Population dynamics of three songbird species in a nestbox population in Central Europe show effects of density,climate and competitive interactions

Unravelling the contributions of density‐dependent and density‐independent factors in determining species population dynamics is a challenge, especially if the two factors interact. One approach is to apply stochastic population models to long‐term data, yet few studies have included interactions between density‐dependent and density‐independent factors, or explored more than one type of stochastic population model. However, both are important because model choice critically affects inference on population dynamics and stability. Here, we used a multiple models approach and applied log‐linear and non‐linear stochastic population models to time series (spanning 29 years) on the population growth rates of Blue Tits Cyanistes caeruleus, Great Tits Parus major and Pied Flycatchers Ficedula hypoleuca breeding in two nestbox populations in southern Germany. We focused on the roles of climate conditions and intra‐ and interspecific competition in determining population growth rates. Density dependence was evident in all populations. For Blue Tits in one population and for Great Tits in both populations, addition of a density‐independent factor improved model fit. At one location, Blue Tit population growth rate increased following warmer winters, whereas Great Tit population growth rates decreased following warmer springs. Importantly, Great Tit population growth rate also decreased following years of high Blue Tit abundance, but not vice versa. This finding is consistent with asymmetric interspecific competition and implies that competition could carry over to influence population dynamics. At the other location, Great Tit population growth rate decreased following years of high Pied Flycatcher abundance but only when Great Tit population numbers were low, illustrating that the roles of density‐dependent and density‐independent factors are not necessarily mutually exclusive. The dynamics of this Great Tit population, in contrast to the other populations, were unstable and chaotic, raising the question of whether interactions between density‐dependent and density‐independent factors play a role in determining the (in) stability of the dynamics of species populations.     

Direct negative density‐dependence in a pond‐breeding frog population

Understanding population dynamics is critical for the management of animal populations. Comparatively little is known about the relative importance of endogenous (i.e. density‐dependent) and exogenous (i.e. density‐independent) factors on the population dynamics of amphibians with complex life cycles. We examined the potential effects of density‐dependent and ‐independent (i.e. climatic) factors on population dynamics by analyzing a 15‐yr time series data of the agile frog Rana dalmatina population from Târnava Mare Valley, Romania. We used two statistical models: 1) the partial rate correlation function to identify the feedback structure and the potential time lags in the time series data and 2) a Gompertz state‐space model to simultaneously investigate direct and delayed density dependence as well as climatic effects on population growth rate. We found evidence for direct negative density dependence, whereas delayed density dependence and climate did not show a strong influence on population growth rate. Here we demonstrated that direct density dependence rather than delayed density dependence or climate determined the dynamics of our study population. Our results confirm the findings of many experimental studies and suggest that density dependence may buffer amphibian populations against environmental stress. Consequently, it may not be easy to scale up from individual‐level effects to population‐level effects.     

Optimal management of the rare Gladiolus imbricatus in Estonian coastal meadows indicated by its population structure

Questions: What is the best grassland management regime for the threatened plant species Gladiolus imbricatus; is the stage structure of local populations a feasible indicator of the effect of changed management. Location: Coastal meadow system in southwestern Estonia. Methods : The effect of five management regimes was studied in a long‐term (three‐year) field experiment: (1) mowing in late July, (2) grazing by cattle, (3) grazing by sheep, (4) sheep grazing during the first year and mowing during subsequent years, (5) no management (control). Results: The population density increased significantly in response to the mowing treatment and to the mowing after sheep grazing treatment. The proportion of grazed plant individuals was higher in the sheep‐grazed than in the cattle‐grazed treatment. Generative and vegetative adult individuals of G. imbricatus were significantly more damaged by cattle herbivory than juveniles. All management regimes shifted the population structure towards a dynamic state where juvenile stages dominate, while the not managed control retained a regressive population structure. Conclusions: Population stage structure was a useful indicator of different management conditions, even in the case where population density did not differ. As indicated by population stage structure, the best management regime for G. imbricatus was either mowing in late July only, or alternation of grazing and mowing in different years.     

Strong “bottom‐up” influences on small mammal populations: State‐space model analyses from long‐term studies

“Bottom‐up” influences, that is, masting, plus population density and climate, commonly influence woodland rodent demography. However, “top‐down” influences (predation) also intervene. Here, we assess the impacts of masting, climate, and density on rodent populations placed in the context of what is known about “top‐down” influences. To explain between‐year variations in bank vole Myodes glareolus and wood mouse Apodemus sylvaticus population demography, we applied a state‐space model to 33 years of catch‐mark‐release live‐trapping, winter temperature, and precise mast‐collection data. Experimental mast additions aided interpretation. Rodent numbers in European ash Fraxinus excelsior woodland were estimated (May/June, November/December). December–March mean minimum daily temperature represented winter severity. Total marked adult mice/voles (and juveniles in May/June) provided density indices validated against a model‐generated population estimate; this allowed estimation of the structure of a time‐series model and the demographic impacts of the climatic/biological variables. During two winters of insignificant fruit‐fall, 6.79 g/m² sterilized ash seed (as fruit) was distributed over an equivalent woodland similarly live‐trapped. September–March fruit‐fall strongly increased bank vole spring reproductive rate and winter and summer population growth rates; colder winters weakly reduced winter population growth. September–March fruit‐fall and warmer winters marginally increased wood mouse spring reproductive rate and September–December fruit‐fall weakly elevated summer population growth. Density dependence significantly reduced both species' population growth. Fruit‐fall impacts on demography still appeared after a year. Experimental ash fruit addition confirmed its positive influence on bank vole winter population growth with probable moderation by colder temperatures. The models show the strong impact of masting as a “bottom‐up” influence on rodent demography, emphasizing independent masting and weather influences; delayed effects of masting; and the importance of density dependence and its interaction with masting. We conclude that these rodents show strong “bottom‐up” and density‐dependent influences on demography moderated by winter temperature. “Top‐down” influences appear weak and need further investigation.     

Landscape context influences the abundance of amphibians and the strength of their food web interactions in small ponds

Many species, including most amphibians, undergo an ontogenetic niche shift (ONS) from an aquatic larval stage to a terrestrial adult stage. We use the ratio of aquatic to terrestrial habitat in a landscape as a tool to understand the influence of landscape context on the population growth of ONS species. The aquatic to terrestrial ratio (ATR) of habitats can be viewed as an analog to the influence of resource ratios on the population growth of consumers and depends on the degree to which each habitat type limits the growth of a given population. Population growth rates of shorter‐lived species tend to be more limited by demographic rates in early (aquatic) life stages. As a result, increasing the ATR should lead to a higher total population size in the landscape (and higher densities in the terrestrial habitat), but have little influence on the density of individuals in any given aquatic habitat. Alternatively, population growth rates of longer‐lived species tend to be more limited by demographic rates in later (terrestrial) life stages and increasing the ATR should have little influence on the total population size in the landscape, but decrease the density of individuals in any given aquatic habitat. We show that among‐landscape variation in the breeding‐pond densities of three widespread amphibians with contrasting life histories is consistent with this framework. Within‐pond densities of Pseudacris crucifer, a species with short‐lived adults, were not influenced by ATR, whereas within‐pond densities of Hyla versicolor, a longer‐lived member of the same family (Hylidae), declined as ATR increased. Ambystoma maculatum, a long‐lived salamander, also had lower densities in ponds with higher ATR. Because A. maculatum larvae are important predators in ponds, we use structural equation modeling to show that landscape context (ATR) can moderate community structure via direct (amphibian abundances) and indirect (prey species richness) effects.     

Inorganic nitrogen source for autotrophic growth of Euglena mutabilis Schmitz

The effect of inorganic nitrogen source on population growth of Euglena mutabilis, an acidophillic benthic protozoa colonizing on the sediment of acid mine drainage, was investigated. Sodium nitrate, ammonium chloride, and ammonium sulfate were tested as nitrogen sources. The population density of E. mutabilis at equilibrium density cultivated in ammonium chloride‐ and ammonium sulfate‐containing media was 9–11 times higher than that in sodium nitrate‐containing medium at the optimal salt medium concentration. The population growth of E. mutabilis in ammonium sulfate‐containing medium was rapid and reached half of the equilibrium density after ca. 228 h, which was ca. 77 h earlier than that in ammonium chloride‐containing medium. Culture medium with ammonium sulfate as the nitrogen source achieved the highest maximum population density and the fastest growth rate among the three nitrogen salts used as nitrogen sources.     

Population dynamics of Northern Gannets in North America, 1984–2009

Northern Gannet (Morus bassanus) colonies (N = 6) in North America have been regularly censused since the late‐1960s. Monitoring populations of a top‐predator like gannets provides insight into possible changes in the marine environment and contributes to an understanding of their demography. We report the results of aerial censuses of gannet colonies conducted from 1984 to 2009. Standard methods were used and involved making high‐quality photographs of colonies from a fixed‐wing aircraft, and subsequently counting apparently occupied sites (AOS) in the photographs. As of 2009, the breeding population of gannets in North America was estimated to be 116 825 pairs, or ～27% of the world population. From 1984 to 2009, the population grew at an average rate of 4.4% per annum and this growth was likely the result of continued population recovery after acute persecution in the past. Growth rates began to slow during the latter part of our study, likely due to density‐dependent effects and reductions in food availability. Despite the growth of the North American gannet population, gannets have not established new colonies, possibly because populations had been so depressed that growth could be accommodated within existing colonies.     

SEASONAL CHANGES IN SIZE STRUCTURE OF SARGASSUM AND TURBINARIA POPULATIONS (PHAEOPHYCEAE) ON TROPICAL REEF FLATS IN THE SOUTHERN RED SEA1

Seasonal variation in density, thallus length and biomass, population size structure, and allometric length‐biomass relationships was investigated in populations of Sargassum ilicifolium (Turner) C. Agardh, Sargassum subrepandum (Forssk.) C. Agardh, and Turbinaria triquetra (J. Agardh) Kütz. (Phaeophyceae) on shallow reef flats in the southern Red Sea. Thallus length and biomass varied strongly with season, with the highest values occurring in the cooler months. Thallus densities showed no significant temporal variation. Log‐total biomass versus log‐density relationships were positive throughout the growth season without any decrease in the slope of the relationship. In two populations, biomass‐density combinations approached the interspecific biomass‐density line, but the massive annual shedding of modules occurred before self‐thinning would set in. Allometric length‐biomass relationships varied with season in all populations and were associated with seasonal module initiation, growth, and shedding. Evidence of a strong asymmetric competition was found in two high‐density populations. These populations showed a predominance of small thalli during peak development, asymmetrical Lorenz curves, increasing Gini coefficients, and increasing thallus length relative to biomass during the main growth phase. In two other less crowded populations, small thalli were absent during peak development, Lorenz curves were symmetrical, and Gini coefficients decreased during the main growth phase. In these populations, size equalization appears to be due to responses at the modular level rather than size‐dependent mortality. We conclude that changes in size structure in this highly seasonal environment are determined by module dynamics, modified by asymmetric competition in some populations, with a minor role of recruitment and no regulatory effect of self‐thinning.     

Dynamics of springtail and mite populations: the role of density dependence, predation, and weather

Abstract 1. Ecological theory suggests that density‐dependent regulation of organism abundance will vary from exogenous to endogenous factors depending on trophic structure. Changes in abundance of soil arthropods were investigated at three trophic levels, springtails (Collembola), predaceous mites (Acari), and macro‐arthropods (spider, adult and larval beetles, centipedes). Predictions were that springtails are predator regulated and mites are food limited according to the Hairston et al. (1960) model, which predicts alternating regulation by competition and predation from fungi to springtails to mites to macro‐arthropods. The alternate hypothesis was based on the bottom‐up model of trophic dynamics, which predicts that each trophic level is regulated by competition for resources. 2. The relative contributions to springtail and mite population dynamics of endogenous (i.e. density‐dependent population growth related to food availability) and exogenous (i.e. predation and weather) factors were tested using time‐series analysis and experimental manipulation of water conditions. Box patterns were distributed within an aspen forest habitat located in the Canadian prairies and surveyed weekly from May to September 1997–1999. Each box depressed the leaf litter, creating a microhabitat island for soil arthropods that provided counts of invertebrates located immediately beneath the boxes. 3. Strong evidence was found for endogenous control of springtail and mite numbers, indicated by a reduction in population growth related to density in the previous week. Contrary to predictions, no evidence was found for regulation of springtail numbers by mites, or for regulation of mite numbers by macro‐arthropods. Springtail population growth rate was related positively to current springtail density (8 and 23% variation explained) and related negatively to 1‐week lagged density (85 and 58%), and related negatively to temperature (5 and 5%) for time‐series data and for experimental addition of water respectively. Mite population growth rate was related positively to current mite density (54%) and temperature (4%), and negatively to 1‐week lagged mite density (20%) and precipitation (6%) for time‐series analysis. For experimental addition of water, mite growth rate was related positively to current mite density (44%) and temperature (5%), and negatively to 1‐week lagged density (11%). Results differed from the Hairston et al. (1960) model predictions but were consistent with a bottom‐up view that springtail and mite populations were regulated intrinsically by competition for food and secondarily by temperature as a function of reproduction.     

Effects of larval density on a natural population of Culex restuans (Diptera: Culicidae): no evidence of compensatory mortality

1. This study investigated the effects of strong density dependence on larval growth, development, and survival of the mosquito Culex restuans (Theobald). It also tested the hypothesis that density reduction early in larval development could result in as many or more individuals surviving to adulthood (compensation or over‐compensation, respectively), or increased reproductive performance via rapid development and greater adult size. 2. In a field study of a natural population of C. restuans, the effects of a 75% lower density on percentage survivorship to adulthood, number of adults, development time, adult size, adult longevity, and size dependent fecundity were tested. 3. No evidence was found of compensation or over‐compensation in adult production, or of effects of lower density on percentage survivorship. Low density yielded significant increases in adult size, adult longevity, and size‐dependent fecundity, and a decrease in development time. 4. Estimated per‐capita population growth rate was significantly greater in the low‐density treatment than in the high‐density treatment. It is inferred that this difference was due to greater per‐capita resources, which increased female size and fecundity, and reduced development time. Greater per‐capita population growth could therefore result from early mortality of larvae, meaning that the hydra effect, which predicts greater equilibrium population with, as opposed to without, extrinsic mortality, may be possible for these mosquitoes.     

Forest Fragmentation Alters the Population Dynamics of a Late‐successional Tropical Tree

Tropical late‐successional tree species are at high risk of local extinction due to habitat loss and fragmentation. Population‐growth rates in fragmented populations are predicted to decline as a result of reduced fecundity, survival and growth. We examined the demographic effects of habitat fragmentation by comparing the population dynamics of the late‐successional tree Poulsenia armata (Moraceae) in southern Mexico between a continuous forest and several forest fragments using integral projection models (IPMs) during 2010–2012. Forest fragmentation did not lead to differences in population density and even resulted in a higher population‐growth rate (λ) in fragments compared to continuous forests. Habitat fragmentation had drastic effects on the dynamics of P. armata, causing the population structure to shift toward smaller sizes. Fragmented populations experienced a significant decrease in juvenile survival and growth compared to unaltered populations. Adult survival and growth made the greatest relative contributions to λ in both habitat types during 2011–2012. However, the relative importance of juvenile survival and growth to λ was highest in the fragmented forest in 2010–2011. Our Life Table Response Experiment analysis revealed that positive contributions of adult fecundity explained most of the variation of λ between both habitats and annual periods. Finally, P. armata has a relatively slow speed of recovery after disturbances, compromising persistence of fragmented populations. Developing a mechanistic understanding of how forest fragmentation affects plant population dynamics, as done here, will prove essential for the preservation of natural areas.     

Dynamics of an introduced population of mouflon Ovis aries on the sub‐Antarctic archipelago of Kerguelen

A commonly reported pattern in large herbivores is their propensity to irrupt and crash when colonizing new areas. However, the relative role of density‐dependence, climate, and cohort effects on demographic rates in accounting for the irruptive dynamics of large herbivores remains unclear. Using a 37‐yr time series of abundance in a mouflon Ovis aries population located on Haute Island, a sub‐Antarctic island of Kerguelen, 1) we investigated if irruptive dynamics occurred and 2) we quantified the relative effects of density and climate on mouflon population dynamics. Being released in a new environment, we expected mouflon to show rapid growth and marked over‐compensation. In support of this prediction, we found a two‐phase dynamics, the first phase being characterised by an irruptive pattern best described by the θ‐Caughley model. Parameter estimates were r_m=0.29±0.005(maximum growth rate), K=473±45 (carrying capacity) and S=2903±396 (surplus) mouflon. With a θ=3.18±0.69 our model also supported the hypothesis that density dependence is strongest at high density in large herbivores. The second phase was characterised by an unstable dynamics where growth rate was negatively affected by population abundance and winter precipitation. Climate, however, did not trigger population crashes and our model suggested that lagged density‐dependence and over‐grazing were the probable causes of mouflon irruptive dynamics. We compare our results with those of Soay sheep and discuss the possibility of a reversible alteration of the island carrying capacity after the initial over‐grazing period.     

Influence of host density and population structure on egg production in the coccidophagous ladybird,Chilocorus nigritus F. (Coleoptera: Coccinellidae)

1 Studies on aphidophagous coccinellids have indicated that patch quality, and, in particular, the age structure of the prey or the phenological age of the plant, may play an important role in stimulating oviposition behaviour. However, little is known about the egg‐laying tactics of coccidophagous species. 2 When restricted to a single, large colony of overlapping generations of their diaspid host Abgrallaspis cyanophylli (Signoret), adult females of the coccidophagous ladybird Chilocorus nigritus F. varied their egg production rate in a cyclic pattern that lasted for approximately 22 days. This information was used to generate hypotheses relating to eliciting cues for oviposition. 3 Two experiments were carried out in the absence of conspecific larvae to assess: (i) whether changes in host density at levels above those needed to sustain egg production in the females affected egg output and (ii) the effect of restricting beetles to various homogeneous prey population structures on daily egg production. 4 Changes in host density caused a significant but transient decline in egg production whereas a heterogeneous prey population elicited significantly higher levels of oviposition than homogeneous ones with similar host densities, irrespective of the growth stage of the prey. 5 Beetles were fed to satiation throughout the experiments but the data obtained suggest that cues for eliciting oviposition operated in a density‐dependent fashion. The results of the study are used to discuss the possibility that visual and chemical cues are quantitatively used by ovipositing beetles to assess patch suitability.     

Demography of three dominant sedges under contrasting grazing regimes in the High Arctic

Abstract. Tiller demography of Carex aquatilis ssp. stans, Carex membranacea, and Eriophorum angustifolium ssp. triste was investigated in ungrazed and grazed high arctic vegetation on central Ellesmere Island, Canada. Tiller birth, growth, flowering and death were studied from excavated clonal fragments, and tiller density and biomass were studied from excavated turfs. Five life‐cycle stages were determined: dormant buds, juvenile, mature, flowering and dead tillers. A stage‐based transition matrix model was developed to estimate the long‐term dynamics of the sedge populations and to compare life‐history strategies between ungrazed and grazed populations. Short‐term and retrospective models, based on the growth during the sampling year and during the lifetime of the clonal fragments, respectively, were compared to see how well the short‐term model can describe demography of long‐lived plants. According to the short‐term model, tiller populations were decreasing (λ < 1 except for C. membranacea), whereas the retrospective model indicated that the tiller populations were increasing. Tiller population growth rates did not differ between ungrazed and grazed habitats. Nevertheless, the similar growth rates may be obtained by balanced differences in the vital rates between plants of the two habitats. The plants in the ungrazed habitat tended to remain in their current life‐cycle stage, whereas plants in the grazed habitat moved quickly to the next stage and died earlier. C. aquatilis ssp. stans appears to gain a competitive advantage over the other species under intensive grazing, as indicated by the higher tiller density and greater below‐ground biomass in grazed vegetation. The greater amount of below‐ground biomass apparently buffers C. aquatilis ssp. stans against grazing better than the other species.     

Growth forms of Leymus chinesis (Poaceae) at the different developmental stages of the natural population

The manner in which the density of Leymus chinensis increases from a single plant to a dominant population can be understood by tracing the development of a population from early to late stages. Parent shoot density, above‐ground dry weight, spike density, heading rate and spike dry weight, density of spreading shoots (buds/daughter shoots in apical/axillary rhizomes) and clumping shoots (buds/daughter shoots in axillary parent shoots), and young rhizome length and weight were investigated in the same quadrats for a low density/early stage (LE) population and a high density/late stage (HL) population. Clonal growth (buds/daughter shoots formation) and sexual reproduction (spikes formation) increased while rhizome storage (young rhizome weight) decreased during the transition from LE to HL. In a LE population an outward occupation strategy was employed, with a high proportion of spreading shoots. As the population density gradually increased until HL, an inward consolidation strategy increasing shoot amount in previously occupied areas, was adopted. This was characterized by a high proportion of clumping shoots. Interestingly, the trade‐off between spreading and clumping shoots can be adjusted by the duration of young rhizome elongation during a growth season. In other words, compared with a HL population, a LE population shortened the duration of young rhizome elongation during the growth season, which resulted in more time for the production of axillary spreading shoots along the rhizomes, and high amounts and proportions of total spreading shoots. The special growth patterns, that is, trade‐offs among growth forms, allow L. chinensis to establish dominant populations throughout the eastern Eurasian Steppe.     

Dynamics of an age‐structured population drawn from a random numbers table

I constructed age‐structured populations by drawing numbers from a random numbers table, the constraints being that within a cohort each number be smaller than the preceding number (indicating that some individuals died between one year and the next) and that the first two‐digit number following 00 or 01 ending one cohort’s life be the number born into the next cohort. Populations constructed in this way showed prolonged existence with total population numbers fluctuating about a mean size and with long‐term growth rate (r) ≈ 0. The populations’ birth rates and growth rates and the females’ per capita fecundity decreased significantly with population size, whereas the death rates showed no significant relationship to population size. These results indicate that age‐structured populations can persist for long periods of time with long‐term growth rates of zero in the absence of negative‐feedback loops between a population’s present or prior density and its birth rate, growth rate, and fecundity, contrary to the assumption of density‐dependent regulation hypotheses. Thus, a long‐term growth rate of zero found in natural populations need not indicate that a population’s numbers are regulated by density‐dependent factors.     

Influence of occupation history and habitat on Washington sea otter diet

Habitat characteristics are primary determinants of nearshore marine communities. However, biological drivers like predation can also be important for community composition. Sea otters (Enhydra lutris ssp.) are a salient example of a keystone species exerting top‐down control on ecosystem community structure. The translocation and subsequent population growth and range expansion of the northern sea otter (Enhydra lutris kenyoni) in Washington State over the last five decades has created a spatio‐temporal gradient in sea otter occupation time and density, and acts as a natural experiment to quantify how sea otter population status and habitat type influence sea otter diet. We collected focal observations of sea otters foraging at sites across the gradient in varying habitat types between 2010 and 2017. We quantified sea otter diet composition and diversity, and long‐term rates of energy gain across the gradient. We found that sea otter diet diversity was positively correlated with cumulative sea otter density, while rate of energy gain was negatively correlated with cumulative density. Additionally, we found that habitat type explained 1.77 times more variance in sea otter diet composition than sea otter cumulative density. Long‐term diet studies can provide a broader picture of sea otter population status in Washington State.     

FINE‐SCALE GENETIC STRUCTURE IN A WILD BIRD POPULATION: THE ROLE OF LIMITED DISPERSAL AND ENVIRONMENTALLY BASED SELECTION AS CAUSAL FACTORS

Individuals are typically not randomly distributed in space; consequently ecological and evolutionary theory depends heavily on understanding the spatial structure of populations. The central challenge of landscape genetics is therefore to link spatial heterogeneity of environments to population genetic structure. Here, we employ multivariate spatial analyses to identify environmentally induced genetic structures in a single breeding population of 1174 great tits Parus major genotyped at 4701 single‐nucleotide polymorphism (SNP) loci. Despite the small spatial scale of the study relative to natal dispersal, we found multiple axes of genetic structure. We built distance‐based Moran's eigenvector maps to identify axes of pure spatial variation, which we used for spatial correction of regressions between SNPs and various external traits known to be related to fitness components (avian malaria infection risk, local density of conspecifics, oak tree density, and altitude). We found clear evidence of fine‐scale genetic structure, with 21, seven, and nine significant SNPs, respectively, associated with infection risk by two species of avian malaria (Plasmodium circumflexum and P. relictum) and local conspecific density. Such fine‐scale genetic structure relative to dispersal capabilities suggests ecological and evolutionary mechanisms maintain within‐population genetic diversity in this population with the potential to drive microevolutionary change.     

Effects of doubled atmospheric CO2 concentration on the growth and photosynthesis of Chlamydomonas reinhardtii (Volvocales, Chlorophyceae)

The freshwater microalga, Chlamydomonas reinhardtii Dangeard, was cultured under 350 and 700 ppmv CO₂ to determine the impact of doubled atmospheric CO₂ concentration on its growth and photosynthesis. No significant difference was observed in the specific growth rate, photosynthetic efficiency, maximal net photo‐synthetic rate and light‐saturating point between the low and high CO₂ cultures. Both the low‐ and high‐CO₂‐grown cells showed reduced light‐dependent O₂ evolution rate and photochemical efficiency (F_v/F_m) owing to photoinhibition when exposed to high photon flux density. However, high‐CO₂‐grown cells were less photoinhibited, and showed better recovery in dim light or darkness during the initial period of the recovery process.