be reviewed in light of this evidence for reproductive interference.

Bat assemblages on Neotropical land‐bridge islands: nested subsets and null model analyses of species co‐occurrence patterns

ABSTRACTA fundamental goal of ecology is to understand whether ecological communities are structured according to general assembly rules or are essentially dictated by random processes. In the context of fragmentation, understanding assembly patterns and their mechanistic basis also has important implications for conservation. Using distribution data of 20 bat species collected on 11 islands in Gatún Lake, Panama, we tested for non‐randomness in presence–absence matrices with respect to nestedness and negative species co‐occurrence. We examined the causal basis for the observed patterns and conducted separate analyses for the entire assemblage and for various species submatrices reflecting differences in species’ trophic position and mobility. Furthermore, we explored the influence of weighting factors (area, isolation, abundance) on co‐occurrence analyses. Unweighted analyses revealed a significant negative co‐occurrence pattern for the entire assemblage and for phytophagous bats alone. Weighting analyses by isolation retained a pattern of species segregation for the whole assemblage but nullified the non‐random structure for phytophagous bats and suggested negative associations for animalivores and species with low mobility. Area‐ and abundance‐weighted analyses always indicated random structuring. Bat distributions followed a nested subset structure across islands, regardless of whether all species or different submatrices were analysed. Nestedness was in all cases unrelated to island area but weakly correlated with island isolation for incidence matrices of all species, phytophagous bats, and mobile species. Overall, evidence for negative interspecific interactions indicative of competitive effects was weak, corroborating previous studies based on ecomorphological analyses. Our findings indicate that bat assemblages on our study islands are most strongly shaped by isolation effects and species’ differential movement and colonization ability. From a conservation viewpoint this suggests that even in systems with high fragment–matrix contrast, a purely area‐based approach may be inadequate, and structural and functional connectivity among patches are important to consider in reserve planning.

Interspecific and intraspecific interactions in the monogenean communities of fish: a question of study scale?

Monogenean communities of fish have generally been considered non-interactive as negative interspecific interactions have rarely been reported. Most of the earlier studies on monogenean communities, however, have been conducted not only in systems with relatively low parasite abundances but, more importantly, at study scales where microhabitat-level interactions between the parasites are easily overlooked. We examined the communities of 3 abundant Dactylogyrus (Monogenea) species on the gills of crucian carp (Carassius carassius) by analysing the interactions at the scale of individual gill filaments, where interactions between the species, if any, should most likely take place. Contrary to our expectations, we did not find evidence for competitive exclusion between the species, which suggests that monogenean communities are non-interactive even in high parasite abundances. At the species level, individual parasites were highly aggregated within the filaments, essentially showing a strong tendency to occur at either end of a filament. This, together with the result of differences in the distribution of juvenile parasites within the filaments compared to adults, suggests that these parasites are able to actively seek out their conspecifics in small-scale microhabitats during maturation, which again could enhance their mate-finding.

SPATIAL DISTRIBUTIONS OF TWO SPECIES OF MONOGENEANS ON THE GILLS OF SIGANUS FUSCESCENS (HOUTTUYN) AND THEIR SEASONAL DYNAMICS IN CAGED VERSUS WILD-CAUGHT HOSTS

Two monogeneans species, Polylabris mamaevi Ogawa & Egusa, 1980 and Tetrancistrum nebulosi Young, 1967, are sympatric on the gills of Siganus fuscescens (Houttugn, 1782) in the South China Sea. An investigation into their distribution on the host's gills based on monthly samples from both wild and caged populations revealed that these 2 species co-occurred on the same gill arches, but they were segregated. P. mamaevi attached to the distal half of the gill filaments, whereas T. nebulosi attached to the proximal half. This difference may partly be attributed to microhabitat specialization. Microhabitat distributions were intensity dependent for both species. As intensity increased, monogeneans were increasingly found on the second, third, and even fourth gill arches, and niche breadths increased. The changes in distribution and niche breadths at the host gill arch level in relation to differences in host size and sampling period were considered to represent a functional response to increased intensity. Differences in host resources, in either net-caged or wild populations, did not significantly influence the parasite distributions at the host gill arch level. Simultaneous infections of these 2 species were common, but there was no evidence of negative interspecific interactions.

Aggregation and species coexistence in fleas parasitic on small mammals

The aggregation model of coexistence states that species coexistence is facilitated if interspecific aggregation is reduced relative to intraspecific aggregation. We investigated the relationship between intraspecific and interspecific aggregation in 17 component communities (the flea assemblage of a host population) of fleas parasitic on small mammals and hypothesized that interspecific interactions should be reduced relative to intraspecific interactions, facilitating species coexistence. We predicted that the reduction of the level of interspecific aggregation in relation to the level of intraspecific aggregation would be positively correlated with total flea abundance and species richness of flea assemblages. We also expected that the higher degree of facilitation of flea coexistence would be affected by host parameters such as body mass, basal metabolic rate (BMR) and depth and complexity of burrows. Results of this study supported the aggregation model of coexistence and demonstrated that, in general, a) conspecific fleas were aggregated across their hosts; b) flea assemblages were not dominated by negative interspecific interactions; and c) the level of interspecific aggregation in flea assemblages was reduced in relation to the level of intraspecific aggregation. Intraspecific aggregation tended to be correlated positively to body mass, burrow complexity and mass‐independent BMR of a host. Positive interspecific associations of fleas tended to occur more frequently in species‐rich flea assemblages and/or in larger hosts possessing deep complex burrows. Intraspecific aggregation increased relative to interspecific aggregation when species richness of flea infracommunities (the flea assemblage of a host individual) and component communities increased. We conclude that the pattern of flea coexistence is related both to the structure of flea communities and affinities of host species.

Insect gladiators II: Competitive interactions within and between bethylid parasitoid species of the coffee berry borer, Hypothenemus hampei (Coleoptera: Scolytidae)

The coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae) causes substantial reductions in coffee production. It originates from Africa but is now present in almost all of the major coffee producing countries. Classical biological control attempts around the world, including South and Central America, the Caribbean, Indian sub-continent, Indonesia, and Polynesia, including introductions of the African bethylid wasps Prorops nasuta Waterston and Cephalonomia stephanoderis Betrem, have not yet proved sufficiently successful. In Mexico, a bethylid wasp indigenous to North America and Europe, Cephalonomia hyalinipennis Ashmead, has naturally started to attack the borer. The presence of multiple species of natural enemies has the potential to disrupt biological control via negative interspecific interactions. We evaluate both inter- and intraspecific competition among these three bethylids in the laboratory, focussing on pairs of adult females competing directly for hosts. In interspecific contests, the loser is frequently killed. C. stephanoderis is the most successful species, while P. nasuta females never killed their opponents. Intraspecific interactions often involved fighting behavior but were non-fatal. We discuss the implications of the differing strengths of such inter- and intraspecific interactions for the coexistence of these natural enemies of the coffee berry borer and for biological control.

The interplay of positive and negative species interactions across an environmental gradient: insights from an individual-based simulation model

Positive interspecific interactions are commonplace, and in recent years ecologists have begun to realize how important they can be in determining community and ecosystem dynamics. It has been predicted that net positive interactions are likely to occur in environments characterized by high abiotic stress. Although empirical field studies have started to support these predictions, little theoretical work has been carried out on the dynamic nature of these effects and their consequences for community structure. We use a simple patch-occupancy model to simulate the dynamics of a pair of species living on an environmental gradient. Each of the species can exist as either a mutualist or a cheater. The results confirm the prediction: a band of mutualists tends to occur in environmental conditions beyond the limits of the cheaters. The region between mutualists and cheaters is interesting: population density here is low. Mutualists periodically occupy this area, but are displaced by cheaters, who themselves go extinct in the absence of the mutualists. Furthermore, the existence of mutualists extends the area occupied by the cheaters, essentially increasing their realized niche. Our approach has considerable potential for improving our understanding of the balance between positive and negative interspecific interactions and for predicting the probable impacts of habitat loss and climate change on communities dominated by positive interspecific interactions.

Mechanisms responsible for the positive diversity–productivity relationship in Minnesota grasslands

AbstractSpecies’ extinctions have spurred debate on whether interactions among few or among many species cause a positive diversity–productivity relationship in experimentally assembled grasslands. We addressed this question by quantifying the productivity of 14 species across an experimental diversity gradient in Minnesota. We found that interspecific interactions leading to coexistence and competitive displacement both determine which species overyield; i.e. are more productive at high diversity. Overyielding species were either superior N competitors (C4 grasses) or N fixers (legumes). Surprisingly, these species were not most productive in monoculture, thus, the ‘selection’ of productive species in diverse plots did not cause the positive diversity–productivity relationship. Both positive (with legumes) and negative interspecific interactions (with C4 grasses) determined whether individual species overyielded. Foliar pathogens did not cause overyielding, although other natural enemies may be responsible. Overyielding species are not displacing underyielding species over time, implying that other diversity‐promoting interactions also operate in this experiment.

Ontogenetic shifts in competitive interactions and intra‐guild predation between two wolf spider species

Abstract.1. The wolf spiders (Araneae: Lycosidae)Hogna helluo(Walckenaer) andPardosa milvinaHentz co‐occur in soybean fields of south‐west Ohio, U.S.A. As adults,Hognais the larger species and has the competitive advantage in most interactions; due to differing phenologies, however, their size‐classes frequently overlap and as such there is potential for shifts in competitive ability and intra‐guild predation. The hypothesis that competitive interactions and intra‐guild predation will favourPardosawhenPardosais similar‐sized, or has a size advantage overHogna, was tested in laboratory and field experiments.2. Studies in laboratory arenas, pairing similar‐sized individuals of these species andHognaspiderlings with larger spiders of both species, revealed that intra‐guild predation seldom occurs with similar‐sizedHognaandPardosa, howeverPardosawill consume smallHognaindividuals in laboratory arenas.3. Field experiments involved stocking high densities (50 m–2) ofPardosaandHognain enclosures placed in soybean fields. In experiments with spiders of similar size, no interspecific effects were uncovered, but an intraspecific effect was found forPardosaas its survival and weight gain were lower in the presence of more conspecifics. LargeHognaorPardosahad no effect on the survival or weight gain ofHognaspiderlings.4. AlthoughHognais a better competitor as an adult, it has no advantage overPardosawhen their size‐classes overlap, andPardosaeffects onHognamay be inconsequential under field conditions. Therefore, the co‐existence of these species is fostered by the fact that there are few negative interspecific interactions during their ontogeny.

Water temperature influencing dactylogyrid species communities in roach, Rutilus rutilus, in the Czech Republic

Dactylogyrid species (Monogenea) communities were studied in roach, Rutilus rutilus, collected from two localities in the basin of Morava river, Czech Republic, during the period from April to November 1997 and March to September 1998 to determine the effect of water temperature on parasite abundance, species richness and diversity. Dactylogyrid species were found to co-occur on the gills of roach with up to six species found on the same host individual. Nine dactylogyrid species were identified with the abundance of each reaching a very low level. Niche size was considered to increase with species abundance even when water temperature was high. There was a strong effect of water temperature on abundance of the common dactylogyrid species (D. crucifer, D. nanus, D. rutili and D. suecicus) as well as of the rare species D. rarissimus. The temporary occurrence of the rare species was found without any temperature effect. Water temperature did not affect the relationship between abundance and niche size. Niche size increased with abundance, even when the water temperature was high, which suggests that negative interspecific interactions are not important within dactylogyrid communities.

Water temperature influencing dactylogyrid species communities in roach, Rutilus rutilus, in the Czech Republic

Dactylogyrid species (Monogenea) communities were studied in roach, Rutilus rutilus, collected from two localities in the basin of Morava river, Czech Republic, during the period from April to November 1997 and March to September 1998 to determine the effect of water temperature on parasite abundance, species richness and diversity. Dactylogyrid species were found to co-occur on the gills of roach with up to six species found on the same host individual. Nine dactylogyrid species were identified with the abundance of each reaching a very low level. Niche size was considered to increase with species abundance even when water temperature was high. There was a strong effect of water temperature on abundance of the common dactylogyrid species (D. crucifer, D. nanus, D. rutili and D. suecicus) as well as of the rare species D. rarissimus. The temporary occurrence of the rare species was found without any temperature effect. Water temperature did not affect the relationship between abundance and niche size. Niche size increased with abundance, even when the water temperature was high, which suggests that negative interspecific interactions are not important within dactylogyrid communities.

A perspective on the ecology of trematode communities in snails.

This paper presents a perspective on the ecology of trematodes in snail hosts based on recent evidence. Because flukes use snails almost obligatorily as first intermediate hosts, we highlight the role of gastropods as keystone species for trematodes and their communities. After reviewing recent developments in the transmission of trematodes to and from snails, we discuss trematode communities within individual snails (infracommunities) and in snail populations (component communities). Results garnered using various protocols at the infracommunity level are reviewed. The few data available, all from marine systems, indicate that low colonization rates characterize infracommunities, suggesting that trematode infracommunities tend to be isolationist in character rather than interactive. The variety of trematode species present in a component community seems to be determined by spatial overlap of definitive hosts. Relative abundance of species in a component community shows little dependence on negative interspecific interactions at the level of the infracommunity. Temporal aspects of trematode communities are related to the life history of the host snail. The component communities of long-lived snails (mostly marine) integrate many infection episodes whereas shorter-lived snails (mostly freshwater) acquire new component communities each time host cohorts turnover.

Hematozoa of hatch-year common mergansers from Michigan.

Fifty-five hatch-year common mergansers (Mergus merganser) were sampled for hematozoa from Douglas Lake (Michigan, USA) on 17 July 1995. Forty-one (75%) were infected with hematozoa. Haemoproteus greineri and Leucocytozoon simondi were common, infecting 28 (51%) and 26 (47%) common mergansers, respectively. Plasmodium circumflexum infected two (4%) birds. The common merganser is a new host record for H. greineri and P. circumflexum. Intensity data indicate possible negative interspecific interaction between H. greineri and L. simondi.

Mechanisms of Maintenance of Species Diversity

▪ Abstract The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence, in which species diversity slowly decays over time, have focused almost exclusively on equalizing mechanisms. These models would be more robust if they also included stabilizing mechanisms, which arise in many and varied ways but need not be adequate for full stability of a system. Models of unstable coexistence invite a broader view of diversity maintenance incorporating species turnover.

Parasite community study of the undulate ray Raja undulata in the Rı́a of Muros (Galicia, northwest Spain)

The parasites present in 75 undulate rays ( Raja undulata Lacepède, 1802) captured in the Rı́a of Muros, a coastal embayment (rı́a) in northwest Spain were studied. A total of five species of cestodes ( Onchobothrium uncinatum, Phyllobothrium lactuca, Echeneibothrium beauchampi, Acanthobothrium benedeni and Grillotia sp.), three species of nematodes ( Schulmanela [ Piscicapillaria] sp., Pseudanisakis rotundata and Cystidicolidae gen. sp.) and one acanthocephalan ( Acanthocephaloides propinquus) were detected. All species were elasmobranch-specific except Cystidicolidae sp. and Acan. propinquus, which can both be considered accidental in this host. Species diversity peaked over the period April–September (Shannon–Wiener diversity=1.9–2.2; Pielou evenness=0.8–0.9). The dominant species were cestodes, notably O. uncinatum (present in 73 of the 75 hosts, and accounting for 45% of all parasites detected), followed by A. benedeni, P. lactuca and Grillotia sp., all of which were present in more than 30% of the host individuals. All species detected were autogenous, and all individuals except those of Cystidicolidae gen. sp. were adults. The five species of cestodes were present in hosts of all sizes, though single-host species richness, single-host species diversity and overall intensity of infection increased with increasing host size. Nematodes appeared in larger individuals (body length >33 cm). Larval Cystidicolidae gen. sp. appeared only in the largest size class (>43 cm), probably because only rays of this size are capable of ingesting relatively large demersal fish, the usual intermediate hosts in this area. Analysis of the species compositions of single-host parasite communities, considering cestodes only, suggests that negative interspecific interactions do not occur, despite the typically large size and abundance of the parasites, and their spatial concentration in the spiral valve.

Larval Trematode Assemblages in the Snail Lymnaea stagnalis from Southeastern Wisconsin

From May through November 1993 and 1994, Lymnaea stagnalis appressa were collected from a stream adjacent to Cedarburg Bog, Ozaukee County, Wisconsin. Observations of cercarial shedding and subsequent dissection of snails revealed a relatively depauperate digenean component community consisting primarily of 3 common species. The most frequently occurring form was the metacercaria of Cotylurus flabelliformis. Sporocysts and cercariae of this species were rarely observed. Snails also harbored sporocysts and shed cercariae of Schistosomatium douthitti and a plagiorchid. Seasonal and yearly dynamics of the component trematode community reflect the apparent inability of sporocysts to overwinter in snails at this location. They also seem to be associated closely with snail life histories in terms of the availability of large snails, most often infected by the sporocysts of S. douthitti and the plagiorchid. Analyses of double infections revealed the occurrence of a negative interspecific interaction between the tetracotyles of C. flabelliformis and sporocysts of S. douthitti. Other combinations of trematode species did not reveal negative interactions. Competition does not seem to play a major role in the structure of the component community at this location.

Factors controlling the distribution of Marenzelleria cf. viridis, Pygospio elegans and Streblospio shrubsoli (Polychaeta: Spionidae) in the southern Baltic Sea, with special attention for the response to an event of hypoxia

The large-scale distribution patterns of the estuarine spionid polychaetes Marenzelleria cf. viridis, Pygospio elegans, and Streblospio shrubsoli were studied in the Pomeranian Bay (southern Baltic Sea) at 20 stations in April 1993 and their relationship with hydrographic factors and sediment composition investigated. The densities of M. cf. viridis and S. shrubsoli decreased rapidly with increasing distance offshore. A corresponding decrease in phytoplankton concentration offshore is suggested as the main cause for the observed spatial patterns. P. elegans was more evenly distributed. At 10 selected stations further samples were collected between April 1993 and July 1996 to study the response of abundance and biomass of the three polychaetes to changes in environmental conditions and to investigate interspecific interactions within the macrofauna. Salinity, pelagic food supply, and sediment parameters did not change. At three of these stations redox potential of the sediment and macrofauna composition were affected by an unusual hypoxic/anoxic event in July/August 1994. All three spionid species were able to survive moderate seasonal hypoxic conditions, but died after exposure to severe anoxia. Special attention was focused on the re-establishment of the spionids. The rate with which M. cf. viridis and P. elegans re-colonised defaunated stations varied between a few weeks and two years. These differences in rate of re-establishment were attributed to the distance from undisturbed recruitment areas, and to the severity of the oxygen deficiency. Increasing densities of P. elegans and S. shrubsoli after the hypoxic event coincided with a reduced abundance of the bivalve Mya arenaria, suggesting a negative interspecific interaction.

Effects of Steelhead Density on Growth of Coho Salmon in a Small Coastal California Stream

Weight change in age-0 coho salmon Oncorhynchus kisutch at about natural density was negatively related to the density of juvenile steelhead (anadromous rainbow trout O. mykiss) in a 6-week experiment conducted in July–August 1993 in the north and south forks of Caspar Creek, California. The experiment used 12 enclosed stream sections, each containing a pool and a portion of upstream riffle, with two replicates of three steelhead densities—zero, natural density (1×), and twice the natural density (2×)—on both the north and south forks. The natural density of coho salmon was about one-sixth the density of steelhead. Coho salmon survival was high (87% overall) and not related to treatments. In the north fork, coho salmon weight change was positive in zero density steelhead treatments, zero in 1× treatments, and negative in 2× treatments. Coho salmon weight change in the south fork was less favorable than in the north fork but was also negatively related to the density of steelhead. These results indicate that under some conditions resource partitioning by salmonid species does not eliminate negative interspecific interactions.

Community organization in a recently assembled fauna: the case of Polynesian ants.

The ant species inhabiting three remote Polynesian islands were censused by hand collecting techniques. Three commonly occurring species, which exhibited complementary distribution patterns, were numerically and behaviorally dominant to other species in the communities in which they occurred. Field observations and laboratory experiments showed that negative interspecific interactions were important in maintaining the exclusive territories of the dominant species. Habitat also played a role in determining the distribution of dominant species. Pairwise tests of association among all species revealed dominant species were commonly positively associated with their own non-overlapping group of subordinate species, forming a large-scale mosaic distribution pattern of dominant and subordinate species. Baiting experiments, conducted with and without the dominant species removed, demonstrated that the presence of the dominant species decreased: (1) the proportion of baits occupied by other species, and (2) overall ant species diversity, at rich food resources. In ant communities where one of the three recognized dominant species was present, the outcome of negative interspecific interactions among species was more predictable than in communities without a recognized dominant. The same patterns were evident regardless of which of the three dominant species was present in the community. These patterns of community organization observed in this relatively newly assembled fauna are very similar to those reported from studies of older ant communities in mainland areas.

IS DECREASED FREQUENCY OF MATING AMONG CONSPECIFICS A COST OF SYMPATRY IN SALAMANDERS?

Reproductive interactions among species in areas of and contact zones have long fascinated evolutionary biologists. Much interest and fierce debate has centered on the potential for natural selection to prevent interspecific mating between species in cases in which the progeny from such unions exhibit reduced fitness (see papers in Otte and Endler 1989). The potential risk of interspecific mating may be regarded as an important cost of sympatry for many species. Other reproductive costs of may exist even for species that are sexually incompatible and thus never engage in interspecific mating. For example, individuals of different species may use similar resources necessary for successful mating. In odonates, this may result in lost mating opportunities with conspecifics because of courtship misdirected toward heterospecific females (Singer 1990). Negative interspecific interactions also may arise during the process of mate attraction in the form of signal interference, an unintended by-product of two or more species broadcasting signals in the same sensory modality while in close physical proximity. Anuran choruses are prime examples of situations in which interspecific acoustic interference may result in a decreased probability of encounters between conspecifics (e.g., Schwartz and Wells 1983). Levels of sexual incompatibility typically are high among sympatric species of plethodontid salamanders ofthe genus Desmognathus, and thus the risk of interspecific mating probably is not a reproductive cost of for contemporary populations (Maksymovitch and Verrell 1993). Nevertheless, the presence of a heterospecific individual could still exert a negative influence on