Effects Of Species Interactions Research Articles

Notonectaexhibit threat-sensitive, predator-induced dispersal

Dispersal is a central process determining community structure in heterogeneous landscapes, and species interactions within habitats may be a major determinant of dispersal. Although the effects of species interactions on dispersal within habitats have been well studied, how species interactions affect the movement of individuals between habitats in a landscape has received less attention. We conducted two experiments to assess the extent to which predation risk affects dispersal from an aquatic habitat by a flight-capable semi-aquatic insect (Notonecta undulata). Exposure to non-lethal (caged) fish fed conspecifics increased dispersal rates in N. undulata. Moreover, dispersal rate was positively correlated with the level of risk imposed by the fish; the greater the number of notonectids consumed by the caged fish, the greater the dispersal rate from the habitat. These results suggest that risk within a habitat can affect dispersal among habitats in a landscape and thus affect community structure on a much greater scale than the direct effect of predation itself.

Experimental mixtures of dung fauna affect dung decomposition through complex effects of species interactions

Dung fauna plays an important role in dung decomposition, a key ecosystem process in nutrient cycling in grazed grasslands. The diversity of a three-species community (dung beetles, dung flies and epigeic earthworms) was systematically manipulated to produce different relative abundance distributions (evenness levels) and the resulting communities were introduced to standardised dung pats in laboratory experiments. Dung decomposition was modelled using an analysis that disentangled species identity effects and the interactions among species that contribute to the diversity effect. This revealed that the net diversity effect was composed of positive (fly–earthworm), negative (beetle–earthworm) and neutral (fly–beetle) effects of species interaction. These pairwise interactions resulted in complex, but systematically varying and predictable effects on dung decomposition as the relative abundances of species changed. Decomposition was consistently greater in communities with higher decomposer biomass. The utility of the adopted analytical approach was emphasised by comparison with an ANOVA that found that dung decomposition did not differ among evenness levels. Thus, the averaging of decomposition across different community structures within evenness levels masked the different effects of species interactions. These results highlight methodological insights into the quantification of diversity–function relationships.

Using experimental indices to quantify the strength of species interactions

Few methods for demonstrating the effects of species interactions rival that of the manipulative experiment (Kareiva and Levin 2002). The now commonly performed removal or addition of predators, competitors, or mutualists to experimentally replicated populations of recipient species has irrefutably shown that species can have important effects on each other's populations, and that the strengths of these effects can vary considerably across environmental contexts and species identities. A large body of research is directed towards understanding this variation to forecast community dynamics and dissect how species interactions regulate community structure (Chesson 2000, McCann 2000, Stachowicz 2001, Duffy 2002). It has frequently been pointed out that progress in this field will require more explicit connections between ecological theory and the realities of nature (Laska and Wootton 1998, Parker et al. 1999, Berlow et al. 2004, Agrawal et al. 2007). This requires that interaction strengths measured experimentally be appropriate to the biology of our study systems and the mathematical abstractions we ascribe to them. Here we clarify some of the assumptions made in the application of the two most commonly used indices for measuring the strengths of species interactions with manipulative removal/addition experiments: Paine's index and the dynamic index. We explain how the values these indices are intended to measure – the per capita interaction strength between two species – are typically not estimated in common currencies. We then introduce extensions to these indices that alleviate a subset of previously made assumptions and limitations. These include a reformulation of Paine's index appropriate for an open-recruitment system, and an extension of the dynamic index applicable to interactions of a particular nonlinear form. While we focus our language on predator–prey interactions, our discussions are pertinent to the measurement of species effects in other types of interactions as well (Mitchell and Wass 1996, Freckleton et al. 2009).

Hutchinson's duality: The once and future niche

The duality between "niche" and "biotope" proposed by G. Evelyn Hutchinson provides a powerful way to conceptualize and analyze biogeographical distributions in relation to spatial environmental patterns. Both Joseph Grinnell and Charles Elton had attributed niches to environments. Attributing niches, instead, to species, allowed Hutchinson's key innovation: the formal severing of physical place from environment that is expressed by the duality. In biogeography, the physical world (a spatial extension of what Hutchinson called the biotope) is conceived as a map, each point (or cell) of which is characterized by its geographical coordinates and the local values of n environmental attributes at a given time. Exactly the same n environmental attributes define the corresponding niche space, as niche axes, allowing reciprocal projections between the geographic distribution of a species, actual or potential, past or future, and its niche. In biogeographical terms, the realized niche has come to express not only the effects of species interactions (as Hutchinson intended), but also constraints of dispersal limitation and the lack of contemporary environments corresponding to parts of the fundamental niche. Hutchinson's duality has been used to classify and map environments; model potential species distributions under past, present, and future climates; study the distributions of invasive species; discover new species; and simulate increasingly more realistic worlds, leading to spatially explicit, stochastic models that encompass speciation, extinction, range expansion, and evolutionary adaptation to changing environments.

Hydraulic lift and tolerance to salinity of semiarid species: consequences for species interactions

The different abilities of plant species to use ephemeral or permanent water sources strongly affect physiological performance and species coexistence in water-limited ecosystems. In addition to withstanding drought, plants in coastal habitats often have to withstand highly saline soils, an additional ecological stress. Here we tested whether observed competitive abilities and C-water relations of two interacting shrub species from an arid coastal system were more related to differences in root architecture or salinity tolerance. We explored water sources of interacting Juniperus phoenicea Guss. and Pistacia lentiscus L. plants by conducting physiology measurements, including water relations, CO2 exchange, photochemical efficiency, sap osmolality, and water and C isotopes. We also conducted parallel soil analyses that included electrical conductivity, humidity, and water isotopes. During drought, Pistacia shrubs relied primarily on permanent salty groundwater, while isolated Juniperus plants took up the scarce and relatively fresh water stored in upper soil layers. As drought progressed further, the physiological activity of Juniperus plants nearly stopped while Pistacia plants were only slightly affected. Juniperus plants growing with Pistacia had stem-water isotopes that matched Pistacia, unlike values for isolated Juniperus plants. This result suggests that Pistacia shrubs supplied water to nearby Juniperus plants through hydraulic lift. This lifted water, however, did not appear to benefit Juniperus plants, as their physiological performance with co-occurring Pistacia plants was poor, including lower water potentials and rates of photosynthesis than isolated plants. Juniperus was more salt sensitive than Pistacia, which withstood salinity levels similar to that of groundwater. Overall, the different abilities of the two species to use salty water appear to drive the outcome of their interaction, resulting in asymmetric competition where Juniperus is negatively affected by Pistacia. Salt also seems to mediate the interaction between the two species, negating the potential positive effects of an additional water source via hydraulic lift.

Community‐level consequences of species interactions in an annual plant community

AbstractQuestion: How does the intensity of species interactions affect species and functional group composition of an annual plant community?Location: Sede Boqer, Negev Desert, Israel.Methods: The potential for competitive interactions in two annual plant communities (desert and coastal) from semi‐stabilized sand dunes was manipulated by varying seed bank density and therefore the number of potentially interacting individuals. Communities were exposed to three different irrigation regimes, mimicking precipitation at the desert site, the coastal site, and an intermediate precipitation level. Plots were maintained for 3 years, and percentage cover of each species in the plots was recorded at the end of each growing season. We used redundancy analysis to test for effects of initial density, irrigation, and year on the species and functional group composition of the communities.Results: Initial density had significant effects on species composition, and these effects remained significant over 3 years, even as total community percentage cover became more similar among treatments over time. Density effects did not depend on resource availability (irrigation level). Functional group identity or individual plant size did not predict which species would be good competitors, and a species' competitive ability did not predict its abundance in the field.Conclusions: Species interactions strongly affect community composition, and those effects carry over into subsequent years such that competition does not lead to convergence in community structure over time. However, the particular changes in composition observed were not predictable by some of the traits that have been found important in individual‐level experiments. We speculate that the outcome of competition in diverse communities will depend on multiple traits, in contrast to the outcome of individual‐level pairwise experiments. We also speculate that the shift in composition with density could mean that local variation in density may contribute to maintenance of diversity in this system.

Seasonal nitrogen dynamics of Miscanthus×giganteus and Panicum virgatum

AbstractThere is a tradeoff to consider when harvesting perennial biomass crops: harvest too late and yield declines, harvest too early and risk higher mineral contents, particularly nitrogen (N). Allowing the crop to completely senesce and recycle nutrients has several advantages, including improved feedstock quality and reduced fertilizer requirements, but it comes at a risk, particularly in temperate climates where snow and ice can reduce or destroy harvestable biomass. The effect of harvest time on the N concentration ([N]) and biomass of Panicum virgatum and Miscanthus×giganteus was evaluated at three sites in Illinois over two years. In both species [N] of standing biomass significantly declined with time (P<0.0001). Interestingly, there was no significant interaction effect of species and sample date on [N] (P=0.2888), but there was a highly significant interaction effect on the total N in standing biomass (P<0.0001). The amount of standing N was directly related to biomass yield. Seasonal changes in standing N differed among locations, suggesting that harvest time recommendations for N management depend on location. P. virgatum would have potentially removed as much as 187 kg N ha−1 if harvested green, and as little as 5 kg N ha−1 if harvested in late winter. Because of higher biomass yields, M. ×giganteus standing N ranged from 379 kg N ha−1 in June to <17 kg N ha−1 in February. Importantly, there was little overall change in [N] between an early winter (December) harvest and a late winter (February/March) harvest, indicating the benefits of N cycling in the system can be realized by end of the growing season and thus, at least from an N economy perspective, there is no reason to risk yield losses by delaying harvest over the winter.

Analyzing the tradeoffs among ecological and fishing effects on an example fish community: A multispecies (fisheries) production model

Species interactions such as predation or competition can have notable implications for fish population dynamics. Stock status and associated biological reference points can be misrepresented if these interactions are not considered. Here we present a multispecies, biomass production model (MS-PROD) developed by incorporating modifications to the Schaefer production model. The modifications explicitly emphasize a functional group approach, highlighting the effects of species interactions that include competition between species within a group, competition between groups, and predation. The mathematical formulation also includes constraints on carrying capacity for both the entire system and for individual groups. We applied the model as initialized to the Northeast U.S. Large Marine Ecosystem finfish community. We then executed simulations designed to explore the behavior of the model with respect to fishery exploitation and ecological interactions. Collectively, the results demonstrated the utility, and the need, for incorporating ecological effects into fisheries models.

The Effects of Species Interaction and Pond Stocking Density on Tilapia Aquaculture:

This paper describes the effects of predatory catfishes Clarias gariepinus (Burchell) and Heterobranchus bidorsalis (Geoffrey Saint-Hilaire) and pond stocking density on the culture of tilapia species which display different parental care strategies. In the presence of catfishes, the maternal mouth-brooder O. niloticus (Linnaeus), and the bi-parental mouth-brooder S. galiliaeus (Steindachner) reproduced easily. However, the substrate-brooder T. guineensis (Bleeker) bred with difficulty as the persistent, aggressive, bottom feeding habit of the catfishes inhibited reproduction to some extent by destroying spawning nests and killing developing eggs, or by frightening the breeders to abandon ventilation and parental care of developing eggs inside the nests. Therefore the control of tilapia overpopulation with predatory catfishes to enhance tilapia growth is more likely to be successful in substrate-brooders than in mouth-brooders. T. guineensis was also more susceptible to direct catfish predation than either O. niloticus or S. galilaeus probably because of its more attractive body colouration. When the three tilapia species were reared together, T. guineensis built spawning nests almost exclusively in the shallow littoral zone, whereas O. niloticus and S. galilaeus concentrated their nests in the deeper part of the pond. Site-dependent segregation of the tilapia species at the time of breeding could be a strategy to avert inter-specific territorial competition. Offspring population of O. niloticus showed an inverse relationship with pond stocking density. As stocking density was increased, agonistic encounters between territorial males intensified and inhibited successful fertilization and recruitment. Growth rate of O. niloticus decreased with pond stocking density up to 3 fish/m2, but the differences were not significant. Journal of the Ghana Science Association Vol. 10 (2) 2008: pp. 12-19

Nitrogen and Phosphorus Release from Mixed Litter Layers is Lower than Predicted from Single Species Decay

Ecosystem-level nutrient dynamics during decomposition are often estimated from litter monocultures. If species effects are additive, we can statistically predict nutrient dynamics in multi-species systems from monoculture work, and potential consequences of species loss. However, if species effects are dependent on interactions with other litter species (that is, non-additive), predictions based on monoculture data will likely be inaccurate. We conducted a 3-year, full-factorial, mixed-litter decomposition study of four dominant tree species in a temperate forest and measured nitrogen and phosphorus dynamics to explore whether nutrient dynamics in mixtures were additive or non-additive. Following common approaches, we used litterfall data to predict nutrient dynamics at the ecosystem-level. In mixtures, we observed non-additive effects of litter mixing on nutrient dynamics: the presence of nutrient-rich species in mixture facilitated nutrient release, whereas nutrient-poor species facilitated nutrient retention. Fewer nutrients were released from mixtures containing high-quality litter, and more immobilized from mixtures containing low-quality litter, than predicted from monocultures, creating a difference in overall nutrient release between predicted and actual dynamics in litter mixtures. Nutrient release at the ecosystem-level was greatly overestimated when based on monocultures because the effect of species interactions on nutrient immobilization was not accounted for. Our data illustrate that the identity of species in mixtures is key to their role in non-additive interactions, with repercussions for mineral nutrient availability and storage. These results suggest that predictions of ecosystem-level nutrient dynamics using litter monoculture data likely do not accurately represent actual dynamics because the effects of litter species interactions are not incorporated.

Interactions between hydrology, burning and contrasting plant groups during the millennial‐scale development of sub‐montane wet heath

AbstractQuestion:How might contrasting plant groups interact to confer ecosystem stability during the development of a wet heath: i.e. in response to two major environmental drivers, past hydrologic change and burning?Location:Rannoch Moor, Scotland.Methods:Three peat cores were used to reconstruct vegetation change, surface moisture and burning phases, during wet heath development for a radiocarbon‐dated period from ca. 9500–1000 yr BP.Results:Statistical analysis of peat cores revealed significant relationships between burning phases and past periods of inferred surface dryness. Vegetation elements were related in the palaeoecological record to surface dryness (Ericaceae), wetness (Sphagnum, monocotyledons, and Racomitrium) and periods of burning (i.e. negative correlation of Racomitrium and monocotyledon remains with charcoal). However, correlations between plant groups could not be adequately explained by their equivalent direct response to hydrology and burning, and the effects of species interactions are invoked.Conclusions:The results indicate millennial‐scale stability of the wet heath ecosystem in response to past environmental change (i.e. hydrology and burning). This stability is conferred by interaction between a diversity of plant groups, enabling local shifts in vegetation composition in response to environmental drivers. This long‐term stability of the mire ecosystem forms a template against which present‐day threats (e.g. pollution, climate change) should be critically assessed.

Species Associations in a Heterogeneous Sri Lankan Dipterocarp Forest

We used point pattern analysis to examine the spatial distribution of 46 common tree species (diameter at breast height >10 cm) in a fully mapped 500x500-m tropical forest plot in Sinharaja, Sri Lanka. We aimed to disentangle the effect of species interactions (second-order effects) and environment (first-order effects) on the species' spatial distributions. To characterize first-order associations (segregation, overlap), we developed a classification scheme based on Ripley's K and nearest-neighbor statistics. We subsequently used heterogeneous Poisson null models, accounting for possible environmental heterogeneity, to reveal significant uni- and bivariate second-order interactions (regularity, aggregation and repulsion, attraction). First-order effects were strong; overall, 53% of all species pairs occupied largely disjoint areas (segregation), 40% showed partial overlap, and 6% overlapped. Only 5% of all species pairs showed significant second-order effects, but about half of the species showed significant intraspecific effects. Significant plant-plant interactions occurred mostly within 2-4 m and disappeared within 15-20 m of the focal plant. While lack of significant species interactions suggests support for the unified neutral theory, species' observed spatial segregation does not support the assumptions of the neutral theory. The strong observed tendency of species to segregate may have supplementary effects on other processes promoting species coexistence.

Including species interactions in risk assessments for global change

AbstractMost ecological risk assessments for global change are restricted to the effects of trends in climate or atmospheric carbon dioxide. In order to move beyond investigation of the effects of climate alone, the climex™ model was extended to investigate the effects of species interactions, in the same or different trophic levels, along environmental gradients on a geographical scale. Specific needs that were revealed during the investigations include: better treatment of the effects of temporal and spatial climatic variation; elucidation of the nature of boundaries of species ranges; data to quantify the role of species traits in interspecies interactions; integrated observational, experimental, and modelling studies on mechanisms of species interactions along environmental gradients; and high‐resolution global environmental datasets. Greater acknowledgement of the shared limitations of simplified models and experimental studies is also needed. Above all, use of the scientific method to understand representative species ranges is essential. This requires the use of mechanistic approaches capable of progressive enhancement.

PREDICTING EXTINCTION RISK IN SPITE OF PREDATOR–PREY OSCILLATIONS

Most population viability analyses (PVA) assume that the effects of species interactions are subsumed by population-level parameters. We examine how robust five commonly used PVA models are to violations of this assumption. We develop a stochastic, stage-structured predator-prey model and simulate prey population vital rates and abundance. We then use simulated data to parameterize and estimate risk for three demographic models (static projection matrix, stochastic projection matrix, stochastic vital rate matrix) and two time series models (diffusion approximation [DA], corrupted diffusion approximation [CDA]). Model bias is measured as the absolute deviation between estimated and observed quasi-extinction risk. Our results highlight three generalities about the application of single-species models to multi-species conservation problems. First, our collective model results suggest that most single-species PVA models overestimate extinction risk when species interactions cause periodic variation in abundance. Second, the DA model produces the most (conservatively) biased risk forecasts. Finally, the CDA model is the most robust PVA to population cycles caused by species interactions. CDA models produce virtually unbiased and relatively precise risk estimates even when populations cycle strongly. High performance of simple time series models like the CDA owes to their ability to effectively partition stochastic and deterministic sources of variation in population abundance.

Comparison of growth, nutrition and soil properties of pure and mixed stands of Populus deltoides and Alnus subcordata

Concerns about decline in soil fertility and long-term productivity of fast-growing plantations have promoted interest in using nitrogen-fixing trees in mixed species plantations. Populus deltoides and Alnus subcordata were planted in five proportions (100P, 67P:33A, 50P:50A, 33P:67A, 100A) in Noor, Iran. After 7 years, the effects of species interactions on tree growth and nutrient concentration in live and senescent leaves and soil properties were assessed. Diameter at breast height and total height of individual Populus trees were positively affected by the presence of Alnus. Nitrogen concentrations in fully expanded and senescent leaves of Populus were higher in mixed plantations than monoculture plantations. The results of nutrition and nutrient return and growth indicated that mixed plantations of these two species were more productive and sustainable than their monoculture plantations. Within the framework of this experiment, it appeared that production was maximized when these two species were grown together in the relative proportions of 50% Populus and 50% Alnus.

Effect of species interactions on landscape abundance patterns

SummaryWe develop a process‐based bioenergetic model that incorporates population dynamics to predict the abundance trends for Anolis lizards along elevation gradients in the Lesser Antilles islands. Model outcomes are compared with empirical abundance trends on islands with and without species interactions and with differential topography.The bioenergetic model incorporating body size, thermal physiology and prey abundance qualitatively predicts how lizard abundance declines with elevation for solitary anole species. Empirical elevation trends on northern and southern one‐species islands have similar slopes but different intercepts at sea level. The greater anole abundance on the southern islands is predicted by the model when parameterized with the empirically observed higher insect abundance.Anole abundance patterns on two‐species islands diverge from the bioenergetic model predictions. One species is more abundant at sea level and the other more abundant at higher elevations compared with the trend for solitary anoles. Species interactions modify population responses to elevation gradients.

Climate change effects on species interactions in an alpine plant community

Summary I examined the role of species interactions on the population dynamics of the herb Thalictrum alpinum and the sedge Carex vaginata by removing the dwarf shrub Dryas octopetala over four growing seasons at Finse, in the alpine region of south Norway, Furthermore, by increasing temperature (open top chambers) and nutrient availability (nutrient addition), I assessed the effects of climate warming on biotic interactions. Dryas removal increased the number of Thalictrum and Carex leaves, and flowering frequency of Carex. Flower stems and leaf stalks of Thalictrum, and the leaves of Carex, became significantly shorter following Dryas removal. Warming and nutrient addition increased vegetative plant growth, whereas warming alone had positive effects on sexual reproductive effort of the target species. My results suggest that there is both competition for nutrients, and a facilitative shelter effect of Dryas on its neighbours. Species interactions affected population dynamics of Thalictrum and Carex. Interactions between the impacts of Dryas removal and abiotic factors on leaf production, suggested that interactions between Dryas and neighbouring species might be modified if temperature and, in particular, nutrient availability increase under global warming. This study shows that both biotic interactions and abiotic environmental conditions may affect alpine plant population dynamics. Furthermore, it shows that climate change may modify species interactions. Species interaction effects should be included in climate change experiments and in future models predicting plant community changes under global warming.

The importance of habitat heterogeneity, biotic interactions and dispersal in abundance–occupancy relationships

Summary In simple microcosm systems, the form of interspecific abundance–occupancy relationships has been found to be dependent on biotic interactions. However, in more complex systems such effects may be obscured by those of habitat heterogeneity. Here we test this proposal using laboratory microcosms of protists and bacteria. The independent effects of species interactions and heterogeneity were tested by comparison of the abundance–occupancy relationship formed in multiple habitat patch systems containing all species together, with that relationship formed by combining data from equivalent systems containing each protist species alone and between homogeneous and heterogeneous environments. There was more residual variation about positive interspecific abundance–occupancy relationships formed in heterogeneous environments in interacting and non‐interacting communities as the majority of species were more restricted in the number of patches they could occupy compared to homogeneous landscapes. Abundance–occupancy relationships in interacting communities were better defined than those in non‐interacting communities. The inclusion of interspecific interactions caused a reduction in the abundance and occupancy of the majority of species and changed the position of species within the relationship. Our results show that biotic interactions influence the abundance–occupancy relationships even with imposed environmental heterogeneity. However, in heterogeneous environments, for some species these processes occurred in fewer patches, causing increased residual variation about positive interspecific abundance–occupancy relationships compared to homogeneous environments.

Improved fallows: effects of species interaction on growth and productivity in monoculture and mixed stands

To derive optimal benefits from short-term planted legume fallows, farmers need to make important initial decisions on the establishment and growth performance of specific species in monoculture stands and in mixtures. We hypothesized that species with contrasting growth characteristics could be mixed to optimize aboveground resource capture due to their complementary or compensatory gains in resource acquisition. A selection of tree/shrub/herbaceous legumes planted in monoculture and mixed stands were evaluated for growth, biomass and nitrogen productivity on a Kandiudalfic Eutrudox in western Kenya. Species evaluated included: sesbania ( Sesbania sesban (L.) Merr.), crotalaria ( Crotalaria grahamiana Wight and Arn.), pigeonpea ( Cajanus cajan (L.) Millsp.), and siratro ( Macroptilium atropurpureum (DC.) Urb). Total aboveground biomass ranged from 5 to 12 Mg ha −1 (monocultures) and 3.4–8 Mg ha −1 (mixtures). N yield per plant was linearly correlated with total plant biomass ( R 2=0.95,slope=0.018) across all of the fallows, despite different amounts of leaf and wood with widely differing N concentrations being present with the different species. Biomass and N yield of sesbania was negatively affected by mixing with other species. For instance, sesbania N yield decreased when mixed with pigeonpea (54%) or crotalaria (67%). Crotalaria and pigeonpea established best under relay cropping with maize and emerged to be better competitors in mixtures than sesbania and siratro. Results of this study suggest that mixing species in fallows provide a better risk management strategy through compensatory biomass and nutrient production gains obtained from the strongly competing species.

Fluctuation in stock properties of north‐east Arctic cod related to long‐term environmental changes

AbstractFrom a historic perspective, the north‐east Arctic cod stock, which is found in the Barents Sea–Svalbard region, has been the most productive gadoid stock in the Atlantic. Variation in catch has always been large, but during the last 10–15 years catch and stock abundance have reached the lowest level on record. Three major causes of variation have been discussed: (i) stock reduction through exploitation; (ii) environmental influences on recruitment; and (iii) species interaction effects on maturation, growth and mortality. In addition, interactions among these three sources might be important. The influence of each specific factor is difficult to evaluate from incidental observations and short‐term time series. In this respect, the time series on catches and on biological and environmental information of this stock, which partly extend back to the 19th century, occupy a unique position in comparison to data on most other stocks. In this paper, fluctuations in catch and stock abundance are compared with changes in recruitment, size/age and growth. This information is discussed in view of historic variation in ecology and environment. The stock has been under particularly high exploitation pressure since the mid‐1970s. Further, large changes in growth rates and poor recruitment to the commercially exploited stock are characteristic of late 1980s and throughout the 1990s. The analysis shows that substantial long‐term variation might underlie short‐term variability, and more importantly, that long‐term changes roughly coincide with similar fluctuations in the environment. Such factors might substantially affect the relationship between spawning stock and recruitment, which is also apparent from the difference in conclusions reached by various published studies. Consequently, it is suggested that using a steady‐state perspective for the population dynamics may lead to mismanagement and to a reduction of the long‐term yield from this stock.