Density-dependent Growth Research Articles

Can controlled bow hunts reduce overabundant white-tailed deer populations in suburban ecosystems?

In the northern suburbs of NYC, land managers have begun implementing bow-only hunts to reduce overabundant white-tailed deer (Odocoileus virginianus) herds in an effort to promote forest regeneration. However, there have been no attempts to model the impact of bow hunting on deer population growth. Using harvest statistics from the Mianus River Gorge Preserve in Westchester County, NY we simulated the impact of bow hunting on a population of female deer exhibiting density-dependent growth and explored a range of carrying capacities, immigration rates, and harvest intensities. Simulated bow hunting (adult harvest≥1.8femaleskm−2) was capable of achieving deer densities believed necessary for forest regeneration (2.9femaleskm−2) in closed populations where carrying capacity=13.8femaleskm−2, representing the lower end of deer overabundance. At this carrying capacity and low immigration rates, the impact of bow hunting was more variable, producing population declines ranging from 20 to 70% contingent on harvest rates. Hours per harvest increased rapidly as the deer population declined requiring nearly 5 times the hourly effort as female density approached target levels. Sustaining harvests over multiple decades, particularly as effort per deer harvest increases, is one of the biggest challenges facing bow-only hunts. As controlled bow hunts are executed by volunteer sportsmen, reductions will be determined by hunters’ capacity or willingness to increase effort and efficiency. Bow hunting will therefore likely result in deer densities lower than historical peak values, yet higher than is currently assumed necessary for forest regeneration.

Outside-host growth of pathogens attenuates epidemiological outbreaks.

Opportunist saprotrophic pathogens differ from obligatory pathogens due to their capability in host-independent growth in environmental reservoirs. Thus, the outside-host environment potentially influences host-pathogen dynamics. Despite the socio-economical importance of these pathogens, theory on their dynamics is practically missing. We analyzed a novel epidemiological model that couples outside-host density-dependent growth to host-pathogen dynamics. Parameterization was based on columnaris disease, a major hazard in fresh water fish farms caused by saprotrophic Flavobacterium columnare. Stability analysis and numerical simulations revealed that the outside-host growth maintains high proportion of infected individuals, and under some conditions can drive host extinct. The model can show stable or cyclic dynamics, and the outside-host growth regulates the frequency and intensity of outbreaks. This result emerges because the density-dependence stabilizes dynamics. Our analysis demonstrates that coupling of outside-host growth and traditional host-pathogen dynamics has profound influence on disease prevalence and dynamics. This also has implications on the control of these diseases.

Mean Dosage Stimulation Range of Allelochemicals from Crude Extracts of Cucumis africanus Fruit for Improving Growth of Tomato Plant and Suppressing Meloidogyne incognita Numbers

Successful utilisation of allelochemicals in management of plant-parasitic nematodes depends on their degree of phytotoxicity. Conventional methods of determining phytotoxicity are tedious, with inconsistent results. Plants respond to increased dosages of allelochemicals in a density-dependent growth pattern, which allows the use of the Curve-fitting Allelochemical Response Data computer-based model to determine the mean dosage stimulation range of used allelochemicals. The CARD modelling was used to determine the stimulation range of fermented dried crude extracts of wild cucumber (Cucumis africanus) fruit for improving growth of tomato (Solanum lycopersicon) plants, each infested with 1500 eggs and juveniles of the southern root-knot (Meloidogyne incognita) nematode. Dilutions at 0, 2, 4, 8, 16, 32 and 64% were applied weekly through irrigation system. At 56 days after treatment, CARD demonstrated density-dependent growth patterns as dosages increased. The mean dosage stimulation range of diluted fermented crude extracts, computed from CARD biological indices, was 2.64% dilution for tomato plant. Since at 2% dilution, the material reduced final nematode population density of M. incognita by 90%. The 2.64% was suitable for stimulation of tomato plant and suppression of nematode numbers.

Density-dependent habitat use and growth of an estuarine fish

Density dependence can stabilize or destabilize population size through negative or positive feedback controls operating over different spatial and temporal scales. While many species have been shown to exhibit density dependence, the topic has received little attention in estuaries where environmental variability and larval supply are often considered to be the primary drivers of population dynamics. We used multiple long-term, fishery-independent data sets and a unique modeling approach to test the hypothesis that juvenile red drum ( Sciaenops ocellatus ) exhibit density-dependent habitat use and growth rates in estuaries in North Carolina, USA. Age-1 red drum exhibited density-dependent habitat use after accounting for environmental and landscape variables, disproportionately increasing northward and coastward in the study area at high abundance. Apparent individual growth rates of age-0 and age-1 red drum were generally negatively related to the abundance of their own age classes, but evidence of density-dependent growth rates for age-2 red drum was weak to nonexistent. Changes in spatial distribution of red drum when overall abundance was high did not overcome density-dependent effects on individual growth rates. Thus, density-dependent effects have potential negative feedbacks on population growth in estuaries and should not be ignored in future theoretical or empirical estuarine studies.

Quantification of non-isothermal, multi-phase crystallization of isotactic polypropylene: The influence of shear and pressure

Key issue in studying the crystallization process of semi-crystalline polymers, is the need for controlled (or known) boundary and initial conditions. Here dilatometry (PVT) is used to reveal the crystallization kinetics and the resulting morphology of isotactic polypropylene homopolymer as a consequence of the combination of non-isothermal cooling at elevated (isobaric) pressure and application of shear flow. Based on the flow strength the crystallization kinetics can be classified in three regimes; quiescent crystallization, flow enhanced point nucleation and flow-induced creation of oriented structures. Using ex-situ wide angle X-ray diffraction and small angle X-ray scattering we revealed the details of the (oriented) crystalline structures for the different regimes including the different phases (α-, β-, and γ-phase) that can occur in iPP. Some unique oriented structures of combined α- and γ-phase were found. The distribution of the crystal phase content is explained by the interplay of nucleation density and crystal phase dependent growth rate, which are functions of both temperature and pressure.

The bioenergetics of density-dependent growth in Arctic char (Salvelinus alpinus)

We explored the mechanisms of density-dependent growth in Arctic char ( Salvelinus alpinus ) by comparing the energetics of growth, consumption, and activity obtained under three replicated density treatments in a large-scale enclosure (90 m2surface area) experiment. The enclosures permitted the entry of zooplankton and allowed char to feed on the bottom and at the surface of the lake. We found a negative (power) relationship between growth and density. Char consumption rate decreased linearly with increasing density. Growth efficiency was affected by fish density in a similar manner as growth rate. Finally, activity increased with fish density and was particularly high at high densities. Our findings illustrate the complexity of the relationships among consumption, activity, growth rates, and fish density and bring further evidence to the possible involvement of behavioural mechanisms in density-dependent processes, notably by modulating activity costs with density.

Life-History and Spatial Determinants of Somatic Growth Dynamics in Komodo Dragon Populations

Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world’s largest lizard the Komodo dragon (Varanus komodoensis). The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture study at ten sites on four islands in eastern Indonesia, from 2002 to 2010. Generalized Additive Mixed Models (GAMMs) and information-theoretic methods were used to examine how growth rates varied with size, age and sex, and across and within islands in relation to site-specific prey availability, lizard population density and inbreeding coefficients. Growth trajectories differed significantly with size and between sexes, indicating different energy allocation tactics and overall costs associated with reproduction. This leads to disparities in maximum body sizes and longevity. Spatial variation in growth was strongly supported by a curvilinear density-dependent growth model with highest growth rates occurring at intermediate population densities. Sex-specific trade-offs in growth underpin key differences in Komodo dragon life-history including evidence for high costs of reproduction in females. Further, inverse density-dependent growth may have profound effects on individual and population level processes that influence the demography of this species.

Temporal variation in density dependent body growth of a large herbivore

Temporal variation both due to density dependent and density independent processes affect performance and vital rates in large herbivores. Annual fluctuations in climate affect foraging conditions and thus body growth of large herbivores during the short growing season in alpine habitats. Also, high animal densities on summer ranges may increase competition for food and reduce body mass gain. Yet, little is known about interactive effects of density and climate on alpine summer ranges, and the time scales these processes operate on. In this fully replicated landscape‐scale experiment, we kept domestic sheep at high and low densities over nine grazing seasons in an alpine habitat, and tested the relative role of density and annual variation for lamb body mass gain during summer and whether effects of density and annual variation interacted. We found that lambs at high density gained less mass over the summer season than lambs at low density. At short time scales the density effect interacted with annual fluctuations in body growth. We documented a long‐term temporal trend in body mass, consistent with the hypothesis that grazing effects affect habitat differentially at high and low density over years. At high density lamb autumn body mass declined during the first three grazing seasons and then stabilized, whereas body mass slightly increased over years at low density. This long‐term trend suggests accumulative density dependent effects from a biomass or quality reduction, and hence delayed food competition at high density and possibly facilitation at low density. Our experiment provides new insight into how density dependent effects on performance of a large herbivore depend on temporal scale of observation.

Density-Dependent Processes in the Life History of Fishes: Evidence from Laboratory Populations of Zebrafish Danio rerio

Population regulation is fundamental to the long-term persistence of populations and their responses to harvesting, habitat modification, and exposure to toxic chemicals. In fish and other organisms with complex life histories, regulation may involve density dependence in different life-stages and vital rates. We studied density dependence in body growth and mortality through the life-cycle of laboratory populations of zebrafish Danio rerio. When feed input was held constant at population-level (leading to resource limitation), body growth was strongly density-dependent in the late juvenile and adult phases of the life-cycle. Density dependence in mortality was strong during the early juvenile phase but declined thereafter and virtually ceased prior to maturation. Provision of feed in proportion to individual requirements (easing resource limitation) removed density dependence in growth and substantially reduced density dependence in mortality, thus indicating that ‘bottom-up’ effects act on growth as well as mortality, but most strongly on growth. Both growth and mortality played an important role in population regulation, with density-dependent growth having the greater impact on population biomass while mortality had the greatest impact on numbers. We demonstrate a clear ontogenic pattern of change in density-dependent processes within populations of a very small (maximum length 5 mm) fish, maintained in constant homogeneous laboratory conditions. The patterns are consistent with those distilled from studies on wild fish populations, indicating the presence of broad ontogenic patterns in density-dependent processes that are invariant to maximum body size and hold in homogeneous laboratory, as well as complex natural environments.

Population dynamics and control of invasiveSpartina alterniflora: inference and forecasting under uncertainty

Managing invaded ecosystems entails making decisions about control strategies in the face of scientific uncertainty and ecological stochasticity. Statistical tools such as model selection and Bayesian decision analysis can guide decision-making by estimating probabilities of outcomes under alternative management scenarios, but these tools have seldom been applied in invasion ecology. We illustrate the use of model selection and Bayesian methods in a case study of smooth cordgrass (Spartina alterniflora) invading Willapa Bay, Washington. To address uncertainty in model structure, we quantified the weight of evidence for two previously proposed hypotheses, that S. alterniflora recruitment varies with climatic conditions (represented by sea surface temperature) and that recruitment is subject to an Allee effect due to pollen limitation. By fitting models to time series data, we found strong support for climate effects, with higher per capita seedling production in warmer years, but no evidence for an Allee effect based on either the total area invaded or the mean distance between neighboring clones. We used the best-supported model to compare alternative control strategies, incorporating uncertainty in parameter estimates and population dynamics. For a fixed annual removal effort, the probability of eradication in 10 years was highest, and final invaded area lowest, if removals targeted the smallest clones rather than the largest or randomly selected clones. The relationship between removal effort and probability of eradication was highly nonlinear, with a sharp threshold separating -0% and -100% probability of success, and this threshold was 95% lower in simulations beginning early rather than late in the invasion. This advantage of a rapid response strategy is due to density-dependent population growth, which produces alternative stable equilibria depending on the initial invasion size when control begins. Our approach could be applied to a wide range of invasive species management problems where appropriate data are available.

Density-dependent regulation of year-class strength in age-0 juvenile striped bass (Morone saxatilis)

Abundance of age-0 striped bass ( Morone saxatilis ) exhibits 50-fold variability in Chesapeake Bay. Processes that act to reduce and thus regulate this variability were investigated. The potential for density-dependent regulation of growth and mortality in the early juvenile stage and its causes were investigated. Data from multiple seine and trawl surveys in upper Chesapeake Bay and tributaries were analyzed to construct growth and mortality indices having a high degree of spatial and temporal resolution. Age-0 mean lengths in September were inversely related to density, ranging from 67.8 mm in 1994, when mean density was 0.036·m–2, to 104.5 mm in 1992, when mean density was 0.003·m–2. Except for the Potomac River, evidence for density-dependent growth was consistent across subpopulations. Bioenergetics modeling indicated that prey consumption was limiting except in low-abundance years. Mortality increased with respect to abundance and also was density-dependent. The significant interaction between age-0 juvenile length in September and subsequent winter temperature on mortality indicated that density-dependent growth leads to size-selective overwinter mortality. A statistical model including age-0 abundances, age-0 lengths, and winter temperature explained a substantial fraction of variability and the mechanisms for regulation of striped bass recruitment.

Linking patterns and processes across scales: the application of scale-transition theory to algal dynamics on rocky shores

Understanding how species and environments respond to global anthropogenic disturbances is one of the greatest challenges for contemporary ecology. The ability to integrate modeling, correlative and experimental approaches within individual research programs will be key to address large-scale, long-term environmental problems. Scale-transition theory (STT) enables this level of integration, providing a powerful framework to link ecological patterns and processes across spatial and temporal scales. STT predicts the large-scale (e.g. regional) behavior of a system on the basis of nonlinear population models describing local (e.g. patch-scale) dynamics and the interaction between these nonlinearities and spatial variation in population abundance or environmental conditions. Here we use STT to predict the dynamics of turf-forming algae on rocky shores at Capraia Island, in the northwest Mediterranean. We developed a model of algal turf dynamics based on density-dependent growth that included the effects of local interactions with canopy algae. The model was parameterized with field data and used to scale up the dynamics of algal turfs from the plot scale (20×20 cm) to the island scale (tens of km). The interaction between nonlinear growth and spatial variance in cover of turfing algae emerged as a key term to translate the local dynamics up to the island scale. The model successfully predicted short-term and long-term mean values of turf cover estimated independently from a separate experiment. These results illustrate how STT can be used to identify the relevant mechanisms that drive large-scale changes in ecological communities. We argue that STT can contribute significantly to the connection between biomechanics and ecology, a synthesis that is at the core of the emerging field of ecomechanics.

Nonlinear effects of consumer density on multiple ecosystem processes

1. In the face of human-induced declines in the abundance of common species, ecologists have become interested in quantifying how changes in density affect rates of biophysical processes, hence ecosystem function. We manipulated the density of a dominant detritivore (the cased caddisfly, Limnephilus externus) in subalpine ponds to measure effects on the release of detritus-bound nutrients and energy. 2. Detritus decay rates (k, mass loss) increased threefold, and the loss of nitrogen (N) and phosphorus (P) from detrital substrates doubled across a range of historically observed caddisfly densities. Ammonium and total soluble phosphorus concentrations in the water column also increased with caddisfly density on some dates. Decay rates, nutrient release and the change in total detritivore biomass all exhibited threshold or declining responses at the highest densities. 3. We attributed these threshold responses in biophysical processes to intraspecific competition for limiting resources manifested at the population level, as density-dependent per-capita consumption, growth, development and case : body size in caddisflies was observed. Moreover, caddisflies increasingly grazed on algae at high densities, presumably in response to limiting detrital resources. 4. These results provide evidence that changes in population size of a common species will have nonlinear, threshold effects on the rates of biophysical processes at the ecosystem level. Given the ubiquity of negative density dependence in nature, nonlinear consumer density-ecosystem function relationships should be common across species and ecosystems.

Effect of Density on Growth and Survival of Young June Sucker

One of the fundamental determinants of survival and growth of individuals is population density. Typically, individuals exhibit negative density dependence, but positive density dependence (Allee effect) may occur. Understanding patterns of density dependence is important for conservation and management of species that have low densities as a result of recent population declines. June sucker (Chasmistes liorus) is an endangered species that was formerly abundant but now is found at low densities in Utah Lake. We tested the hypothesis that young June sucker exhibit positive density dependence (i.e., Allee effects) in growth and survival at low densities. In addition, we tested the hypothesis that patterns of density dependence in growth and survival of young June sucker are consistent across years. We conducted a series of 5 experiments in 5 separate years. All 5 experiments included similar levels of density manipulations of young June sucker. June sucker exhibited Allee effects in both growth and survival in some years, but patterns of density dependence varied widely among years. Growth exhibited consistent patterns of negative density dependence, especially at higher densities. Survival was less affected by density, exhibiting no response to density in about half of the experimental comparisons. Overall, intermediate densities around 50 individuals · m-2 seemed to provide the best tradeoff between growth and number produced.

Spatial and temporal scale of density-dependent body growth and its implications for recruitment, population dynamics and management of stream-dwelling salmonid populations

Density-dependent variations in body growth and size have important consequences for the population dynamics of stream-dwelling salmonid populations, since body size is related to a variety of ecologically relevant characteristics. These include survival and fecundity, competitive and predatory abilities, and foraging behavior. However, little work has been done to understand how density-dependent body growth varies across temporal and spatial scales and when this compensatory process is relevant for recruitment and population dynamics of stream- dwelling salmonids. Increased intra- or inter-cohort competition reduces growth rates of juveniles. Both within- and among-cohort differences at the juvenile stage are likely to be maintained through the lifetime. Limited movement or dispersal can lead to subdivision of a population into several local populations with independent dynamics. The spatial and temporal variation in movement and the patchy distribution of resources make fish likely to experience density- dependence across location, life-stage, and season. The relaxation of density-dependent suppression of body growth at low densities constitutes a potential mechanism for salmonids to persist in the face of environmental perturbation and may contribute to explaining the peculiar resilience to population col- lapses often showed by salmonids. The inclusion of density-dependent growth in population models may increase the usefulness of model predictions in management contexts. Models not accounting for density-dependent growth may underestimate the recovery potential of resident salmonid populations when they collapse to low densities.

Variability in the early life stages of juvenile plaice (Pleuronectes platessa) on west of Ireland nursery grounds: 2000–2007

Plaice (Pleuronectes platessa) are the most abundant juvenile flatfish present on west of Ireland nursery grounds. 0-group plaice were collected from eleven sandy beach nursery areas along the west coast of Ireland by beach seining (2000–2007). In the majority of years examined, certain beaches were found to support a higher abundance of juvenile plaice, or individuals that were larger in size and exhibited good condition, suggesting that differences in habitat quality exist between beaches. Monthly mean densities of plaice ranged from 2.4 (± 2.4) to 100 (± 1.3) individuals 1000 m−2. Mean lengths of plaice ranged between 6.0 (± 1.0) and 10.1 (± 0.5) cm. No evidence of density dependent growth was detected over the eight years of the study. The length and condition of juvenile plaice also differed between hauls, indicating the existence of microhabitat effects and emphasizing the importance of selecting an appropriate spatial resolution to adequately assess an area. Similar to other locations in Europe, juvenile plaice abundances on nursery grounds were inversely related to mean spring seawater temperatures during the pelagic stage. Abundances of 0-group plaice were not related to the number of either 1- or 2-group individuals collected during bottom-trawl surveys off the Irish west coast, demonstrating the difficulties associated with developing a recruitment index for plaice.

Ecologically and evolutionarily sustainable fishing of the pikeperch Sander lucioperca: Lake Oulujärvi as an example

Due to the multitude of participants and a diverse range of fishing gear used freshwater fisheries are often managed using minimum size limits (MSL) rather than regulations of total fishing effort. However, a concern has arisen whether attempts to improve ecological sustainability of fisheries by increasing MSLs would induce undesired adaptations to selective fishing. We examined the ecological and evolutionary impacts of varying fishing mortality rates under varying MSLs, with and without stockings, in an age-, size-, and maturity-structured evolutionary model which was parameterized for the Lake Oulujärvi pikeperch, Sander lucioperca. We found that at the current level of harvesting (fishing mortality rate, F = 0.7) and stockings (430 000 year −1), and under the assumption of strongly density-dependent growth, the nation-wide MSL of 370 mm maximizes theoretical biomass yield in a deterministic model but does not prevent severe recruitment overfishing under further increased fishing pressures or stochasticity in recruitment success. The recently imposed, local MSL of 450 mm better ensures stable yields, and even increases them if individual growth is density-independent, but further increase of MSL to 500 mm would already reduce yield especially if there was discard mortality for undersized fish. Given density-dependent growth, equal survival between wild and stocked fish, and sustainable fishing mortality rate, stockings do not increase yield or significantly improve the stability of yields. Evolutionarily stable size at maturation decreases under strong fishing mortality, but increased MSLs reduce the magnitude of this undesired effect. Negatively size-dependent natural mortality was found to have a positive effect on the otherwise negative selection for length-at-age. Increased MSLs also reduce the total selection for decreased length-at-age. Our results support the intentions to increase MSLs in order to improve both ecological and evolutionary sustainability of recreational fisheries.

Translocation of stream-dwelling salmonids in headwaters: insights from a 15-year reintroduction experience

Translocation programs are a common strategy to increase the number of viable populations of threatened freshwater fishes. Yet, only in a minority of cases the success or failure of translocations has been assessed through a quantitative analysis of demographic traits, compensatory responses, life-histories and population dynamics of the threatened species. A paradigmatic case a translocation program combining both management- and research-oriented activities is represented by the Marble Trout Conservation Program, which started in 1993 in the upper reaches of the Soca, Idirjca and Baca river basins (Slovenia) for the conservation of stream-dwelling marble trout Salmo marmoratus. In order to enhance the viability of the species, two new populations were created in 1996 by stocking 500 marble trout aged 1+ in previously fishless streams (Gorska and Zakojska) within the core habitat of the species. The new populations have been systematically monitored for 15 years by individually tagging and sampling marble trout. Our analyses show that deterministic extinction of marble trout populations are unlikely and that high-magnitude environmental stochasticity (i.e., severe floods) is the only main cause of local population extinction, despite the high resilience to flood-induced massive mortalities exhibited by marble trout through compensatory mechanisms (e.g., relaxation of density-dependent body growth and survival at low densities). Fishless headwaters, probably characterized by a history of recurrent severe floods, should not be considered as candidate sites for the creation of new populations. Fewer individuals than originally reintroduced (i.e., 500 fish aged 1+ in each stream) might be sufficient to establish viable populations, since compensatory mechanisms are likely to regulate population size around stream carrying capacity in a few years. Besides enhancing the species viability, translocation programs can provide an excellent framework for the estimation of ecological traits (e.g., life-histories, demography, population dynamics etc.), identify potential vulnerabilities and thus guide well-formed management actions for the threatened species.

Density-Dependent Growth in Juvenile Sockeye Salmon (OncorhynchusNerka)

Data gathered over 77 lake-years from 4 coastal British Columbia sockeye salmon nursery lakes suggest that density-dependent growth reductions are only possible at exceptionally high fry densities. In Great Central Lake (n=33 years) and Sproat Lakes (n=30 years) there was no relationship between smolt weight and mean summer fry densities ranging from 760-3800 fry ha -1 . However, in two years when Sproat Lake fry densities were unusually high (1983=5183 ha -1 , 1996=4801 ha -1 ) smolt weights were among the lowest recorded. In Woss and Vernon lakes (n=14 lake-years), there were significant bottom-up relationships between fall-fry weights and zooplankton biomass, but no relationships between December-fry weights and average fry densities (range 331-1361 ha -1 ), nor were there significant top-down relationships between fry densities and average zooplankton biomass. Comparisons of zooplankton production with bioenergetic-based fry consumption, suggested that the carrying capacity for Vernon Lake which had the highest rate of zooplankton production, was 12,700 fry ha -1 , and for Sproat Lake which had the lowest zooplankton production, was 5200 fry ha -1 . We conclude that fry densities in the range commonly observed for British Columbia coastal lakes (i.e. 500-4000 ha -1 ) cannot cause density-dependent reductions in prey biomass or fry growth rates. Further research is necessary.

Modelling responses of maize, millet and sorghum seedlings to crude extracts of Cucumis myriocarpus fruit as pre-emergent bio-nematicide

Biological indices generated using the CARD (curve-fitting allelochemical response data) model may be useful in crop-bio-nematicide interactions since they provide information related to the stimulation dosage of the material to the crops. The objective of this study was to determine: (1) Whether selected crops in the Gramineae family respond to crude extracts of Cucumis myriocarpus fruit in density-dependent patterns, and (2) the appropriate dosage of crude extracts of C. myriocarpus fruit when used as a pre-plant bio-nematicide in Gramineae family. Separate studies using three maize, millet and sorghum were conducted under greenhouse conditions with ten treatments (0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00 and 2.25 g material/pot), arranged in randomised complete block design, with five replicates. At harvest, 18 days after treatment, the CARD model demonstrated that the responses of plant organs when regressed on a series of crude extracts of C. myriocarpus fruit stimulate exhibited the density-dependent growth patterns, with various organs having different sensitivities to the material. The integrated sensitivity of the measured variables showed that the test crops differed with increasing order of sensitivity to the test material with increasing order of sensitivity to the material being sorghum > maize > millet. Estimated mean dosage response for stimulation (MDRS) for maize, millet and sorghum being 1.13, 0.86 and 1.12 g, respectively. In conclusion, at low dosages crude extracts of C. myriocarpus fruit stimulate plant growth and, therefore, have the potential for use as pre-emergent bio-nematicide in maize, millet and sorghum production. Key words: Biological indices, CARD model, density-dependent growth patterns, maize, millet, sorghum.