Intraspecific Competition For Space Research Articles

Disadvantages of living in a populous neighborhood for sit‐and‐wait predators: Competition for space reduces pit‐trap size in antlion larvae

AbstractThe study of how trap design responds to biotic and abiotic conditions can help to understand the selective forces affecting the foraging of trap‐building organisms. We experimentally tested whether pit design can be modified by intraspecific competition for space in larvae of Myrmeleon crudelis, a common sit‐and‐wait predator that digs conical pit traps in the soil to capture walking arthropods. In a tropical forest in Costa Rica, we measured pit dimensions, larval body size, and the level of competition (i.e., density of neighboring traps) in 40 antlion larvae. These larvae were then taken to the laboratory and allowed to build new traps in individual containers. We measured within‐individual changes in the size of traps in the field and in the laboratory, and related these to the level of competition experienced in the field. Larvae with relatively high levels of competition in the field showed a greater increase in the size of their pits in the laboratory. This change was independent of larval size. Larvae with none or few neighbors in the field showed little change in their pit sizes, whereas those with higher competition levels increased their diameter and depth up to 1,400% and 1,000%, respectively. Our results demonstrate that, at least in high‐density aggregations, pit design is restricted by competition in addition to the constraints imposed by body size. This work suggests that biotic interactions can play a role in the design of extended phenotypes in sit‐and‐wait predators that live in dense aggregations.

Aggregation and negative interactions in low-diversity and unsaturated monogenean (Platyhelminthes) communities in Astyanax aeneus (Teleostei) populations in a neotropical river of Mexico.

We studied monogenean communities of 11 populations of Astyanax aeneus (Günther) separated by small geographical distances along 60 km of the Lacantún river in Chiapas, Mexico, in February and August 2012. We found 12 monogenean taxa. Amongst these, five species specialist for Astyanax were widely distributed regionally, constituting 90% of the total collected monogeneans, with one of these species dominating most component communities. The high similarities in terms of composition between the component communities (SJaccard > 60%) as well as in terms of the abundance and composition between infracommunities (SBray Curtis > 40%), provide empirical evidence that transmission, both between hosts at the same location and between component communities, is high and effective. No resemblance pattern was detected between locations in terms of their spatial distribution. The composition of these communities was spatially and temporally consistent over the two very different weather periods sampled. These communities were not saturated. Our analysis suggests that the potential richness of the infracommunities is proportional to the number of monogenean species available in the component community. We found aggregation in the populations and between monogenean species. Intraspecific aggregation is density dependent, suggesting that intraspecific competition for space is not a limiting factor for the development of the population. We evaluated the associations for each species pair and detected 77% negative interactions (134/177 associations), suggesting that interspecific competition plays an important role in shaping these communities. The negative correlations of abundance between pairs of species contributes to confirmation of competition. Intraspecific aggregation increased relative to interspecific aggregation with richness in the component community, facilitating coexistence of the species. Our results suggest that these are interactive communities, where monogeneans disperse efficiently from a common source, colonize patches (hosts) together, and compete with other species even at low population densities. Finally, the coexistence of these species is favored by the unpredictable recruitment and aggregated use of fragmented resources.

Spatial point patterns of Antarctic krill fishery in the northern Antarctic Peninsula

As a key species in the Antarctic ecosystem, the spatial distribution of Antarctic krill (thereafter krill) often tends to present aggregation characteristics, which therefore reflects the spatial patterns of krill fishing operation. Based on the fishing data collected from Chinese krill fishing vessels, of which vessel A was professional krill fishing vessel and Vessel B was a fishing vessel which shifted between Chilean jack mackerel (Trachurus murphyi) fishing ground and krill fishing ground. In order to explore the characteristics of spatial distribution pattern and their ecological effects of two obvious different fishing fleets under a high and low nominal catch per unit effort (CPUE), from the viewpoint of spatial point pattern, the present study analyzed the spatial distribution characteristics of krill fishery in the northern Antarctic Peninsula from three aspects: (1) the two vessels' point pattern characteristics of higher CPUEs and lower CPUEs at different scales; (2) correlation of the bivariate point patterns between these points of higher CPUE and lower CPUE; and (3) correlation patterns of CPUE. Under the analysis derived from the Ripley's L function and mark correlation function, the results showed that the point patterns of the higher/lo-wer catch available were similar, both showing an aggregation distribution in this study windows at all scale levels. The aggregation intensity of krill fishing was nearly maximum at 15 km spatial scale, and kept stably higher values at the scale of 15-50 km. The aggregation intensity of krill fishery point patterns could be described in order as higher CPUE of vessel A > lower CPUE of vessel B >higher CPUE of vessel B > higher CPUE of vessel B. The relationship of the higher and lo-wer CPUEs of vessel A showed positive correlation at the spatial scale of 0-75 km, and presented stochastic relationship after 75 km scale, whereas vessel B showed positive correlation at all spatial scales. The point events of higher and lower CPUEs were synchronized, showing significant correlations at most of spatial scales because of the dynamics nature and complex of krill aggregation patterns. The distribution of vessel A's CPUEs was positively correlated at scales of 0-44 km, but negatively correlated at the scales of 44-80 km. The distribution of vessel B's CPUEs was negatively correlated at the scales of 50-70 km, but no significant correlations were found at other scales. The CPUE mark point patterns showed a negative correlation, which indicated that intraspecific competition for space and prey was significant. There were significant differences in spatial point pattern distribution between vessel A with higher fishing capacity and vessel B with lower fishing capacity. The results showed that the professional krill fishing vessel is suitable to conduct the analysis of spatial point pattern and scientific fishery survey.

Territoriality in females of the slender opossum (Marmosops paulensis) in the Atlantic forest of Brazil

Spatial organization within animal populations is often thought to reflect the outcome of strategies implemented by each individual to enhance its reproductive success and survival (Clutton-Brock 1989). Thus, while females usually focus on the acquisition of food and breeding sites, male dispersion is more often determined by the distribution and availability of females (Clutton-Brock 1989). Due to these factors, intraspecific competition for space could lead to the adoption of a territorial strategy, whenever the benefits of territorial defence are higher than the costs (Brown & Orians 1970). Among small mammals, two main hypotheses have been proposed to explain the occurrence of territoriality in females. Ostfeld (1990) proposed that females should defend food resources, so the distribution and availability of food items should determine the cost–benefit relationship of adopting a territorial strategy. However, Wolff (1993) developed a hypothesis, based on small rodents, that females should defend nest sites in order to avoid infanticide, the so-called pup-defence hypothesis.

Maternal and birth colony effects on survival of Weddell seal offspring from McMurdo Sound, Antarctica

1. Maternal and birth colony effects on offspring survival to weaning and to reproductive age were examined for Weddell seals using mark–recapture models and over 25 years of mark–resight data from McMurdo Sound, Antarctica. 2. Pre‐weaning mortality (proportion of the total pups found dead on the ice surface) varied significantly with maternal age and was significantly higher for primiparous mothers than for multiparous mothers. 3. Offspring survival to reproductive age also increased significantly with maternal age and experience. Survival of offspring from birth to 6 years of age increased significantly with maternal body length only for male offspring. 4. Increased survivorship of offspring with maternal age was only evident for offspring of multiparous (rather than primiparous) mothers. This suggests that the age when mothers have their first pup may not affect survival of offspring, although lack of effect of age on offspring survival for primiparous mothers may be due to insufficient variation in age of first reproduction in our sample for us to detect a trend. 5. Pre‐weaning survival of offspring also varied significantly among pupping colonies. In 1983, a year of low reproduction and low first‐year survival for the McMurdo population (Testa 1987b; Hastings 1996), first‐year survival was lower for offspring born in Outer Erebus Bay (west of 166·7°E) than for offspring born in Inner Erebus Bay (east of 166·7°E). 6. Maternal effects on offspring survival may be related to quality of breeding site. Maternal age and experience varied significantly among pupping colonies. That pup population size was stable at all colonies over the study period suggests non‐random age‐distribution of mothers may not be an artefact of population growth, but instead result from intraspecific competition for space in good pupping colonies. 7. Offspring survival, pup population size, and mean maternal age at colonies were significantly positively correlated. This suggests that favourable environmental conditions and high maternal or paternal quality may interact to enhance survival of offspring at larger colonies.

Intrathalline and size‐dependent patterns of activity in Lasallia pustulata and their possible consequences for competitive interactions

1. In dense populations of the saxicolous lichen Lasallia pustulata the margins of adjacent thalli overlap each other in intraspecific competition for space and light. 2. In situ non‐destructive monitoring of hydration‐dependent potential photosynthetic activity by modulated fluorescence systems in different parts of the thallus shows that the activity is structured by a centre‐to‐margin gradient, with the centre of the thallus remaining active for substantially longer periods than the margins when the thalli dry up after being activated by wetting. The pattern reflects the water status of different parts of the thallus; the margins which are thin and exposed dry up first. 3. The activity pattern within individual lichen thalli suggests that marginal overlapping between neighbours may have a less detrimental effect on the shadowed individuals than expected from a pure consideration of the amount of area shadowed. Because the centre of the lichen thallus is active for longer periods, shadowing of this region may possibly be more harmful per area unit than an overlap at the less active margins. 4. Larger thalli are active for substantially longer periods than small ones. Even the margins of larger thalli tend to be active for a longer period than the centre of small thalli.

Inducible aggression and intraspecific competition for space in a marine bryozoan, Membranipora membranacea

We experimentally investigated the causes and consequences of stolon production in the marine bryozoan Membranipora membranacea. Inducible stolons appear to mediate contests for space among conspecifics by slowing the growth of adjacent competitors. However, because stolons are produced in some but not all competitive interactions, we examined whether environmental factors such as food and hydrodynamic regime regulate their production. Furthermore, because stolons are ephemeral, persisting for only 24 h, we removed stolons to determine whether stolon production affected the outcome of competitive contests. Removing stolons from large colonies reduced their ability to surround a small neighbor, but increased their growth rate. Control colonies, producing their full complement of stolons, grew more slowly than colonies with stolons removed, suggesting that there is a tradeoff between stolon production and growth. The rate of stolon production was higher in colonies grown under lower food conditions. The likelihood that waterborne chemical or hydrodynamic cues induce stolon formation is diminished by our finding that the frequency of stolon production was unaffected by the relative positions of two interacting colonies in unidirectional flow.

Life Table and Key Factor Studies of Ctenarytaina thysanura Ferris and Klyver (Hemiptera: Psyllidae) on Boronia megastigma Nees. ex Bartl. (Rutaceae) in Tasmania

ABSTRACTThe psyllid pest Ctenarytaina thysanura was studied intensively in Tasmania, Australia for nine generations from 1986 to 1989, and the identification and quantification of different mortality factors determined by key factor analysis. the analysis identified mortalities of late stage nymphs as key factors influencing C. thysanura populations. Simple graphical analysis suggested that the more predators and parasitoids there are per prey individual the higher the relative prey mortality and that predators and parasitoids acted as regulating agents at low psyllid densities but once the psyllid attained higher densities the negative feedback regulating effect is disengaged. the predators and parasitoids acted in a delayed density dependent manner with a negative feedback delay of two generations. In the absence of these agencies, through indiscriminate spraying, psyllid numbers increased significantly to be ultimately limited by an absence of the essential resource, the terminal shoot. Intraspecific competition for space and food during host plant deterioration resulted in reduction of size and emigration of adult psyllids.

Lissarca notorcadensis (Bivalvia: Philobryidae) living on Notocidaris sp. (Echinoidea: Cidaridae): Population dynamics in limited space

Population dynamics of the epizoic bivalve Lissarca notorcadensis living on spines of cidaroid sea urchins in the Weddell Sea were investigated. Total production (somatic & gonad) of the suspension feeding bivalve ranged between 16.5 and 487.4 mg AFDM y−1 per sea urchin. Annual sedimentation rates are not sufficient to maintain the production of the Lissarca sub-populations carried by the sea urchins, and resuspension of organic matter is most likely to be an important food source. The ratio of the number of freshly settled juveniles to the number of embryos brooded is between 0.054 and 0.207 and seems negatively related to the biomass already present, indicating intraspecific competition for space. Interspecific competition for space is caused by the strong preference of L. notorcadensis as well as other epizoa (colonial anthozoans and bryozoans) for the spines located on the aboral hemispere of the sea urchins.

Effect of food supply and body size on the foraging behavior of the burrowing sea urchin Echinometra mathaei (de Blainville)

The foraging behavior of the normally sedentary sea urchin Echinometra mathaei (de Blainville) from Hawaii was examined in the laboratory. Sea urchins, living in cavities in limestone rocks, were divided into two treatments: in one the animals were fed daily and in the other they were starved for a 34-day period. The frequency of foraging of sea urchins in each treatment and in three size classes was determined. Starved sea urchins increased their foraging behavior while fed animals remained sedentary. Intermediate-sized animals were most inclined to forage for food. Under laboratory conditions, E. mathaei maintained a sedentary mode of feeding as long as drift food was available but began to forage when starved. Size-related differences in foraging were observed and may be related to factors such as differing food requirements, susceptibility to predation and intraspecific competition for space.

Predicted Evolutionary Response to Selection for Tolerance of Soybean (Glycine max) and Intraspecific Competition in a Nonweed Population of Poorjoe (Diodia teres)

Genetic variation within a nonweed (coastal) population of poorjoe was measured in an experimental population subjected to soybean and intraspecific competition for space and light. A sib analysis was used to estimate phenotypic and genetic variance/covariance components of aboveground biomass production and five independent measurements of growth defined by a path-coefficient model. A multivariate analysis of response to selection was applied to predict evolutionary change in the growth measurements in response to selection for performance under soybean and intraspecific space/light competition; sufficient genetic variation was present in the experimental population to allow a rapid response to this selection. Selection under competitive conditions was predicted to cause the nonweed population to emerge earlier, grow faster early in development, change in growth form, and grow faster under a soybean canopy. Most of these changes would increase the resemblance of the selected population to a weed population of poorjoe. However, the growth rate of the selected population under a soybean canopy was predicted to become greater than that actually observed in the present-day weed population. Multivariate analysis of response to selection may be generally useful in predicting evolutionary response of plant pest populations to control practices.

The measurement of hunger as a relative estimate of food available to populations of Nassarius pauperatus.

It is often difficult to estimate the amount of food available to an animal population, especially for species having unspecialised diets. The intertidal snail Nassarius pauperatus is omnivorous, feeding on both algae and animal carrion. Sampling the standing crops of carrion and algae was not thought to be a valid measure of the amount of food available to N. pauperatus. Instead, food availability was estimated indirectly, by measuring how hungry snails were.The percentage of snails feeding within 15 min of having been offered a meal of the bivalve Katelysia scalarina (Lamarck) was found to be a realiable and comparative estimate of food availability, and was measured in the field at 17 locations. The mean length of adult Nassarius pauperatus was negatively correlated with hunger, and at locations having high indices of hunger there was evidence of intraspecific competition for space to feed around items of carrion.These results are discussed and it is proposed that Nassarius pauperatus are surrounded by algal food of poor quality, with carrion being an important part of their diet for survival, growth and reproduction.

A field study of settlement behaviour inBalanus balanoidesandElminius modestus(Cirripedia: Crustacea) in relation to competition between them

There can be little doubt that competition for space, both inter- and intraspecific is a major factor in barnacle ecology. Southward & Crisp (1956) first pointed out the role of competition betweenBalanus balanoides(L.) andChthamalus stellatus(Poli) in south-west Britain which Connell (1959, 1961) later demonstrated experimentally. Crisp (1958) discussed competition between the indigenousB. balanoidesand the immigrantElminius modestusDarwin in the intertidal zone, and measurements of growth rates, using manipulated populations of these two species, indicated that inter- and intraspecific competition for space after settlement is intense (Crisp, 1964).

Factors Regulating the Distribution and Population Dynamics of the Amphipod Gammarus palustris in an Intertidal Salt Marsh Community

Seasonal changes in the intertidal distribution, abundance and population dynamics of the epifaunal amphipod Gammarus palustris were studied in salt marshes bordering 2 estuarine rivers flowing into the Chesapeake Bay. The amphipod populations inhabiting the Patuxent River study site showed abundance peaks during the spring and autumn, and major declines in density during the summer and winter. Populations at 2 study sites in the Rhode River showed only 1 peak of abundance during the late spring and early summer which was followed by a decline in density throughout the remainder of the year. In both rivers, the low amphipod densities observed during the winter corresponded with a subtidal migration. Migrations did not account for the low numbers observed at other times and an examination of the life cycle of this species as well as an egg—ratio analysis of the populations indicated that low densities during the summer (Patuxent) or late summer and fall (Rhode) were not due solely to life—cycle events. The tolerance of G. palustris to 3 environmental parameters was tested in the laboratory. These included low—salinity, heat/desiccation and freezing—stress experiments. Comparisons of the results with observed fluctuations of these variables at the study sites demonstrated that only freezing stress would probably cause significant mortality in intertidal populations of this species. Insufficient tolerance to this stress was postulated as the reason for the observed distributional shift to subtidal areas during the winter. Amphipod distribution within the intertidal zone at other times of the year was highly correlated with Spartina density. Substratum preference experiments indicated that this was due to a strong behavioral preference by this species for Spartina culms. Intraspecific and interspecific competition for food were tested by an analysis of 3 reproductive indices: the estimated birth rate as calculated by the egg—ratio method, the average brood size and the average brood size/ovigerous ♀. The former 2 indices declined during the early summer as a result of natural adult female mortality and a decreased proportion of ovigerous to nonovigerous ♀ ♀. The average brood size/ovigerous ♀ did not decline significantly throughout the reproductive period indicating that food limitation did not induce the observed summer decline in amphipod abundance. Intraspecific competition for space was tested in the laboratory by crowding and competitive—displacement experiments. The results indicated that competition for space was not directly responsible for the summer decrease in amphipod density but did influence amphipod distribution when Spartina culms were a limited resource. In this situation, G. palustris was capable of intraspecific displacement and evidence is presented which indicates that adults are able to displace juveniles from the preferred substratum. Interspecific competition was not examined experimentally because most of the associated fauna inhabiting the marsh beds were infaunal species. Laboratory predation experiments showed that 3 species, Fundulus heteroclitus, Rhithropanopeus harrisii and Paleomonetes pugio could potentially regulate G. palustris densities. Furthermore, F. heteroclitus predation decreased significantly with increased Spartina density and was strongly size selective for large amphipods. Rhithropanopeus harrisii and P. pugio predation was not significantly affected by Spartina density when amphipod abundance was low and predation by both species was significant with high amphipod and culm density, similar to that observed at the Rhode River sites. Although adult R. harrisii showed some indication of size selective predation, neither species was strongly size selective for large G. palustris when Spartina culms were dense. Field caging experiments combined with estimates of predator density indicated that Fundulus predation was the primary source of mortality in the Patuxent River population during the summer. The results of caging experiments in the Rhode River were inconclusive but large increases in predator density correlated with major declines in amphipod abundance. Therefore, predation is postulated as the major source of mortality during the summer and fall at the Rhode River sites. Thus, both environmental and biological factors regulate these amphipod populations with the former important during the winter only and the latter important at other times of the year.

Intraspecific competition in Tridacna crocea, a burrowing bivalve.

Intraspecific competition for space and light occurred when Tridacna crocea burrowed into coralline substratum of boulders on leeward coral reefs in the central Great Barrier Reef near Townsville, Australia. Intensity of competition was linearly related to clam density. Above about 200 clams/m2, all clams physically contacted one another and all shells sustained damage. Mortality in isolated populations due to intraspecific competition was estimated at 40%. Principles of intraspecific competition in plants were tested for applicability to T. crocea populations. Juvenile mortality due to competitive stress was density dependent. Aggregated distributions of one year old clams changed to random or regular distribution of adults. Normal size-frequency distribution for juveniles became skewed for older groups. A bimodal size-frequency distribution of the population was related to selective mortality in 1-3 year old clams. Adult mortality due to crowding was less severe but significant. Growth rates were inhibited by competition. Deformations in morphology resulted from crowding. Intraspecific competition for space and light by adults inhibited recruitment of young. Animal adaptations to reduce mortality under crowded conditions were also important. Larvae aggregated on settling and oriented with posterior ends pointed away from nearest neighbors. Positional alignment within the substratum was selectively advantageous. Burrowing posteriorly was preferential, but anterior and sideways burrowing as well as twisting within the burrow were also observed. Movement within substratum served to reduce local damage to the shell. Proteinaceous deposits secreted through perforations in the shell reduced subsequent damage. T. crocea populations exhibited many animal adaptations that reduced mortality during the first years of life, but as cohorts matured, plant-like patterns of competitive interaction became more significant.

SOCIAL ORGANIZATION WITHIN CLONES OF THE SEA ANEMONE ANTHOPLEURA ELEGANTISSIMA.

The aggregating form of the anemone Anthopleura elegantissima often lives in closely packed groups composed of genetically identical individuals. These clonal aggregations remain separated from each other because contact between non-clonemates elicits intraspecific aggression (Francis, 1973a & b). Since the anemones live in a dependable environment, are long-lived, have indeterminate growth, and reproduce sexually and asexually, and since predation does not appear to be severe, intraspecific competition for space is quite important. The ability to distinguish clonemates from non-clonemates allows the anemones to benefit from group living while interfering with all other conspecific competitors. A high proportion of the costs of this intraspecific aggression is paid by the anemones living at interclonal borders. The interclonal border warriors have more and larger acrorhagi (specialized structures used in intraspecific aggression) than clonemates elsewhere in the aggregation and were without gonads in June when many of their clonemates were ripe. They are smaller on an average than midclone anemones but not smaller than clonemates from an edge of the aggregation remote from other clones. In the field, the fission rates of warrior anemones is not higher, and may be lower than that of clonemates in other parts of the same aggregation. Lack of gonads, small size, and low fission rates probably indicate that the warriors have less energy available for growth and reproduction than do their clonemates away from the battle zone. Without physical connections among the individuals, the ability to coordinate and communicate is limited. Each anemone responds to its particular circumstances, and in so doing may fortuitously benefit its clonemates. Natural selection acts on the genotype (the clone). This is a very simple form of social organization both functionally and evolutionarily.

Polychaete Abundance Patterns in a Marine Soft‐Sediment Environment: The Importance of Biological Interactions

Samples of infauna and measurements of temperature, oxygen, salinity, and algal cover were taken from January 1969 to December 1970 at —1.2—ft tidal elevation in a mud flat dominated by polychaetes in Mitchell Bay, San Juan Island, Washington. Mortality of adults after spawning and variable larval settlement success probably explained much of the variation in population numbers of the four large and numerically important polychaete species, Lumbrineris inflata, Axiothella rubrocincta, Platynereis bicanaliculata, and Armandia brevis. No correlations were found between the abundances of numerically important species and physical factors. Exclosures constructed of 3—mm mesh plastic screening placed on the flat became covered with diatoms. Settling juveniles of tube—building species, such as P. bicanaliculata, Axiothella rubrocincta, and L. inflata, built tubes in this layer of diatoms and thus did not reach the enclosed sediment, while settling juveniles of a burrowing species, Armandia brevis, burrowed through the diatom layer and reached the sediment. Thus, cleaning the cage surfaces or removing the cage after settlement reduced abundances of tube—building species without disturbing the sediment since adults of all three numerically important tube builders experience mortality after spawning. The manipulation of tube—builder abundances showed that the burrowing species responded to space vacated by tube builders by increased settlement success. Results from experimental variation of A. brevis numbers per unit volume of sediment in the laboratory and abundance data from unmanipulated natural areas also demonstrated the presence of interspecific and intraspecific competition for space. Changes in physical factors due to algal cover had some impact on population levels but the competitive interactions and behavior patterns, revealed only by observations on the behavior of living organisms and manipulation of the infauna, demonstrated the importance of biological interactions to the determination of species abundance patterns in a soft—sediment environment.