Current Population Density Research Articles

Wildlife as Insurance against Rainfall Fluctuations in a Semi-Arid Savanna Setting of Southeastern Zimbabwe

This paper presents modeling approaches for wildlife conservation in a semi-arid savanna setting where there are frequent occurrences of drought. The model was used to test the extent to which wildlife income offers opportunities to reduce fluctuations in income as a result of variations in annual rainfall. For the application of the model the wildlife and agro-pastoral systems of southeastern Zimbabwe were simulated. Results show that wildlife income has the potential to compensate for some of the losses in expected income from livestock during droughts. However, wildlife income becomes second best to irrigated agriculture in stabilizing income in areas that show highly fluctuating rainfall. Possible reasons for this include high costs of exploiting the wildlife resource, and the small fraction of wildlife revenues received by households and communities. In order to search for sustainable solutions in areas such as the southeastern low veld of Zimbabwe, it is also important to be aware that the current human population and livestock densities are far above current sustainable levels. Our results therefore suggest that current and future efforts to conserve biodiversity are doomed to fail if there are no efforts made to decongest areas surrounding parks of high densities of human and herbivore populations, and to let local households earn more revenues from wildlife.

Late Pleistocene climate change and the global expansion of anatomically modern humans

The extent to which past climate change has dictated the pattern and timing of the out-of-Africa expansion by anatomically modern humans is currently unclear [Stewart JR, Stringer CB (2012) Science 335:1317-1321]. In particular, the incompleteness of the fossil record makes it difficult to quantify the effect of climate. Here, we take a different approach to this problem; rather than relying on the appearance of fossils or archaeological evidence to determine arrival times in different parts of the world, we use patterns of genetic variation in modern human populations to determine the plausibility of past demographic parameters. We develop a spatially explicit model of the expansion of anatomically modern humans and use climate reconstructions over the past 120 ky based on the Hadley Centre global climate model HadCM3 to quantify the possible effects of climate on human demography. The combinations of demographic parameters compatible with the current genetic makeup of worldwide populations indicate a clear effect of climate on past population densities. Our estimates of this effect, based on population genetics, capture the observed relationship between current climate and population density in modern hunter-gatherers worldwide, providing supporting evidence for the realism of our approach. Furthermore, although we did not use any archaeological and anthropological data to inform the model, the arrival times in different continents predicted by our model are also broadly consistent with the fossil and archaeological records. Our framework provides the most accurate spatiotemporal reconstruction of human demographic history available at present and will allow for a greater integration of genetic and archaeological evidence.

Effects of Flow Regimes Altered by Dams on Survival, Population Declines, and Range‐Wide Losses of California River‐Breeding Frogs

Widespread alteration of natural hydrologic patterns by large dams combined with peak demands for power and water delivery during summer months have resulted in frequent aseasonal flow pulses in rivers of western North America. Native species in these ecosystems have evolved with predictable annual flood-drought cycles; thus, their likelihood of persistence may decrease in response to disruption of the seasonal synchrony between stable low-flow conditions and reproduction. We evaluated whether altered flow regimes affected 2 native frogs in California and Oregon (U.S.A.) at 4 spatial and temporal extents. We examined changes in species distribution over approximately 50 years, current population density in 11 regulated and 16 unregulated rivers, temporal trends in abundance among populations occupying rivers with different hydrologic histories, and within-year patterns of survival relative to seasonal hydrology. The foothill yellow-legged frog (Rana boylii), which breeds only in flowing water, is more likely to be absent downstream of large dams than in free-flowing rivers, and breeding populations are on average 5 times smaller in regulated rivers than in unregulated rivers. Time series data (range = 8 - 19 years) from 5 populations of yellow-legged frogs and 2 populations of California red-legged frogs (R. draytonii) across a gradient of natural to highly artificial timing and magnitude of flooding indicate that variability of flows in spring and summer is strongly correlated with high mortality of early life stages and subsequent decreases in densities of adult females. Flow management that better mimics natural flow timing is likely to promote persistence of these species and others with similar phenology.

CARACTERIZACIÓN DASOMÉTRICA Y DELIMITACIÓN DE RODALES DE MEZQUITE (Prosopis sp) EN EL ESTADO DE COAHUILA

Este estudio muestra las características dasométricas de rodales puros de mezquite (Prosopis sp) pre¬sentes en dos sitios de muestreo en el estado de Coahuila y que se caracterizan por su importancia en la producción de carbón; con ello se pretende conocer la densidad poblacional arbórea en la actualidad, además de la importancia ecológica del mezquite en los ecosistemas de la región. Se obtuvo un primer acercamiento del volumen de madera comercial disponible en los rodales de mezquite, además de la cartografía de la distribución del mezquite en el estado de Coahuila. Los resultados muestran que en el estado de Coahuila existen 73,868 ha cubiertas por rodales puros de mezquite y 3,803,149 ha son ocu¬padas por matorral desértico micrófilo, en el que también se desarrolla el género Prosopis. Los estudios dasométricos se llevaron a cabo en los municipios de Viesca y San Pedro de las Colonias, dando como resultados una densidad de población de 867 y 567 individuos/ha, respectivamente, un porcentaje de indi¬viduos comerciales de 35.23 y 27.84 % de manera respectiva y 1.64 y 39.71 m3•ha-1 de madera comercial.

The population dynamics and productivity of Acacia pennatula in the pasturelands of the Nature Reserve Mesas de Moropotente, Estelí, Nicaragua

Acacia pennatula trees are the most conspicuous woody species in the pasturelands of the Nature Reserve Mesas de Moropotente, Esteli, Nicaragua. Cattle ranchers keep A. pennatula because it produces fence posts, forage (pods) and firewood. A population projection matrix model was developed to: (1) estimate the sustainable harvest (H) of fence posts at different tree population densities, (2) explore the range of recruitment (R), and survival and growth of both saplings and small poles compatible with current population density, and (3) determine how much carbon is stored in the soil-pasture-tree system. Acacia pennatula trees take 40 years to reach H size (D30 ≥ 30 cm). Estimated sustainable H from current tree population density is 1.8l7 trees ha−1 year−1, yielding 2.8 large and 11.2 regular size fence posts ha−1 year−1. This annual output easily satisfies the needs of a typical 100 ha cattle ranch in the study area. Current population density is congruent with very low R (<100 saplings ha−1 year−1), very low survival rates (<0.30%) and/or retarded D30 growth of saplings and small poles. Total carbon in tree biomass was only 37 Mg ha−1. Cattle ranchers have learned to harness the invasive nature of the species to obtain valuable tree products for farm use or sale.

Population Status of the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) in Indiana

Abstract Studies that assess current and historical population densities accurately provide valuable information for management of wildlife species, particularly those in need of immediate conservation concern. The Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) has experienced drastic declines throughout its range during the previous few decades. This study documents its continued decline over the past 25 years in the last known remaining population in southern Indiana. We conducted mark–recapture surveys from June 2008 to October 2008 and July 2009 to September 2009 at 35 sites. Despite a considerable increase in effort over previous surveys, we documented fewer total captures and extremely low population densities. Density was estimated at 0.06 individuals/100 m2, and catch per unit effort was 0.05 individuals/person hour throughout the entire study area. This represents not only a significant decline in numbers from the historical study, but also is well below that reported for populat...

Human influence lowers plant genetic diversity in communities with extinction debt

Summary 1. Loss of plant species induced by adverse human influence and habitat fragmentation might be delayed due to a slow response to changed environmental conditions. This phenomenon is known as extinction debt, which can lead to the underestimation of actual threats to biodiversity. To adequately estimate the condition of recently fragmented plant communities and avoid future loss of species, good indicators of forthcoming extinctions are needed. 2. We studied the behaviour of genetic diversity of a relatively common habitat specialist grass Briza media in fragmented calcareous grasslands in which the extinction debt has been previously documented. Species richness in this system is shown to be determined by historical landscape patterns and human population densities prevailing centuries ago. We hypothesize that genetic diversity in this grassland system is related to current landscape patterns and contemporary human impact since genetic diversity might react more quickly to environmental changes than species diversity. 3. In contrast to species diversity, genetic diversity was indeed best described by current connectivity of grasslands. Additionally, genetic diversity was negatively related to current human population density, indicating an adverse effect of contemporary human settlements on studied species. The faster response of genetic diversity to changed environmental conditions compared to species richness was further supported by the absence of an expected correlation between species richness and genetic diversity. 4. Human population density a century ago had a positive effect on genetic diversity. A similar effect has been demonstrated for species richness in these grasslands, indicating that traditional land use in the past has supported the development of both genetic and species diversity. 5. Synthesis. Genetic diversity of Briza media in fragmented communities is reacting quickly to changes in landscape structure and anthropogenic pressure. Our results confirm that plant species can be prone to genetic deterioration due to habitat fragmentation and negative anthropogenic impact even if the decline in species richness has been delayed by extinction debt. Thus, a decrease of population genetic diversity in fragmented communities can be taken as the first indication of future species losses.

Effects of sika deer on vegetation in Japan: A review

The Japanese sika deer Cervus nippon has expanded its range by nearly 70% during the last two decades. Browsing by sika deer affects vegetation in both agricultural and forested habitats. Effects of sika deer on vegetation are conspicuous on deer-inhabited islands: forest structure and composition are altered by deer grazing and browsing, and consequently regeneration is prevented. By felling of old trees, forest gaps are formed, but since sapling recruitment is prevented, shade intolerant plants invade. Unpalatable forbs like ragwort Senecio cannabifolius and ferns like bracken Pteridium aquilinum (Dennstaedtiaceae) become dominants in open habitats. At the places of highest deer density, the Zoysia japonica community, a low growing grass mat, develops. Sika deer function as a seed dispersal agent of this grass. Indirect effects of sika deer are not well studied, but some studies have shown reduction of understory bamboo cover, which in turn improves the survival of tree seedlings and declines of wood mice Apodemus spp. Japanese forests in lower mountainous areas were widely logged during the 1940s and 1950s. These areas were not well planted during the war and until 1950, but thereafter intensively planted to alter to conifer plantation as a nationwide campaign. For several decades after the war, rodents and hares grazed planted trees. According to growth of the planted trees to form canopy, which is unfavorable for rodents and hares, their damage declined. After the 1960s, old-growth forests in high mountainous areas were logged, and conifers were planted. Animals causing forestry damage were replaced by sika deer during the 1980s. Sika deer eat a wide variety of foods, and are gregarious, which causes heavy impacts on vegetation. Effects of sika deer are expanding to natural forests, alpine vegetation, and marshes. To reduce damages on forestry and natural vegetation, as many as 100,000 sika deer are culled every year. However, the hunter population is rapidly declining, and it is expected population control by culling will be insufficient. Although sika deer are an important component of Japanese forests, current population densities exceed the capacity of many ecosystems to tolerate herbivory.

The coincidence of biodiversity patterns and human settlement in Africa

AbstractIn spite of high loss of biodiversity in landscapes converted to farmland or urban areas, a positive correlation exists between species richness and endemism and human population density at coarse spatial scales. Data representing precolonial and contemporary human population patterns in Africa were overlaid on species distribution data covering 4080 vertebrate species. Species richness tracks both the precolonial and the current human population density. Areas of high vertebrate endemism are particularly closely associated with precolonial population centres. This suggests that patterns of population growth in Africa were, more than today, governed by factors that also enhanced local species persistence and speciation. The traditional conservation focus on wilderness areas with few people, and generally rather low endemism, needs to be complemented with strategies for sustainable development in some of the densely populated areas.

Patterns of genetic diversity in outcrossing and selfing populations ofArabidopsis lyrata

Arabidopsis lyrata is normally considered an obligately outcrossing species with a strong self-incompatibility system, but a shift in mating system towards inbreeding has been found in some North American populations (subspecies A. lyrata ssp. lyrata). This study provides a survey of the Great Lakes region of Canada to determine the extent of this mating system variation and how outcrossing rates are related to current population density, geographical distribution, and genetic diversity. Based on variation at microsatellite markers (progeny arrays to estimate multilocus outcrossing rates and population samples to estimate diversity measures) and controlled greenhouse pollinations, populations can be divided into two groups: (i) group A, consisting of individuals capable of setting selfed seed (including autogamous fruit set in the absence of pollinators), showing depressed outcrossing rates (T(m) = 0.2-0.6), heterozygosity (H(O) = 0.02-0.06) and genetic diversity (H(E) = 0.08-0.10); and (ii) group B, consisting of individuals that are predominantly self-incompatible (T(m) > 0.8), require pollinators for seeds set, and showing higher levels of heterozygosity (H(O) = 0.13-0.31) and diversity (H(E) = 0.19-0.410). Current population density is not related to the shift in mating system but does vary with latitude. Restricted gene flow among populations was evident among all but two populations (F(ST) = 0.11-0.8). Group A populations were more differentiated from one another (F(ST) = 0.78) than they were from group B populations (F(ST) = 0.59), with 41% of the variation partitioned within populations, 47% between populations, and 12% between groups. No significant relationship was found between genetic and geographical distance. Results are discussed in the context of possible postglacial expansion scenarios in relation to loss of self-incompatibility.

Home Range and Population Density of Fishers in Eastern Ontario

Abstract: Fishers (Martes pennanti) were almost extirpated in Ontario, Canada, south of the French and Mattawa rivers by the 1940s but have recolonized much of their former range over the past several decades. We assessed the effect of the current harvest quota on a fisher population in eastern Ontario by estimating home range size and population density from a sample of radiocollared animals. Mean (± SD) adult home ranges (based on annual 95% min. convex polygons) were consistently smaller than those reported in the literature (M: 11 ± 4.4 km2; F: 2.1 ± 0.8 km2), with up to 71% overlap of adjacent intrasexual home ranges. This yielded an estimated adult fisher population density of 32.7/100 km2 of suitable habitat, as defined by the habitat composition within observed home ranges. We further estimated that between 2003 and 2005, trappers harvested 17.8‐42.3% of the pretrapping population. These results suggest that although current fisher population density is high in our study area compared to reported densities in other areas, harvest rate is also high and an increase in quota is unwarranted.

Grassland diversity related to the Late Iron Age human population density

1 Species-rich semi-natural grasslands in Europe developed during prehistoric times and have endured due to human activity. At the same time, intensive grassland management or changes in land use may result in species extinction. As a consequence, plant diversity in semi-natural calcareous grasslands may be related to both historical and current human population density. 2 We hypothesize that current vascular plant diversity in semi-natural calcareous grasslands is positively correlated with the Late Iron Age (c. 800-1000 years ago) density of human settlements (indicated by Late Iron Age fortresses and villages) due to enhancement of grassland extent and species dispersal, and negatively correlated with current human population density due to habitat loss and deterioration. 3 We described the size of the community vascular plant species pool, species richness per 1 m(2) and the relative richness (richness divided by the size of the species pool) in 45 thin soil, calcareous (alvar) grasslands in Estonia. In addition to historical and current human population density we considered simultaneously the effects of grassland area, connectivity to other alvar grasslands, elevation above sea level (indicating grassland age), soil pH, soil N, soil P, soil depth, soil depth heterogeneity, geographical east-west gradient, precipitation and spatial autocorrelation. 4 Both the size of the community species pool and the species richness are significantly correlated with the Late Iron Age human population density. In addition, species richness was unimodally related to the current human population density. The relative richness (species 'packing density') was highest in the intermediate current human population densities, indicative of moderate land-use intensity. 5 Community species pool size decreased non-linearly with increasing soil N, and was highest at intermediate elevation. Small-scale richness was greater when sites were well connected and when the elevation was intermediate. Spatial autocorrelation was also significant for both species pool size and small-scale richness. 6 In summary, human land-use legacy from prehistoric times is an important aspect in plant ecology, which could be an important contributor to the current variation in biodiversity. (Less)

Harvesting control in an integrodifference population model with concave growth term

We consider the harvest of a certain proportion of a population that is modeled by an integrodifference equation, which is discrete in time and continuous in the space variable. The dispersal of the population is modeled by an integral of the growth function evaluated at the current population density against a kernel function. A concave growth function is used. In our model, growth occurs first, then dispersal and lastly harvesting control before the next generation. With the goal of maximizing the discounted profit stream, the optimal control is characterized by an optimality system. Illustrative examples are computed numerically.

Activity patterns of reintroduced lion Panthera leo and spotted hyaena Crocuta crocuta in the Addo Elephant National Park, South Africa

AbstractAfrica's large predator guild competes for a limited food resource base. To minimize the degree of competition, we hypothesized that the two largest members of this guild and its fiercest competitors, the lion and the spotted hyaena, would partition their activity patterns to avoid interacting. We used 96‐h continuous follows of focal animal(s) to determine when the six radio‐collared lions and eight radio‐collared spotted hyaenas, reintroduced into Addo Elephant National Park in 2003/2004, were active using a binomial measure of activity which was defined as movements &gt;100 m during each hourly period. Contrary to our predictions, lions and hyaenas did not partition their activity times, probably because of their current low population densities. Both species exhibited a crepuscular activity pattern although hyaenas were far less active during daylight. A sub‐adult lioness minimized competitive interactions by becoming diurnal. This is likely to be a common strategy for lions that have been expelled from their natal pride to become nomadic, as it allows them to minimize kleptoparasitic and agonistic interactions from competitively dominant conspecifics and competitors. The increase in testosterone that occurs in males upon reaching sexual maturity, darkens their pelage and causes them to be more directly impacted by the heat, and thereby affords females an opportunity to escape from males during hot temperatures. Similarly, the longer pelage of young hyaenas restricts their activity to the cooler night‐time.

Population size and density of Colobus vellerosus at the Boabeng‐Fiema Monkey Sanctuary and surrounding forest fragments in Ghana

The Boabeng-Fiema Monkey Sanctuary (BFMS) is inhabited by a growing population of Ursine colobus (Colobus vellerosus), a species that is listed as vulnerable. Smaller, degraded forest fragments that surround the BFMS also contain C. vellerosus and may provide an important habitat for the monkeys. Our objectives were to 1) determine the current population size and density of C. vellerosus at BFMS and in five surrounding fragments, 2) examine the differences in demographics between the fragments and BFMS, and 3) determine whether a relationship exists between population density and fragment size and isolation distance from BFMS. The census was a complete count and was conducted for 1 month (July 2003) by S.W. and trained research assistants. Seven census routes were walked simultaneously on 13 days. The 2003 population estimate of C. vellerosus at BFMS was 217-241 individuals (15 groups), a slight increase from the 2000 census. Numbers in the fragments (58-62, six groups) have remained stable since 1997, when the only other census of these fragments was conducted. Mean group size did not differ between the fragments and BFMS. Larger fragments had larger numbers of colobus, but there was no relationship between fragment size and colobus density. Isolation distance had no effect on population density. Our data suggest that colobus probably travel between fragments. Conservation efforts should focus on treating the small forests and their connecting areas as a single conservation unit.

Market Hunting in the Taï Region, Côte d’Ivoire and Implications for Monkey Populations

We studied the effect of market hunting on primate species in the Tai National Park and adjacent forests in Cote d’Ivoire. We assessed the impact of hunting by comparing the calculated maximal reproduction rate with the current off-take rate. We assessed the average bushmeat consumption per capita/per year from weekly investigations on bushmeat available in 88 bushmeat restaurants and markets over a 12-mo period in 1999. We derived data on preferences for particular game species from interviews of 162 bushmeat consumers, 25 subsistence hunters and 3 groups of professional hunters. Hunting pressure was highest on the larger primate species such red colobus (Procolobus badius), black- and- white colobus (Colobus polykomos) and sooty mangabeys (Cercocebus atys). The amount of primate bushmeat extracted from the Tai National Park and surrounding forests was 249,229 kg in 1999. We estimated population densities using line transect surveys. By referring to current population densities we calculated the maximum production of each species using the Robinson Redford model (2001) and assuming unhunted conditions. A comparison of current harvest levels with maximum production suggests that harvest of Procolobus badius is sustainable, whereas current off-take of Colobus polykomos, Cercocebus atys, Cercopithecus diana (diana monkey) and C. campbelli (Campbell’s monkeys) exceeds sustainability by ≤3 times. We recommend that wildlife managers promote programs that encourage the production of domestic animals as a substitute for wild meat.

Territorial behaviour and population dynamics in red grouse Lagopus lagopus scoticus. II. Population models

Summary Recent experiments on cyclic red grouse populations discovered that aggressiveness, induced by testosterone implants, depressed population density for more than a year after the implants were exhausted. This confirms the observation, also made in previous studies of this territorial species, that aggressiveness can determine population density. Additionally, it hints at a form of social memory that sustains the effect of episodes of high aggressiveness after their cause has ceased to exist. We explore the logical consequences of this observation with a simple model of the interaction between population density and aggressiveness. A flexible function describes how aggressiveness changes from year to year as a function of population density. At low densities animals are tolerant to conspecifics and aggressiveness falls from one year to the next. Conversely, at high densities aggressiveness rises. In the model, current aggressiveness is set by aggressiveness in the previous year, and modified by last year's population density (first version) or by current population density (second version). We assume no particular behavioural mechanism underlying this process but derive conditions under which changes in aggressiveness, effected by density, can generate unstable dynamics. The two versions of the model give fluctuations that differ in period and amplitude but have similar conditions for unstable dynamics. Specifically, the more abrupt the transition from tolerant to intolerant behaviour with increasing density, the more likely are cycles to occur. We show how a previous model of the kinship hypothesis for red grouse cycles can be recast in the current terminology, and how the new models offer a more general way of examining red grouse population dynamics.

Factors influencing deer browsing damage to red spruce ( Picea rubens) seedlings in coastal red spruce–balsam fir stands of southwestern Nova Scotia

The impact of deer browsing on the distribution and growth of naturally regenerating red spruce seedlings established within recently harvested and mature, coastal red spruce–balsam fir stands was evaluated. More specifically, we examined browsing frequency and severity in relation to distance from forest cover, stand age, and seedling height. Relative height increment and condition of browsed (20% removal of total biomass) and non-browsed seedlings after one growing season were also compared. A significant distance×stand age interaction was observed for browsing frequency, largely the result of differences among recently harvested stands. Browsing damage within mature stands was negligible, but when occurring, was restricted to taller seedlings within 20 m of the forest edge. Eleven percent of all seedlings within harvested stands were browsed, with seedlings between 50 and 100 cm tall being preferred. Most of the seedlings (92%) sustained less than 30% biomass removal. Fifty-two percent of these seedlings experienced less than 10% biomass loss. Relative height increase of browsed seedlings was significantly reduced. Most seedlings were able to recover from clipping damage, regaining much of the initial height and biomass originally lost by the end of summer. Seedling condition was not detrimentally affected by the clipping rate, although overall biomass gain of affected seedlings was lower. If no further browsing damage is sustained, biomass increment may be delayed by approximately one growing season, relative to undamaged seedlings of equal size and established under similar micro-environmental conditions. Current population densities of deer appear to have minimal impacts on re-establishment of coastal red spruce–balsam fir stands in southwestern Nova Scotia. Low impacts may be due to high seedling densities, as more than adequate numbers of seedlings remained untouched throughout the harvested stands.

Effects of temperature on performance and phenotypic selection on plant traits in alpine Ranunculus acris.

Discovering temperature effects on the performance of tundra plants is important in the light of expected climate change. In this 4-year study on alpine Ranunculus acris, I test the hypothesis that temperature influences flowering phenology, reproductive success, growth, population dynamics, and phenotypic selection on quantitative traits, by experimental warming using open-top chambers (OTCs). Warming significantly advanced flowering phenology in only one season. Seed number and weight were significantly increased by warming during the first three seasons, but not in the fourth. Plants inside OTCs produced bigger leaves than control plants in the fourth season, but leaf number was unaffected by the OTC treatment. Despite increased seed number and weight, the density of flowering plants decreased inside OTCs compared to control plots, possibly because of a higher graminoid cover inside OTCs. Phenotypic-selection regression showed a significant selection differential and gradient in the direction of larger leaf sizes in control plants, whereas no selection on leaf size was detected on warmed plants. The direction and strength of selection on flowering time, flower number, and leaf number did not differ between control and warmed plants. The results suggest that increased reproductive output of R. acris may not be sufficient to maintain current population density under a denser vegetation cover.

Interactions between Operophtera brumata and Tortrix viridana on oak: new evidence from time‐series analysis

1. Yearly population estimates of the green oak leaf roller moth, Tortrix viridana (Lepidoptera: Tortricidae), and the winter moth, Operophtera brumata (Lepidoptera: Geometridae), were taken from the pedunculate oak, Quercus robur, from 1951 to 1966 in Wytham Woods, Oxfordshire, U.K. Larval mortality from parasitoids was recorded for both species over the same period.2. Operophtera brumata population density fluctuated around a constant mean, whereas T. viridana population density exhibited a linear decline over the sampling period. Population counts were subjected to time‐series analysis after the linear decline was removed from the T. viridana data by detrending. Multiple regression models were built so that variation in the per capita rate of increase of each population could be partitioned among (a) current and previous population density, (b) current and previous population density of the second moth species, and (c) rates of larval parasitism.3. Multiple regression analysis suggested that variation in the per capita rate of increase of O. brumata could be explained by negative feedback from O. brumata density at T–2 (32%), a negative relationship with T. viridana density at T–1 (18%), and a positive relationship with parasitism suffered by T. viridana at T–1 (24%).4. The T. viridana population time‐series was dominated by a rapid feedback process such that per capita rate of increase at time T was negatively related to population density at time T–1, explaining 53% of variance in population growth rate. Per capita rate of increase was unrelated to larval parasitism or densities of O. brumata.5. In light of previous life‐table and experimental studies on O. brumata and T. viridana, the current analyses suggest that pupal predation (data not presented) and interspecific competition are significant determinants of O. brumata population growth rates in Wytham Woods. In contrast, T. viridana population growth rates appear to be dominated by rapid negative feedback consistent with intraspecific competition.