Proportion Of Reproductive Individuals Research Articles

Hierarchy Establishment from Nonlinear Social Interactions and Metabolic Costs: An Application to Harpegnathos saltator

Social hierarchies are ubiquitous in social groups such as human societies and social insect colonies; however, the factors that maintain these hierarchies are less clear. Motivated by the shared reproductive hierarchy of the ant species Harpegnathos saltator, we have developed simple compartmental nonlinear differential equations to explore how key life-history and metabolic rate parameters may impact and determine its colony size and the length of its shared hierarchy. Our modeling approach incorporates nonlinear social interactions and metabolic theory. The results from the proposed model, which were linked with limited data, show that: (1) the proportion of reproductive individuals decreases over colony growth; (2) an increase in mortality rates can diminish colony size but may also increase the proportion of reproductive individuals; and (3) the metabolic rates have a major impact in the colony size and structure of a shared hierarchy.

Are protected areas good for the human species? Effects of protected areas on rural depopulation in Spain

Protected areas (PAs) seek to conserve valuable genes, species and ecosystems by applying a legal regime that restricts some socioeconomic activities and also offers opportunities for new ones. As a result, PAs have been claimed by some authors to boost socioeconomic conditions in rural areas mainly through tourism activities. However, others have claimed that PAs contribute to rural depopulation through the worsening of living conditions of local residents because of restrictions resulting from protection regulations. Here, we applied a multiple-paired Before-After-Control-Impact (BACI) research design on a census on protected rural municipalities (cases; N = 52) versus unprotected rural municipalities (controls; N = 55) in Spain to ascertain whether PAs had positive or negative effects on rural populations using three indicators on depopulation with official municipal data from 1996 until 2019: Compound annual growth rate (CAGR); Proportion of reproductive individuals (REP); and Proportion of reproductive females (WREP). We controlled for some confounders such as biophysical characteristics and regional regulations by carefully selecting our sample of municipalities spatially. Our results show that depopulation figures were worse in cases than in controls, with some exceptions whose characteristics should be further explored. Municipalities in Sites of Community Importance (SCIs) performed best against rural depopulation and generally better than their controls, whereas municipalities in Biosphere Reserves and Special Protection Areas (SPAs) showed mostly worse figures. Our findings suggest that, while necessary and important for biodiversity, multiple-use PAs generally entailed negative consequences for Spanish rural populations that need to be offset by State's intervention.

The Demography of Gentiana autumnalis in Populations Under Varying Management Regimes in New Jersey

Gentiana autumnalis (pine barren gentian) is a rare, fall-flowering perennial that is endemic to pine barren habitat from New Jersey to South Carolina. This disturbance-adapted, early successional species is at risk in New Jersey as a result of human interactions, namely growing season mowing and fire suppression. We used a repeated measures design to compare the differences between managed (mowing and prescribed fire) and unmanaged G. autumnalis populations for density, life stage, mortality, and fecundity. Managed populations had a greater gentian density, proportion of reproductive individuals, and seedlings compared to unmanaged populations. Implementing prescribed burns and mowing at previously unmanaged sites prior to spring growth increased gentian density, flowering, and seed set the same year. Our data support that prescribed burning and mowing can be beneficial management tools for the conservation of G. autumnalis and other disturbance-adapted species that require open early-successional habitat. However, their implementation can have negative consequences if conducted during the growing season, especially for roadside populations that are periodically mowed. Declining rare plant populations have the potential to benefit from management practices that facilitate ideal growing conditions and influence life stage transitions that will best improve population growth rate over time.

Disentangling exploitation of the intertidal grazer Phorcus sauciatus (Gastropoda: Trochidae) in an oceanic archipelago: Implications for conservation

AbstractHarvesting of intertidal grazers such as topshells is known to affect negatively the exploited populations by altering population structure and decreasing abundance. Phorcus sauciatus has a wide geographic distribution in the North‐eastern Atlantic Ocean and is subject to increasing levels of harvesting pressure due to the expansion of human population on coastal areas. The effect of proximity to human settlements and coastal accessibility on the size structure and abundance of P. sauciatus populations was examined in Madeira archipelago. Mean size, proportion of reproductive individuals, and abundance of this species were generally smaller in areas closer to human settlements and in more accessible coastal areas. Marine protected areas returned the highest mean sizes evidencing their effectiveness in preserving the size structure of this species. The results highlight the necessity to regulate the harvest of P. sauciatus in Madeira archipelago, as well as the implementation of management measures aiming at the sustainable exploitation and conservation of this species, exploited in this region since the early 15th century.

Does a correlation exist between environmental suitability models and plant population parameters? An experimental approach to measure the influence of disturbances and environmental changes

Due to increasing human pressures, there is a need to understand how environmental and anthropogenic disturbances could affect the conservation status of endangered plant species. When information on distribution or population parameters is poor, Species Distribution Models (SDMs) may offer a valuable additional source to assess threats and to evaluate conservation options. In this sense, if the output of SDMs represents the relationships between habitat features and species occurrence, SDM results can also be related to other key parameters of population. For the endangered yellow gentian, we tested the relationship between six field population parameters and the suitabilities obtained by SDMs with natural and limiting parameters (i.e. proxies of disturbances). Specifically, the six population parameters were the surface area covered by each population, the number of vegetative and reproductive individuals per population, the density of reproductive and all individuals per plot and the proportion of reproductive individuals. Thus, threats were evaluated by testing if relationships between population parameters and suitabilities increased when proxies of disturbances were included in models.Best-fitting models resulted when all natural and human disturbance variables were included. In addition, results show relationships between suitability and population parameters only when disturbance parameters were used for SDMs. When the index related to the sensitivity to climate change was included in SDMs, the density of all individuals and number of reproductive plants were lower than in low suitability sites, suggesting that climate change is likely already challenging the ability of yellow gentian to bloom and germinate. Otherwise, we observed a decrease of the extent of localities in areas with higher suitability obtained through the index related to trail intensity. This confirmed the positive effect of conservation activities, which were mainly implemented in the proximity of trails.Using a thoroughly studied plant species as a straightforward example, we showed the potentiality of SDMs to inform on population parameters instead of only discriminate species presence or absence. This information can suggest the use of disturbance parameters when specific SDMs aim to support strategic decisions in management and conservation.

Annual age structure and reproduction in the Caatinga red-nosed mouse, Wiedomys pyrrhorhinos (Rodentia, Sigmodontinae)

Introduction: We analyzed the variation in the age structure, sex ratio, proportion of reproductive individuals, age and size at sexual maturity, and litter size in a population of the sigmodont rodent Wiedomys pyrrhorhinos. We compared the observed distributions with the monthly rainfall for the same period, to identify the reproductive period and to assess the effects of the rains on the age structure of the population during the ensuing months. We further compared our results with age structure patterns recovered from other documented rodent outbreaks to identify possible causes of a presumptive population outbreak represented by this series. Methodology: Museum samples had been obtained between July 1953 and February 1955 from 40 sites in Caruaru, Pernambuco, Brazil. Records from a total of 2280 individuals, 1834 of which represented by their skulls, were analyzed. Skulls were sorted into seven age classes based on molar eruption and wear. Monthly rainfall during the entire collecting period was analyzed for putative correlations with monthly frequencies of specimens and of indicators of reproductive condition, tabulated for each sex and age class. Results: Monthly frequency distributions of age classes presented separated and consecutive modal peaks, conforming to an age structured population. Monthly proportions of pregnant females were highly correlated with the amount of rainfall of the same and of the previous month, although records of pregnant females were obtained every month between July 1953 and December 1954. Pregnant females were found from age class 2 on. From January to April, 1954, reproductive females belonged to age classes 5 to 7. From May to September a wide range of age classes was documented among pregnant females, and from October to December only those of age classes 2 to 4 were recorded. Litter size varied throughout the year, with larger averages and ranges at midwet season (June-August) and was highly correlated with female weight, female length and with the amount of rainfall of the previous 30 days. Higher means in litter size were also in phase with higher proportions of pregnant females and with the age class 1 peak. Discussion and Conclusion: The population peak occurred four to six months after the rainfall peak (September – November) and was primarily comprised of young adults. After this period, the pregnancy rates were very low, ceasing completely by January, 1955, when most of the individuals belong to older age classes. This shift in age structure from younger to older individuals during population decline indicated that the samples documented an outbreak episode in 1954. This episode was possibly related to the unusual rainfall in November 1953, apparently sufficient to support two closely-spaced breeding seasons, with the second amplifying the effect of the first.

Hierarchical reproductive allocation and allometry within a perennial bunchgrass after 11 years of nutrient addition.

Bunchgrasses are one of the most important plant functional groups in grassland ecosystems. Reproductive allocation (RA) for a bunchgrass is a hierarchical process; however, how bunchgrasses adjust their RAs along hierarchical levels in response to nutrient addition has never been addressed. Here, utilizing an 11-year nutrient addition experiment, we examined the patterns and variations in RA of Agropyron cristatum at the individual, tiller and spike levels. We evaluated the reproductive allometric relationship at each level by type II regression analysis to determine size-dependent and size-independent effects on plant RA variations. Our results indicate that the proportion of reproductive individuals in A. cristatum increased significantly after 11 years of nutrient addition. Adjustments in RA in A. cristatum were mainly occurred at the individual and tiller levels but not at the spike level. A size-dependent effect was a dominant mechanism underlying the changes in plant RA at both individual and tiller levels. Likewise, the distribution of plant size was markedly changed with large individuals increasing after nutrient addition. Tiller-level RA may be a limiting factor for the adjustment of RA in A. cristatum. To the best of our knowledge, this study is the first to examine plant responses in terms of reproductive allocation and allometry to nutrient enrichment within a bunchgrass population from a hierarchical view. Our findings have important implications for understanding the mechanisms underlying bunchgrass responses in RA to future eutrophication due to human activities. In addition, we developed a hierarchical analysis method for disentangling the mechanisms that lead to variation in RA for perennial bunchgrasses.

Effects of harvesting intensity on population structure of Lippia graveolens (Verbenaceae, Lamiales) in the Semidesert of Queretaro, Mexico

Whole Oregano (Lippia graveolens) is a wild shrub species that is harvested commercially as an important complement to the income of farmers in the semiarid areas of Mexico. However, the impact of this activity on populations of the species is unknown, particularly in the semi-desert of Queretaro State in Mexico. We quantified the consequences of different harvest rates on the growth and reproduction of five wild populations of L. graveolens, with the goal of improving current practices. We found that, as the harvesting rates of L. graveolens increase, there are changes in the density, size structure, proportion of reproductive individuals and production of inflorescences. For instance, in sites with the lowest harvesting intensity, the density was 2980 individuals/ha, the mean plant height was 100 ± 3.25 cm (mean ± SE) and mean plant cover was 4312 ± 247 cm2; whereas in sites with the highest plant harvesting intensity the density was 1920 individuals/ha, mean plan height was 30 ± 1.93 cm and mean plant cover was 843 ± 73 cm2. Such changes place certain managed wild oregano populations in a vulnerable situation, illustrating the need of close monitoring of species harvested from the wild as cash crops. Key words: Extraction, spices, population dynamics, non-wood forest products.

Estructura poblacional de Teline monspessulana (L.) K. Koch en fragmentos de bosque maulino en Chile central

In this note we examine the population structure of Teline monspessulana, an exotic plant that is invading fragments of the Maulino Forest. We evaluate density T. monspessulana, sizes, proportion of reproductive individuals and his relation with the size of the patches in 8 forest fragments. Our results indicate a high proportion of individuals growing inside fragments. Moreover, the fragment size is not correlated with T. monspessulana density.

Estructura poblacional de Pinus radiata D.Don en fragmentos de Bosque Maulino en Chile central

In this note we examine the population structure of Pinus radiata, exotic plant that is invading fragments of the Maulino Forest. We evaluate pine density, age, proportion of reproductive individuals across 8 forest fragments. Our results indicate a high proportion of young individuals and reproductive individuals growing inside fragments. Moreover, the fragment size is negatively correlated with pine density but, the proportion of reproductive individuals are not correlated with this landscape attribute. Our result indicate the existence of a pine population that is actively invading forest fragments, a fact that needs to be considered in conservation plans of this native forest.

Living on the edge: roads and edge effects on small mammal populations

1. Roads may affect wildlife populations through habitat loss and disturbances, as they create an abrupt linear edge, increasing the proportion of edge exposed to a different habitat. Three types of edge effects have been recognized: abiotic, direct biotic, and indirect biotic. 2. We explored the direct biotic edge effects of 3- to 4-m wide roads, and also a previously unrecognized type of edge effect: social. We live-trapped two threatened endemic rodents from Cozumel Island (Oryzomys couesi cozumelae and Reithrodontomys spectabilis) in 16 plots delimited by roads on two sides, to compare edge effects between two adjacent edges (corners), single-edge and interior forest, on life history and social variables. 3. No significant edge effects were observed on the life-history variables, with the exception of differences in body condition between males and females of O. c. cozumelae near edges. Both species showed significant and contrasting effects on their social variables. 4. O. c. cozumelae was distributed according to its age and sex: the proportion of adults and males was higher in interior than near edges, while juveniles and females were more abundant near edges. More nonreproductive females were present in corners than in single-edge and interior, while the opposite distribution was observed for nonreproductive males. 5. The distribution of R. spectabilis was related to its age and reproductive condition, but not to its sex. The proportion of adults was significantly higher in corners, while juveniles were only caught in single-edge and interior quadrants. The proportion of reproductive individuals was higher in edge than interior quadrants, while reproductive females were only present in edge quadrants. 6. We found significant differences between the quadrants with the greatest edge exposure in comparison with other quadrants. The social edge effects we identified complement the typology of edge effects recognized in ecological literature. Our study provides insight into the effects that sharp road edges have on biological and social characteristics of small mammal populations, highlighting how such effects vary among species. Our findings have important conservation implications for these threatened species, but are also applicable in a broader context wherever there are abrupt edges caused by linear landscape features.