Testosterone,cortisol, and human competition

Testosterone and cortisol figure prominently in the research literature having to do with human competition. In this review, we track the history of this literature, concentrating particularly on major theoretical and empirical contributions, and provide commentary on what we see as important unresolved issues. In men and women, athletic competition is typically associated with an increase in testosterone (T) and cortisol (C). Hormone changes in response to non-athletic competition are less predictable. Person (e.g., power motivation, mood, aggressiveness, social anxiety, sex, and baseline levels of T and C) and context (e.g., whether a competition is won or lost, the closeness of the competition, whether the outcome is perceived as being influenced by ability vs. chance, provocations) factors can influence hormone responses to competition. From early on, studies pointed to a positive relationship between T and dominance motivation/status striving. Recent research, however, suggests that this relationship only holds for individuals with low levels of C – this is the core idea of the dual-hormone hypothesis, and it is certain that the broadest applications of the hypothesis have not yet been realized. Individuals differ with respect to the extent to which they embrace competition, but the hormonal correlates of competitiveness remain largely unexplored. Although rapid increases in both T and C associated with competition are likely adaptive, we still know very little about the psychological benefits of these hormonal changes. Administration studies have and will continue to contribute to this inquiry. We close with a discussion of what, we think, are important methodological and mechanistic issues for future research.     

Women's intercollegiate athletic competition: Cortisol,testosterone, and the dual-hormone hypothesis as it relates to status among teammates

Recent research suggests that testosterone and cortisol jointly regulate dominance motivation and, perhaps, the status relationships that are affected by it. For this article, the results of six different studies of women's intercollegiate athletic competition were combined to give a sample size of almost ninety women for whom we had before- and after-competition values for salivary cortisol and testosterone for at least one and sometimes two competitions. For many of these women, we had surveys that allowed us to assess their status with teammates. In no matter what sport (soccer, softball, volleyball, and tennis) levels of salivary cortisol and testosterone increased when women participated in athletic competition. Salivary levels of C and T appear to rise in parallel during competition and increases in levels of one hormone are significantly related to increases in the other. Salivary levels of these hormones typically decreased for teammates who did not play but watched the competition from the sidelines. For women who played in two competitions, individual differences in the positive effect of competition on cortisol and testosterone were conserved from one competition to the next, affirming the personal consistency of endocrine responses to competition. Status with teammates was positively related to before-competition levels of testosterone, but only for women with relatively low before-competition levels of cortisol. This result provides novel support for the “dual-hormone hypothesis” as it relates to predicting social status in women's athletic teams — natural social groups of individuals who know each other and whose social hierarchy has evolved over the course of practice and play for at least one and, in some cases, several years of intercollegiate athletic competition.     

How conception risk affects competition and cooperation with attractive women and men

We investigated competition and cooperation for resources across the menstrual cycle in the context of bargaining games. Although bargaining has been studied within an evolutionary framework, little attention has been paid specifically to the role of mating motives in economic behavior. To investigate how motives related to reproductive success affect bargaining, participants at high or low risk for conception or who were on oral contraceptives played ultimatum and dictator games with partners who varied in sex and facial attractiveness. In ultimatum games, women in the fertile phase were more competitive over resources with attractive women than with less attractive women. Intrasexual competition was not observed in dictator games. Women were more cooperative with attractive men than with less attractive men in both games, regardless of fertility status. Low fertility women were more cooperative with attractive members than with less attractive members of both sexes in both games. Results support the view that, during periods of high fertility, when women are most intrasexually competitive for mates, withholding resources from potential rivals would enable women to gain the means to enhance their attractiveness and weaken competitors' abilities to do the same at a time when relative advantages in appearance are most crucial to reproductive success. The lack of a fertility effect for cooperation with potential mates supports the view that displays of generosity accrue benefits for women across the cycle in their efforts to attract men who will invest in relationships.     

The effects of competition and implicit power motive on men's testosterone,emotion recognition,and aggression

A contribution to a special issue on Hormones and Human Competition.We investigated the effects of competition on men's testosterone levels and assessed whether androgen reactivity was associated with subsequent emotion recognition and reactive and proactive aggression. We also explored whether personalized power (p Power) moderated these relationships. In Study 1, 84 males competed on a number tracing task and interpreted emotions from facial expressions. In Study 2, 72 males competed on the same task and were assessed on proactive and reactive aggression. In both studies, contrary to the biosocial model of status (Mazur, 1985), winners' testosterone levels decreased significantly while losers' levels increased, albeit not significantly. Personalized power moderated the effect of competition outcome on testosterone change in both studies. Using the aggregate sample, we found that the effect of decreased testosterone levels among winners (compared to losers) was significant for individuals low in p Power but not for those with medium or high p Power. Testosterone change was positively related to emotion recognition, but unrelated to either aggression subtype. The testosterone-mediated relationship between winning and losing and emotion recognition was moderated by p Power. In addition, p Power moderated the direct (i.e., non-testosterone mediated) path between competition outcome and emotion recognition and both types of aggression: high p-Power winners were more accurate at deciphering others' emotions than high p-Power losers. Finally, among high p-Power men, winners aggressed more proactively than losers, whereas losers aggressed more reactively than winners. Collectively, these studies highlight the importance of implicit power motivation in modulating hormonal, cognitive, and behavioral outcomes arising from human competition.     

Intra-sexual competition alters the relationship between testosterone and ornament expression in a wild territorial bird

In a reliable signalling system, individual quality is expected to mediate the costs associated with ornamental displays, with relatively lower costs being paid by individuals of higher quality. These relative costs should depend not only on individual quality, but also on levels of intra-sexual competition. We explored the current and delayed effects that testosterone implants have on bird ornamentation in populations with contrasted population densities, as a proxy for intra-sexual competition. In a replicated experiment, we manipulated testosterone in 196 yearling male red grouse Lagopus lagopus scoticus in autumn in populations of high and low levels of intra-sexual competition. Males were assigned to one of three exogenous testosterone (T) treatments: empty implants (T0), small T implants (T1) or larger T implants (T2). We monitored subsequent changes in testosterone levels, ornament size and carotenoid-based colouration, carotenoid levels and body condition from autumn to spring. Testosterone implants increased testosterone levels, comb redness and comb size, and decreased body condition but these effects depended on levels of intra-sexual competition. Specifically, T2-implanted birds increased testosterone levels and comb size more, and reduced body condition more, in populations where intra-sexual competition was low. In the following spring, testosterone levels of T2-treated birds kept increasing in populations where intra-sexual competition was high but not in populations where intra-sexual competition was low. Our results highlight that levels of intra-sexual competition alter the relationship between testosterone levels and ornament expression, influencing their condition-dependence; they also indicate that the outcome of standard hormone manipulation conducted in free-living animals vary depending on the population context.     

Hormonal response to competition among male coalitions

Previous research has shown that testosterone (T) and cortisol (C) are released in response to a wide variety of social stimuli including dyadic (one on one) competitive events, but humans also compete as groups. Here we report results from a pilot study of hormonal responses to competition between male coalitions. Salivary T and C levels were assessed in adult males from a rural Caribbean village who competed at dominoes, as two-man teams, against (a) familiar men from their own village (within coalition), and (b) strangers from another village (between coalitions). Analyses indicate that both T and C levels were higher and responses more pronounced for between-village competition than for within-village competition, but we could not compare responses to victory and defeat in the between-village case, since our subjects happened to win both such contests. Further studies of endocrine responses in the context of coalitional competition are warranted.     

A 7-week follow-up study of the behaviour of testosterone and cortisol during the competition period in rowers

Nine rowers (six men of the regional and three women of the national top class) participated in the study. During 7 consecutive weeks of the competition period serum testosterone (T), SHBG, cortisol (C) and urea were determined at the same time every morning under fasting conditions. From the concentrations of T and SHBG the free testosterone fraction (T/SHBG) was calculated, and from the concentrations of T and C the ratio of T/C was derived. The object of the investigation was to gather information on a potentially altered anabolic-catabolic hormone relationship dependent upon the intensity of the individual training periods. All rowers showed a continuous decrease in T, T/SHBG and T/C during the observation period. A week of regenerative training halted the decrease. In two of the oarsmen who discontinued their training after 2 and 3 weeks respectively, T, T/SHBG and T/C showed a normalization in the following weeks. In all subjects the concentrations of urea increased during the first 2 weeks and decreased during the subsequent weeks of intense training and competition. The findings suggest an increase in catabolic activity in periods of intensive physical strain, including competitions. Regenerative phases of training seem to reduce the anabolic-catabolic imbalance.     

Competition-related testosterone,cortisol, and perceived personal success in recreational women athletes

Thirty-five women participating in one or more intramural flag-football games provided saliva samples before, immediately after, and 10 min after competition and completed an after-competition questionnaire appraising their own performance during the game. As seen in other studies of elite athletes, these recreational athletes, on average, showed significant elevations in testosterone (T) and cortisol (C) across the competition period – the “competition effect”. In winners and losers, T levels at all time points measured were positively related to athletes' appraisals of their own individual performance. Results from this study show that the competition effect for T and C is evident in recreational women athletes and provide preliminary evidence about the relationship between cognitive appraisal and competition-related T levels.     

Variation in fecal testosterone levels, inter-male aggression, dominance rank and age during mating and post-mating periods in wild adult male ring-tailed lemurs (Lemur catta)

In primate species exhibiting seasonal reproduction, patterns of testosterone excretion in adult males are variable: in some species, peaks correlate with female receptivity periods and heightened male-male aggression over access to estrous females, in others, neither heightened aggression nor marked elevations in testosterone have been noted. In this study, we examined mean fecal testosterone ( f T) levels and intermale aggression in wild adult male ring-tailed lemurs residing in three groups at Beza Mahafaly Reserve, Madagascar. Results obtained from mating and post-mating season 2003 were compared to test Wingfield et al. [1990. Am Nat 136:829-846] "challenge hypothesis", which predicts a strong positive relationship between male testosterone levels and male-male competition for access to receptive females during breeding season. f T levels and rates of intermale aggression were significantly higher during mating season compared to the post-mating period. Mean f T levels and aggression rates were also higher in the first half of the mating season compared with the second half. Number of males in a group affected rates of intermale agonism, but not mean f T levels. The highest-ranking males in two of the groups exhibited higher mean f T levels than did lower-ranking males, and young males exhibited lower f T levels compared to prime-aged and old males. In the post-mating period, mean male f T levels did not differ between groups, nor were there rank or age effects. Thus, although male testosterone levels rose in relation to mating and heightened male-male aggression, f T levels fell to baseline breeding levels shortly after the early mating period, and to baseline non-breeding levels immediately after mating season had ended, offsetting the high cost of maintaining both high testosterone and high levels of male-male aggression in the early breeding period.     

Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the 'challenge hypothesis'

The challenge hypothesis posits that acute increases in testosterone (T) during male-male competition enhance performance and survivability while limiting the physiological costs of consistently high T. Human challenge hypothesis research focuses on young men in industrial populations, who have higher baseline T levels than men in subsistence populations. We tested whether the Tsimane, pathogenically stressed forager-horticulturalists of the Bolivian Amazon, would express acute T increases in response to physical competition. Saliva was collected from 88 Tsimane men (aged 16-59 years) before and after a competitive soccer match. Tsimane men had significantly lower baseline levels of T (β = -0.41, p < 0.001) when compared with age-matched United States (US) males. Linear mixed-effects models were used to establish that T increased significantly immediately following competition (β = 0.23, p < 0.001), remaining high 1 h later (β = 0.09, p = 0.007); equivalent to 30.1 and 15.5 per cent increases in T, respectively. We did not find larger increases in T among winners (p = 0.412), although T increases were positively associated with self-rated performance (β = 9.07, p = 0.004). These results suggest that despite lower levels of T than US males, Tsimane males exhibit acute increases in T at the same relative magnitude reported by studies in industrialized settings, with larger increases in T for those who report better individual performance.     

Effects of nutrient and soil moisture on competition between shape Carex stricta,shape Phalaris arundinacea,and shape Typha latifolia

We investigated the importance of nutrients, soil moisture, arbuscular mycorrhizal fungi (AMF), and interspecific competition levels on the biomass allocation patterns of three wetland perennial plant species, Carex stricta Lam., Phalaris arundinacea L., and Typha latifolia L. A factorial experiment was conducted with high-low nutrient levels, high-low soil moisture levels, and with and without AMF inoculation. Under the experimental conditions, plant inoculation by AMF was too low to create a treatment and the AMF treatment was dropped from the total analysis. P. arundinacea and T. latifolia biomass were 73% and 77% higher, respectively, in the high nutrient treatment compared to the low nutrient treatment. Biomass allocation between shoots and roots remained relatively constant between environmental treatments, although shoot:root ratios of P. arundinacea declined in the low nutrient treatment. For C. stricta, the high nutrient and soil moisture treatments resulted in an increase in biomass of 50% and 15%, respectively. Shoot:root ratios were nearly constant among all environmental conditions. Biomass of T. latifolia and C. stricta was greatly decreased when grown with P. arundinacea. The rapid, initial height growth of P. arundinacea produced a spreading, horizontal canopy that overshadowed the vertical leaves of T. latifolia and C. stricta throughout the study. This pattern was repeated in both high and low nutrient and soil moisture treatments. When grown with P. arundinacea, C. stricta and T. latifolia significantly increased their mean shoot height, regardless of the nutrient or soil moisture level. The results of this experiment suggest that C. stricta and T. latifolia were light limited when growing with P. arundinacea and that canopy architecture is more important for biomass allocation than the other environmental conditions tested. The results also suggest that Phalaris arundinacea is an inherently better competitor (sensu Grime 1979) than C. stricta or T. latifolia.     

Efficiency,intrinsic competition and interspecific host discrimination of Copidosoma desantisi and Trichogramma evanescens,two parasitoids of Phthorimaea operculella

Trichogramma evanescens West. (Hymenoptera: Trichogrammatidae) and Copidosoma desantisi Annecke & Mynhardt (Hymenoptera: Encyrtidae) are potential parasitoids of the potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in Egypt. Discrimination of a parasitized host from an unparasitized host would prevent wasting of time, eggs and reduce competition with conspecifics or heterospecifics. Therefore, we evaluated interspecific host discrimination, multiparasitism and intrinsic competition between the two wasp species. In a choice test, females of T. evanescens showed high interspecific host discrimination only when they were offered 2-day-old C. desantisi parasitized and unparasitized PTM eggs. In contrast, C. desantisi showed high host discrimination and preferred unparasitized eggs to PTM eggs harboring 2-h- or 2-day-old T. evanescens’ eggs. We also evaluated the effect of different introduction sequences on the efficacy of the two wasps. Dissection data indicated that the two parasitoids had a negative impact on each other. There was a significant reduction in the total number of deposited eggs as well as total number of parasitized hosts by each parasitoid. Regarding the rearing experiment, the total number of T. evanescens-induced black eggs or C. desantisi formed mummies in combined treatments was significantly lower than in single parasitoid treatments (control). Moreover, C. desantisi was inferior and did not develop from any multiparasitized host regardless of oviposition order. It was suggested that combined release of the two wasps would not elevate rate of parasitism over that of single parasitoid treatments and competition between them would reduce their efficacy.     

Antigenic competition and genetic control of the immune response. A hypothesis for intramolecular competition

A study has been made of antigenic competition between the (Phe,Glu) and Pro-Lys regions of three synthetic multichain polypeptides, (Phe,Glu)-Ala-Lys, (Tyr,Glu)-Pro-Lys and (Phe,Glu)-Pro-Lys. Two strains of mice have been compared, C3H/HeJ, potentially high responders to both (Phe,Glu) and Pro-Lys, and DBA/1, high responders to (Phe,Glu), but genetic low responders to Pro-Lys. In C3H/HeJ, both intramolecular competition, within the (Phe,Glu)-Pro-Lys molecule, and intermolecular competition, with mixtures of (Tyr,Glu)-Pro-Lys and (Phe,Glu)-Ala-Lys occur. In general, Pro-Lys is the dominant determinant and suppresses the response to (Phe, Glu). In DBA/1, on the other hand, intramolecular competition is absent, but intermolecular competition is still present. The injection of the polyribonucleotide poly (A)·poly (U) corrects the low response to Pro-Lys in DBA/1, and at the same time restores intramolecular competition. Intramolecular competition is, therefore, related to the level of the antibody response to the dominant antigenic region, Pro-Lys. In contrast, intermolecular competition is independent of the antibody response to Pro-Lys, but is related to the ratio of the antigens (Tyr,Glu)-Pro-Lys and (Phe,Glu)-Ala-Lys in the mixture injected.A model is suggested in which intramolecular competition is a result of competition between specific B cells for limiting antigen. The model relates competition to original antigenic sin and the enhancement and suppression mediated by antibody. Intermolecular competition seems to have a different mechanism and to be a T cell effect. The relevance of these findings to studies on the genetic control of the immune response is discussed.     

Group‐level competition influences urinary steroid hormones among wild red–tailed monkeys,indicating energetic costs

Various theories emphasize that intergroup competition should affect intragroup cooperation and social relationships, especially if the cost of intergroup competition outweighs that of intragroup competition. This cost of intergroup competition may be quantified by changes in physiological status, such as in the steroid hormones cortisol (C) and testosterone (T), which rise or are depressed during periods of energetic stress, respectively. Here we tested for changes in urinary C and T after intergroup encounters (IGEs) among wild red‐tailed monkeys (Cercopithecus ascanius), a species that experiences frequent intergroup feeding competition, at the Ngogo station in Kibale National Park, Uganda. We assayed 108 urine samples, of which 36 were collected after IGEs, from 23 individuals in four social groups. Bayesian multilevel models controlling for various confounds revealed that IGEs increased C and decreased T relative to baseline, consistent with an energetic cost to IGEs. The C change was more apparent in samples collected early after IGEs, suggesting an anticipatory increase, whereas the T change was stronger in later samples, suggesting sustained energetic trade‐offs. Hormone responses were not affected by the IGE outcome. This cost to intergroup competition, together with little evidence for intragroup competition in redtails and other guenons, establishes an interesting test case for theories emphasizing the effect of intergroup competition on intragroup cooperation.     

Prepregnancy cardiovascular risk factors as predictors of pre-eclampsia: population based cohort study

Objective To examine the effect of cardiovascular risk factors before pregnancy on risk of pre-eclampsia.Design Population based prospective study.Setting Linkage between a Norwegian population based study (Nord-Trøndelag health study, HUNT-2) and Norway''s medical birth registry.Participants 3494 women who gave birth after participating in the Nord-Trøndelag health study at baseline; of whom 133 (3.8%) delivered after a pre-eclamptic pregnancy.Main outcome measure Odds ratio of developing pre-eclampsia.Results After adjustment for smoking; previous pre-eclampsia; parity; maternal age, education, and socioeconomic position; and duration between baseline measurements and delivery, positive associations were found between prepregnancy serum levels of triglycerides, cholesterol, low density lipoprotein cholesterol, non-high density lipoprotein cholesterol, and blood pressure and risk of pre-eclampsia. The odds ratio of developing pre-eclampsia for women with baseline systolic blood pressures greater than 130 mm Hg (highest fifth) was 7.3 (95% confidence interval 3.1 to 17.2) compared with women with systolic blood pressures less than 111 mm Hg (lowest fifth). Similar results were found for nulliparous and parous women. Women who used oral contraceptives at baseline had half the risk of pre-eclampsia compared with never or former users (0.5, 0.3 to 0.9).Conclusion Women with cardiovascular risk factors may be predisposed to pre-eclampsia.     

Testosterone, cortisol, and mood in a sports team competition

In humans, hormonal responses to winning/losing and their relationships to mood and status change have mostly been examined in individual athletic competitions. In this study, the salivary testosterone (T) and cortisol (C) and mood responses to a real match between two professional basketball teams were investigated. Data about individuals' contributions to outcome, performance appraisal, and attribution of outcome to internal/external factors were also collected. Results did not show statistically significant different T and C responses depending on the outcome. Negative mood was significantly enhanced, especially in the losers, while winners showed a better appraisal of team performance and a more internal attribution. T response did not show a significant relationship with mood changes, but it correlated positively with the "score/time playing" ratio, an indicator of individual participation in the outcome. Furthermore, T response correlated negatively with external attribution in winners and positively in losers. These results indicate that in a real, highly competitive situation, T changes are not directly a response to the outcome, but rather to the contribution the individual makes to it and to the causes he attributes.     

Causal attribution and psychobiological response to competition in young men

A contribution to a special issue on Hormones and Human Competition.Psychoneuroendocrine effects of competition have been widely accepted as a clear example of the relationship between androgens and aggressive/dominant behavior in humans. However, results about the effects of competitive outcomes are quite heterogeneous, suggesting that personal and contextual factors play a moderating role in this relationship. To further explore these dimensions, we aimed to examine (i) the effect of competition and its outcome on the psychobiological response to a laboratory competition in young men, and (ii) the moderating role of some cognitive dimensions such as causal attributions. To do so, we compared the responses of 56 healthy young men faced with two competitive tasks with different instructions. Twenty-eight men carried out a task whose instructions led subjects to think the outcome was due to their personal performance (“merit” task), whereas 28 other men faced a task whose outcome was attributable to luck (“chance” task). In both cases, outcome was manipulated by the experimenter. Salivary steroid hormones (testosterone and cortisol), cardiovascular variables (heart rate and blood pressure), and emotional state (mood and anxiety) were measured at different moments before, during and after both tasks. Our results did not support the “winner-loser effect” because no significant differences were found in the responses of winners and losers. However, significantly higher values on the testosterone and cardiovascular variables, along with slight decreases in positive mood, were associated with the merit-based competition, but not the chance-based condition. In addition, an exploratory factorial analysis grouped the response components into two patterns traditionally related to more active or more passive behaviors. Thus, our results suggest that the perception of contributing to the outcome is relevant in the psychobiological response to competition in men. Overall, our results reveal the importance of the appraisal of control and causal attribution in understanding human competitive interactions.     

Effects of competition and season on survival and maturation of young bank vole females

In territorial microtines intra-specific density dependent processes can limit the maturation of individuals during the summer of their birth. This may have demographic consequences by affecting the number and the age distribution of breeding individuals in the population. Little is known about this process on a community level, though populations of many northern microtine species fluctuate in synchrony and are known to interfere socially with each other. We experimentally studied the influence of the field vole Microtus agrestis on maturation, breeding, space use and survival of weanling bank voles, Clethrionomys glareolus. Two additive competition experiments on bank vole populations were conducted in large outdoor enclosures, half of them additionally housing a field vole population. In a mid-summer experiment low population density and absence of older breeding females minimised intra-specific competition. Survival was not affected by the presence of field voles. Season had a significant effect on both the probability of maturation and breeding of the weanlings. Competition with field voles significantly delayed breeding, and coupled with seasonal effects decreased the probability of breeding. In a late-summer experiment breeding and survival of bank vole weanlings were studied for three weeks as part of a high density breeding bank vole population. Weanlings did not mature at all nor were their space use and survival affected by the presence of field voles. Our results show that competition with other species can also have an impact on breeding of immatures. In an extreme seasonal environment, even a short delay of breeding may decrease survival chances of offspring. Seasonal and competition effects together may thus limit the contribution of year born females to reproductive output of the population. Other studies have shown that adult breeding bank voles suffer lower survival in the presence of field voles, but this study showed no survival effects on the weanlings. Thus it might be beneficial for weanlings to stay immature especially in the end of the breeding season and postpone reproduction to the next breeding season if densities of competing species are high.     

Sexual competition and N supply interactively affect the dimorphism and competiveness of opposite sexes in Populus cathayana

Several important dioecious species show sexual spatial segregation (SSS) along environmental gradients that have significant ecological effect on terrestrial ecosystem. However, little attention has been paid to understanding of how males and females respond to environmental gradients and sexual competition. We compared eco‐physiological parameters of males and females of Populus cathayana under different sexual competition patterns and nitrogen (N) supply levels. We found that males and females interacting with the same or opposite sex showed significant differences in biomass partition, photosynthetic capacity, carbon (C) and N metabolism, and leaf ultrastructure, and that the sexual differences to competition were importantly driven by N supply. The intersexual competition was enhanced under high N, while the intrasexual competition among females was amplified under low N. Under high N, the intersexual competition stimulated the growth of the females and negatively affected the males. In contrast, under low N, the males exposed to intrasexual competition had the highest tolerance, whereas females exposed to intrasexual competition showed the lowest adaptation among all competition patterns. Sexual competition patterns and N supply levels significantly affected the sexual dimorphism and competitiveness, which may play an important role in spatial segregation of P. cathayana populations.     

Identifying critical interactions in complex competition dynamics between bean beetles

Identifying behavioural basis of competitive relationship is essential to understand outcome of interspecific competition. However, it remains difficult to investigate demographic effect of competitive behaviour, because various kinds of behaviours may co‐occur in the competition and make the dynamics far complicated in nonlinear ways. We report that the behavioural basis of interspecific interaction can be identified, by focusing on the timescale difference from the occurrence of each behaviour to the appearance of its demographic effect. Between two bean beetles, Callosobruchus chinensis and C. maculatus, major interspecific interactions are resource competition (RC) at the larval stage and reproductive interference (RI) at the adult stage. RC has longer time lag than RI, because effect of RC appears in the adult number of the next generation through larval competition while effect of RI appears instantaneously in the adult number through early death of females. If we detect two effects with different time lags from the competition dynamics, an effect with intergenerational time lag and with no time lag would be considered as RC and RI, respectively. We applied empirical dynamic modelling approach, which is a nonlinear time series analysis for detecting causal interactions and the strength, to two published datasets of experimental competition between those beetles. Results showed the significant causality from the winner species to the loser one in both experiments, but the causality time lag differed between experiments: the causality had no time lag in the C. chinensis‐win data, while intergenerational time lag in C. maculatus‐win data. Furthermore, detection of the causality with intergenerational time lag from C. maculatus to C. chinensis in both experiments suggests interplay of constant RC and variable RI which can reverse the outcome. This study is the first successful case study that links behavioural‐level interactions to demographic‐level effects in interspecific competition.