This research note builds upon a number of important articles published in a variety of outlets concerning the population ecology of interest groups. Importantly, Lowery and Gray (1995), Nownes (2004), and Nownes and Lipinski (2005) empirically demonstrated the dependence on the density of pre-existing, similar groups when predicting new group formations. In this letter, I add to this research by modeling the density of ideologically divergent reproductive rights groups as well as offer supporting evidence for the popular Energy-Stability-Area model. The former is a novel consideration in the field of population ecology which primarily examines ideologically similar groups. I show that density dependence is at play among these polarized groups. I also provide insight into counter-mobilization movements of group formation by empirically demonstrating which groups are initial movers versus reactionary formers. In doing so, I raise important questions for researchers concerned with the emergence, longevity, and impact of interest groups over long periods of time. Finally, this research provides some insight into the expectations of group formation behavior in light of the landmark Dobbs decision.

The establishment of plants in an ecosystem is limited by the availability of seeds and the availability of suitable sites for establishment. Describing plant population dynamics through the relative strength of seed and establishment limitation is an important concept in the study of natural ecosystems. To date, it is unclear whether this concept can be applied to describe populations of annual weeds in agricultural fields. Using a recruitment function, we show that limitation parameters prove valuable in describing seedling recruitment in weed populations. We conducted a seed addition experiment in three cornfields (Zea mays L.) and recorded seedling recruitment in populations of the economically important weed barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. Seed predation, competition with other weeds, and seed burial were prevented. We estimated the strength of seed and establishment limitation in the population with two parameters: n, which is the number of microsites, and b, which is the suitability of those sites to support a seedling. We further estimated the relative proportions of density-dependent and density-independent establishment limitation in the seedling population. Recruitment rates of E. crus-galli ranged from 31% to 36% across all evaluated seed densities and fields, which is high compared with results from other seed addition studies. Two of the three monitored populations were predominantly establishment limited at the highest evaluated seed density of 2,400 added seeds m−2. Further knowledge about the relative strength of limitations in other weed populations will provide important information on how effective different weed management strategies can be.

The cryptic nature and lack of consistent biological control of the stem fly, Melanagromyza sojae Zehntner, an emerging pest of soybean, Glycine max (L.) Merrill, necessitated the monitoring and assessment of the impact of the parasitoid complex on seasonal regulation of the pest population. In this paper, we measure and relate, using the host density as a predictor variable, the seasonal density dependence of M. sojae parasitoids and the level of parasitism in soybean fields. The results revealed density dependence of parasitioids. The populations built up concomitant with the host insect, reached their peak during the mid-season, and declined towards the end of the crop season. A complex of 10 species of hymenopteran parasitoids comprising six species from Pteromalidae and one species each from the families Eurytomitidae, Eucoilidae, Braconidae and Eulopidae had a significant impact on M. sojae populations with a peak parasitism of ~50%. The seasonality and relative abundance of parasitoids were explored. Eurytoma sp. (Eurytomitidae) and Gronotoma sp. (Eucoilidae) were the most prevalent parasitoids throughout the season, whereas the pteromalid Sphegigaster sp. was dominant during the mid-season. The modulation of management practices aimed at conservation of these bioagents could improve the biological control of M. sojae populations. We discuss the practicality of several management options aimed at achieving this goal.

Theory and models of crop yield loss from weed competition have led to decision models to help growers choose cost-effective weed management. These models are available for multiple-species weed communities in a single season of several crops. Growers also rely on crop rotation for weed control, yet theory and models of weed population dynamics have not led to similar tools for planning of crop rotations for cost-effective weed management. Obstacles have been the complexity of modeling the dynamics of multiple populations of weed species compared to a single species and lack of data. We developed a method to use limited, readily observed data to simulate population dynamics and crop yield loss of multiple-species weed communities in response to crop rotation, tillage system, and specific weed management tactics. Our method is based on the general theory of density dependence of plant productivity and extensive use of rectangular hyperbolic equations for describing crop yield loss as a function of weed density. Only two density-independent parameters are required for each species to represent differences in seed bank mortality, emergence, and maximum seed production. One equation is used to model crop yield loss and density-dependent weed seed production as a function of crop and weed density, relative time of weed and crop emergence, and differences among species in competitive ability. The model has been parameterized for six crops and 15 weeds, and limited evaluation indicates predictions are accurate enough to highlight potential weed problems and solutions when comparing alternative crop rotations for a field. The model has been incorporated into a decision support tool for whole-farm management so growers in the Central Great Plains of the United States can compare alternative crop rotations and how their choice influences farm income, herbicide use, and control of weeds in their fields.

Concern over the consequences of increased weed seed inputs to the soil seed bank during the transition period from conventional to organic production is one obstacle to grower adoption of reduced input and nonchemical weed management strategies. An 11-yr study was established in southwest Montana to investigate the effect of a single pulse of wild oat seeds on subsequent seed bank dynamics. In 1993, wild oat seeds were sown at five densities (0, 20, 80, 320, and 800 seeds m−2) in eight wheat–small grain cropping systems that differed in the number of crops in rotation and fallow periods. Wild oat seed banks were measured each spring from 1994 to 2004 in half of the cropping systems and from 2001 to 2004 in all eight systems. In 1994, seed bank densities in response to the pulse were as much as 11 times higher than controls that received no seeds in 1993. By 1996, after mechanical fallowing of all cropping systems, wild oat seed bank densities were not significantly different from densities in control plots regardless of the size of the initial seed pulse and remained so through 2004. These data suggest that increases in wild oat seed inputs during the organic transition period will have relatively few long-term agronomic effects on the dynamics of wild oat seed banks in these systems. In addition, wild oat seed banks may be constrained by factors other than cropping sequence when herbicides are not used, such as possible density-dependent regulation as a result of increased soil pathogen attack and seed predation.

Bioeconomic models are predicated upon the relationship between weed fecundity and crop yield loss in consecutive growing seasons, yet this phenomenon has received few empirical tests. Residual effects of wild proso millet (WPM) fecundity in sweet corn upon WPM seedling recruitment, weed management efficacy, and crop yield within a subsequent snap bean crop were investigated with field experiments in Urbana, IL, in 2005 and 2006. WPM fecundity in sweet corn showed strong positive associations with WPM seedbank density, seedling recruitment, and demographic transitions within snap bean. A negative exponential relationship between WPM initial seedling density and seedling survival of a single rotary hoe pass indicated that the rotary hoe was ineffective at low weed population densities, but its efficacy increased with increasing weed population density to a maximum of 75% seedling mortality. Efficacy of postemergent chemical control of WPM was unaffected by WPM population density. Path analysis models demonstrated dependence between WPM fecundity in sweet corn, WPM seedling recruitment in snap bean, and reductions in snap bean yield in subsequent growing season, mediated by negative impacts of WPM seedling establishment on snap bean stand. These results underscore the importance of expanding integrated weed management programs to include management of annual weed populations both at the end of their life cycle, by reducing fecundity and seed survival, and at the very beginning of their life cycle, by reducing seedling recruitment and establishment.

Species interactions are often context-dependent, where outcomes require an understanding of influences among multiple biotic and abiotic factors. However, it remains unclear how abiotic factors such as temperature combine with important biotic factors such as density-dependent food limitation and predation to influence species interactions. Using a native grassland – grasshopper – wolf spider model food chain in tallgrass prairie, we conducted a manipulative field experiment to examine how predator–prey interactions respond to manipulations of temperature, grasshopper density, and food chain length. We find that grasshopper performance responses to temperature and predator treatments were density dependent. At high densities, grasshopper survival decreased with increased temperature when no spiders were present. When spiders were present, grasshopper survival was reduced, and this effect was strongest in the cooled treatment. In contrast, grasshopper survival did not vary significantly with spider presence or among temperature treatments at low grasshopper densities. Our results indicate that context-dependent species interactions are common and highlight the importance of understanding how and when key biotic and abiotic factors combine to influence species interactions.

Previous work has highlighted increased opportunities for the transmission of Syngamus trachea within pheasant release pens, due in part to high levels of environmental contamination around communal areas. Despite this, the distribution of adult worms within their definitive hosts is not significantly different from predicted distributions under Taylor's power law. Therefore, density-dependent processes are probably acting to regulate S. trachea population dynamics. Patterns of nematode fecundity were investigated in a semi-naturally occurring population of ring-necked pheasants (Phasianus colchicus) and a wild population of carrion crows (Corvus carone). Worm length was a reliable indicator of nematode fecundity, and a negative association between mean worm length and mean worm burden was identified within both the species. The stunting of worms at greater parasite densities was present in both immunologically naïve and previously exposed pheasants, so is unlikely to be a function of age-dependent acquired immunity. Interestingly, the effect of parasite crowding in the crow population explained more of the variation in mean worm length, apparently driven by a greater mean worm burden when compared with pheasants. The findings of the present study suggest that fecundity is a function of parasite density, i.e. parasite-mediated competition and not host-mediated heterogeneities in immunocompetence.

South-East Asian tropical rain forests experience sporadic, but profuse, seed production after general flowering, leading to the synchronous emergence of various seedlings and subsequent seedling dynamics, which play a crucial role in determining species distribution and coexistence. We examined the relative importance of both biotic (initial height, conspecific seedling density) and abiotic (canopy openness, per cent sand, soil water content) drivers using survival data for 1842 seedlings of 12 dipterocarp species for 1.5 y following mast fruiting in an old-growth Bornean tropical rain forest. More than 30% of all dipterocarp seedlings survived 1.5 y after mast fruiting. When all species were analysed together, we found that initial seedling height, canopy openness and conspecific seedling density affected dipterocarp seedling survival. Negative density dependence indicated that predators were not satiated, but dipterocarp seedlings rather suffered from host-specific natural enemies or intraspecific competition. Species-level analyses of seven dipterocarp species showed large variation in response to biotic and abiotic factors. These results suggest that interspecific differences in the relative importance of biotic and abiotic effects on seedling survival might contribute to species coexistence.

The effective floral neighbourhood is the radius around a plant where the density of flowering plants and other factors affect visitation rates and pollination success of plants. This study aims to determine this radius and focuses on the effects of conspecific plant density, plant sex and the amount of shrub vegetation on visitation rates of Clusia blattophila, a dioecious bush pollinated by Amazonina platystylata cockroaches. The number of visits did not differ between flower sexes but cockroaches spent less time on the rewardless female flowers. The density effect was scale dependent. The distribution of flowering individuals within the 15-m radius had a significant positive effect on flower visitation rates. At a larger scale (35–45-m radius), an increase in density of male plants led to a decrease in visitation rates, indicating competition for pollinators. Within the smaller radius, the facilitative effect was probably induced by elevated floral advertisement and high mobility of cockroaches at this scale. Within the larger radii, the results indicated that cockroach mobility was restricted and population density was stable at this scale. Density of male plants affected visitation rates because only male plants reward pollinators. Hence, male plants were the true competitors.

This article reviews the adequacy of data and models currently being used to estimate the present and future population sizes of the Antarctic toothfish (Dissostichus mawsoni Norman) in the Ross Sea regional ecosystem. The current tagging programme is unlikely to provide an accurate picture of total population size, and estimates of both the pre-exploitation spawning stock biomass and the ratio of current to pre-exploitation biomass are unreliable. Many parameters necessary for estimating future population growth or decline have not been measured, and the current objective of a 50% reduction in biomass relative to unexploited biomass may easily fail to prevent a much larger reduction from taking place. The need to guess values of important parameters makes it impossible to set bounds on the potential errors of population forecasts. Current scientific knowledge is far from what is needed to predict the likely effects of food-web responses to harvesting of toothfish in the Ross Sea, or to predict the feedback effects of those food-web changes on toothfish populations.

We assessed seedling dynamics and understorey light before and after a hurricane in five randomly selected 5 × 5-m subplots, within 30 permanent sample plots covering a total area of 3750 m2 in a lower montane wet tropical forest, Jamaica over a period of 3 y. Understorey light increased (≈ 60%) following the passage of Hurricane Dean in 2007 but decreased in 2009. Overall, seedling density was positively related to light and survivorship was positively related to both light and density. Mortality was significantly lower and most species recorded their highest growth when the canopy was open (2007–2008). However, lower diversity during this period coincided with higher (average) mortality of uncommon species. The hurricane altered the relative importance of interactions between light, seedling density and dynamics. Consequently, interactions were significant before or 2 y after but not 1 y after the hurricane and their significance varied among the years and species. Periodic changes in the importance of these interactions and the effects of the hurricane were used to separate 12 common species along a continuum of responses, which ranged from positive (lower mortality), neutral to negative (lower growth). Our results indicate that hurricanes have positive and negative effects on seedling dynamics; therefore an increase in the intensity and frequency of hurricanes will likely alter seedling composition, and hence forest structure.

The Argentine stem weevil (Listronotus bonariensis) was an economically important pest in New Zealand pastures until the release of the parasitoid Microctonus hyperodae. This contribution uses historical data to investigate the regulation of the pest populations prior to, and somewhat during, the establishment of this parasitoid in dryland Canterbury, New Zealand. Thus, a significant goal of this study is to provide an L. bonariensis population dynamics baseline for any future work that aims to analyse the full effects of M. hyperodae on the weevil, now that equilibrium with the weevil host has been reached.

The population dynamics of L. bonariensis, based on a life-table approach, were investigated using data collected regularly for eight years from populations in Canterbury, New Zealand. The key factor affecting end-of-season L. bonariensis density was found to be variation in second generation fourth instar prepupal and pupal mortality. This may have been caused by arrested development and ongoing mortality resulting from the onset of cooler autumnal conditions.

A compensatory response was found in recruitment to the second summer weevil generation, whereby the realised fecundity of the emergent first summer generation of weevils was found to be negatively related to the density of adult weevils per ryegrass tiller. This is the first time that this has been found via long-term population analysis of L. bonariensis, although indications of this have been found elsewhere in caging, pot and small plot experiments.

In this study, the effect of the parasitoid biocontrol agent Microctonus hyperodae on L. bonariensis population dynamics was unclear, as the analysis covered a period when the parasitoid Microctonus hyperodae was introduced and still establishing. It does, however, raise important questions for future analysis in terms of the interaction between parasitism and unrealised fecundity.

The results in this contribution also highlighted regional differences. Overwintering mortality of adult weevils in Canterbury was constant between years, whilst earlier studies in the North Island Waikato region indicated this mortality was density dependent. In addition, the availability of tillers in endophyte-free ryegrass pastures in Canterbury had no influence on egg and early-instar larval survival, which contrasts with the finding from endophytic Waikato pastures.

We studied the effect of density of larvae on pre-imaginal development in 2 flea species (Xenopsylla conformis and Xenopsylla ramesis) parasitic on 2 desert rodent species (Dipodillus dasyurus, adult body mass 20 g and Meriones crassus, 80 g). We predicted a decrease in duration of development with an increase in density of larvae. In general, in both flea species, duration of larva-to-pupa development decreased with an increasing larval density. In addition, this stage of development was longer in male fleas and in fleas from parents fed on D. dasyurus. The effect of larval density on larval development was manifested mainly when parent fleas fed on D. dasyurus. Duration of pupation decreased with increasing larval density only in offspring of fleas fed on G. dasyurus. In both fleas, pupation was longer in males. The effect of parent host on duration of pupation was found in X. ramesis only (longer if the host was M. crassus). Resistance of newly emerged fleas to starvation depended mainly on parent host species. Young X. conformis survived longer if their parents fed on D. dasyurus, whereas young X. ramesis survived longer if their parents fed on M. crassus. It was also found that (a) an individual flea that spent more time as a larva also spent more time as a pupa and (b) longer larval development resulted in a shorter time that a newly emerged flea was able to survive when starved.

Aggregative responses are commonly observed in insects, including chrysomelids, affecting both individual and population growth rates. In two closely related chrysomelid beetles (Galerucella calmariensis and G. pusilla) feeding on purple loosestrife (Lythrum salicaria), recent studies suggest that male-produced pheromones may cause both inter- and intraspecific attraction. This paper further examines the causes and consequences of feeding aggregations in these species. Olfactometer studies confirm previous findings, showing cross-species attraction to damaged plants, but suggest that also damaged induced plant volatiles may be involved. In addition, the studies suggest that the cross-species attraction observed in previous studies have asymmetric effects on the two beetles. Galerucella pusilla was more attracted to damage by G. calmariensis than to damage by conspecifics. Laboratory and field data suggest that feeding aggregations in these species increase pupal mass, at least at low to intermediate larval densities. This positive feedback may have important consequences for the spatiotemporal dynamics and as a consequence on the role of the two chrysomelid beetles on biological control of purple loosestrife.

In order to study the impact of fishing on a grouper population, we propose in this paperto model the dynamics of a grouper population in a fishing territory by using structuredmodels. For that purpose, we have integrated the natural population growth, the fishing,the competition for shelter and the dispersion. The dispersion was considered as aconsequence of the competition. First we prove, that the grouper stocks may be lesssensitive to the removal of large male individuals if female population are totallyprotected. Second, we show that fishing does not disturb the demographic structure of thepopulation. Finally, we prove that female selective fisheries have the potential ofdrastically reduce reproductive rates. We also prove that male fishing decreasescompetition and then increases the total population number.

The Near Threatened white rhinoceros Ceratotherium simum went extinct in Botswana during the 20th century because of poaching. Several attempts have been made to reintroduce the species. From 2001 to 2003 four batches (a total of 32 individuals) of white rhinos were released in the Moremi Game Reserve. All were fitted with transmitters, ear notched and monitored on a regular basis. Rhinos released in the last batch moved significantly further from the release site compared to early batches. Six female rhinos from the last batch dispersed out of the Reserve. Activity area (95% minimum convex polygon; MCP) sizes decreased with years after release and increasing density of rhinos but only density had an effect on the core area (50% MCP) sizes. We conclude that the number of rhinos present in the area of release should be carefully considered before further individuals are released. When released in an area with rhinos that have established territories, the newly reintroduced individuals may be forced to disperse. If other areas of suitable habitat are available elsewhere in the same protected area, animals should be released at different sites to avoid unwanted long-term dispersal and to use the inverse density-dependent activity area sizes to maximize the rhino population in an area.