Home About us Contact
|
Home About us Contact | ||
|
|
||
Territory Size (territory + size)
Selected AbstractsEffects of acidification on the breeding ecology of a stream-dependent songbird, the Louisiana waterthrush (Seiurus motacilla)FRESHWATER BIOLOGY, Issue 11 2008ROBERT S. MULVIHILL Summary 1.,We compared breeding ecology of the Louisiana waterthrush (Seiurus motacilla) on acidified and circumneutral streams in the Appalachian Highlands of Southwestern Pennsylvania from 1996 to 2005. 2.,Headwater streams impacted by acid mine drainage and/or acidic precipitation showed reduced pH (range 4.5,5.5) compared to four circumneutral streams (pH c. 7). Acid-sensitive taxa, including most mayflies (Ephemeroptera), were almost completely absent from acidified streams, whereas several acid-tolerant taxa, especially stonefly (Plecoptera) genera Leuctra and Amphinemura, were abundant. 3.,Louisiana waterthrush breeding density (c. 1 territory km,1) was significantly reduced on acidified streams compared to circumneutral streams (>2 territories km,1). Territories on acidified streams were almost twice as long as on circumneutral streams. Territories usually were contiguous on circumneutral streams, but they were often disjunct on acidified streams. Breeding density declined on one acidified stream that we studied over a 10-year period. 4.,Clutch initiation was significantly delayed on acidified streams, on average by 9 days in comparison to circumneutral streams, and first-egg dates were inversely related to breeding density. Birds nesting along acidified streams laid smaller clutches, and nestlings had shorter age-adjusted wing lengths. Stream acidity had no effect on nest success or annual fecundity (fledglings/female). However, the number of young fledged km,1 was nearly twice as high on circumneutral streams as on acidified streams. 5.,Acidified streams were characterized by a younger, less site-faithful breeding population. Individuals were less likely to return multiple years to breed, allowing inexperienced breeders to settle on acidified streams. Pairing success was lower on acidified streams, and we observed four cases of waterthrushes emigrating from territories on acidified streams to nearby circumneutral streams in the following year. 6.,We conclude that acidified headwaters constitute lower quality habitat for breeding Louisiana waterthrush. However, breeding birds can apparently compensate for reduced prey resources to fledge young on acidified streams by increasing territory size, foraging in peripheral non-acidified areas, and by provisioning young with novel prey. [source] Density effects on life-history traits in a wild population of the great tit Parus major: analyses of long-term data with GIS techniquesJOURNAL OF ANIMAL ECOLOGY, Issue 2 2006TEDDY A. WILKIN Summary 1Population density often has strong effects on the population dynamics and reproductive processes of territorial animals. However, most estimates of density-dependent effects use the number of breeding pairs per unit area in a given season and look for correlations across seasons, a technique that assigns the same density score to each breeding pair, irrespective of local spatial variation. 2In this study, we employed GIS techniques to estimate individual breeding densities for great tits breeding in Wytham Woods UK, between 1965 and 1996. We then used linear mixed modelling to analyse the effect of density on reproductive processes. 3The areas of Thiessen polygons formed around occupied nestboxes were used to approximate territory size (necessarily inverse of breeding density). There were significant, independent and positive relationships between clutch size, fledging mass and the number of offspring recruited to the population, and territory size (all P < 0·001), but no effect of territory size on lay-date or egg mass. 4Thiessen polygons are contiguous and cover all of the available area. Therefore, at low nest densities territory polygons were excessively oversized. Using a novel procedure to address this limitation, territory sizes were systematically capped through a range of maxima, with the greatest effect in the models when territories were capped at 0·9,2·3 ha. This figure approximates to the maximum effective territory size in our population and is in close agreement with several field-based studies. This capping refinement also revealed a significant negative relationship between lay-date and territory size capped at 0·9 ha (P < 0·001). 5These density-dependent effects were also detected when analyses were restricted to changes within individual females, suggesting that density effects do not merely result from either increased proportions of low-quality individuals, or increased occupation of poor sites, when population density is high. 6Overall, these results suggest that, in the current population, great tits with territories smaller than c. 2 ha independently lay smaller and later clutches, have lighter fledglings, and recruit fewer offspring to the breeding population. These analyses thus suggest a pervasive and causal role of local population density in explaining individual reproductive processes. [source] Spatial organization, group living and ecological correlates in low-density populations of Eurasian badgers, Meles melesJOURNAL OF ANIMAL ECOLOGY, Issue 3 2002Eloy Revilla Summary 1,Territoriality and group living are described in a low-density population of Eurasian badgers, Meles meles L., by studying the patterns of spatial grouping and territory marking, as well as the differences between individuals in some of their characteristics (body condition and dispersal) and in their space use (seasonally, periods of activity and interaction between pairs of individuals) under strong seasonal fluctuations in the availability of the key resource (young rabbits, Oryctolagus cuniculus L.). Finally, the role of the spatial distribution of the main prey (young rabbits) in the development of sociality was also studied in order to test some of the assumptions and predictions of the resource dispersion hypothesis (RDH). 2,Badgers were territorial, showing a flexible system of territory marking, which includes the marking of the most used areas (sett-latrines at the centres of activity) and additionally, at the smaller territories, a system of border-latrines in the areas of contact between territories. The maximum use of border-latrines was associated with the reproductive season, and that of sett-latrines with the season of food scarcity. 3,In the study area where badgers had rabbits as main prey, territories were occupied by small groups of animals, formed by one adult female who reproduced, one adult male who also showed signs of reproductive activity, the cubs of the year (if there was reproduction) and some animals born during previous years, which remained in their natal territory until their dispersal (normally during the mating season of their third or fourth year of life). This system was not strictly fixed as males, given the opportunity, expanded their territories to encompass additional females. Territories in another study site were occupied by one adult female (marked), plus the cubs of the year and another adult individual (unmarked). 4,In winter and spring dominant females and subordinates used only a small fraction of their territories, moved short distances, at a low speed and covering small areas per night. These seasons corresponded with the reproduction of rabbits (highest food availability). Dominant females were the only individuals using all the territory available in the summer (lowest food availability), when badgers had the worst body condition. Food availability increased again in autumn, as did body condition, while range sizes were again reduced. Dominant males used the same proportion of their territories over all seasons. However, in winter (reproductive season) they moved faster, over longer distances, and covered larger areas per period of activity. These results indicate that use of space by dominant males was affected by different factors from that of dominant females and subordinates. 5,RDH does not seem to explain group living in our populations because: (a) territoriality in each pair of primary animals was driven by different factors (trophic resources for females and females for males); (b) dominant males acted as expansionists; and (c) territory size was related to its richness and not to patch dispersion. 6,We propose an integrative hypothesis to explain not only group formation but also interpopulation variability in the social organization of badgers within ecological, demographic and behavioural constraints and in the light of current theory on delayed dispersal. [source] Mechanisms of population regulation in the fire ant Solenopsis invicta: an experimental studyJOURNAL OF ANIMAL ECOLOGY, Issue 3 2001Eldridge S. Adams Summary 1We tested for density-dependent regulation of biomass in a population of the fire ant Solenopsis invicta and examined the mechanisms of population recovery following replicated colony removals. 2,All colonies were killed within the core area (1018 m2) of six plots, while six additional plots served as undisturbed controls. Over the next 5 years, colonies were mapped several times per year and the biomass of each colony was estimated from the volume of the nest-mound. 3,The average biomass and density of colonies within the removal areas gradually converged on those of control plots and were no longer detectably different after two years. Thereafter, ant biomass on experimental and control plots showed nearly identical seasonal and yearly fluctuations. 4Territories of colonies surrounding the removal areas rapidly expanded following the deaths of neighbours, while average territory size on control plots showed little short-term change. 5,Significantly more new colonies were established within core areas of experimental plots than within core areas of control plots during the first year following removals. 6,The per-colony probability of movement and the net influx of colony biomass were significantly higher in central regions of the experimental plots than in control plots during the first year. The directions of colony movements were clustered towards the centres of experimental plots in the first 2 years, but did not show significant directional trends on control plots. 7,In all 5 years of the study, annual mortality rates were lower for larger colonies, but the size-specific risk of mortality was not significantly affected by the experimental removal of competitors. 8,The growth rates of colonies, adjusted for initial size, were significantly higher in central regions of experimental plots than in control plots during the first two years of the study. In all years, colony growth rates declined with increasing colony size. 9,These results indicate that populations of S. invicta are regulated by competition among neighbouring colonies. Due to large intraspecific variation in colony size, the dynamics of ant populations are described more accurately by measures of total ant biomass than by colony density alone. [source] Population density affects foraging behavior of male Black-throated Blue Warblers during the breeding seasonJOURNAL OF FIELD ORNITHOLOGY, Issue 2 2007Robert C. Dobbs ABSTRACT Foraging behavior often reflects food availability, a resource that may increasingly limit breeding birds as intraspecific crowding increases. Measuring foraging behavior, therefore, provides a way to investigate effects of population density on food limitation, an important link in understanding how crowding functions to regulate populations. We quantified three components of foraging behavior (prey attack rate, foraging speed, and relative use of morphologically constrained attack maneuvers) for male Black-throated Blue Warblers (Dendroica caerulescens) breeding under experimentally manipulated density conditions. Building on the previous work showing the density of conspecific neighbors affects territory size, reproductive success, and the time budgets of males (Sillett et al. 2004, Ecology 85: 2467,2477), we further show that density affects male foraging strategies. Although not differing in attack rate or foraging speed, male Black-throated Blue Warblers on territories with reduced neighbor densities used energetically expensive aerial attack maneuvers significantly less frequently than males in control (high-density) territories during both the incubation period and when provisioning nestlings and fledglings. We conclude that males altered their foraging behavior to compensate for density-related reductions in time available for foraging and that population density may constrain the time available for foraging. SINOPSIS La conducta de forrajeo muchas veces refleja la disponibilidad de alimentos, un recurso que puede limitar la capacidad reproductiva con el aumento en el número de individuos. El medir la conducta de forrajeo, puede proveer de una forma de investigar el efecto de la limitación de alimentos en la dencidad poblacional, enlace importante para entender como el acinamiento funciona para regular una población. Cuantificamos tres componentes de la conducta de forrajeo (tasa de ataque de la presa, velocidad de forrajeo, y uso relativo de maniobras de ataque con respecto a restricciones morfológicas) para machos de Dendroica caerulescens reproduciéndose bajo densidades manipuladas experimentalmente. Utilizando como base trabajos que señalan que la densidad conespecífica vecinal afecta el tamaño del territorio, el éxito reproductivo y el presupuesto utilizado por los machos (Sillett et al. 2004, Ecology 85:2467-2477) demostramos que la densidad afecta además la estrategia de forrajeo de los machos. Aunque no hay diferencia en la tasa de ataque o velocidad de forrajeo, machos en territorios con pocos vecinos, utilizaron maniobras de forrajeo energéticamente más costosas y con una frecuencia significativamente menos costosa que el grupo control (áreas con alta densidad), tanto durante la fase de incubación como la de crianza de pichones. Concluimos que los machos alteran su conducta de forrajeo para compensar por la reducción en la densidad de individuos y en el tiempo disponible para forrajear, y que la densidad de la población puede limitar el tiempo disponible para forrajear. [source] Relationship of habitat stability and intra-specific population dynamics of an obligate corallivore butterflyfishAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2005Michael P. Crosby Abstract 1.Intra-specific behavioural manifestations, as measured by territory size and conspecific agonistic encounters, population size and recruitment of the obligate corallivore butterflyfish Chaetodon multicinctus (Family: Chaetodontidae) were examined over a 5-year period at three Hawaiian coral reef sites, each receiving different levels of non-point-source terrigenous sediment runoff. 2.All three sites indicated significant correlations for percentage coral cover with territory size, fish size, and number of adult C. multicinctus, and for agonistic encounters with number of juvenile C. multicinctus. However, the site most impacted by sediment runoff indicated no significant correlations for percentage coral cover with territory size, fish length, number of adult C. multicinctus, number of agonistic encounters, or C. multicinctus juveniles; nor for number of agonistic encounters with number of juveniles. 3.The site moderately to minimally impacted by sediment runoff exhibited significant correlations for percentage coral cover with number of adults, while the site with no sedimentation impacts exhibited significant correlations for percentage coral cover with fish size, number of adults and number of juveniles. 4.Significant differences were found to exist between all three sites for agonistic encounters, territory size, fish size, number of C. multicinctus juveniles and percentage coral cover. The most highly impacted site exhibited a significantly higher number of adult C. multicinctus that were significantly smaller in size than either the minimally impacted and non-impacted sites. 5.The study design purposely selected high coral cover habitats (means ranged from 81.4% to 96.5%) at each site. Within this limited range of relatively high coral cover habitat, relative habitat stability resulting from a range of historic sediment inputs between sites appears to be the stronger forcing function for observed intra-specific behavioural manifestations, population size and recruitment than percentage coral cover. 6.Study results indicate that obligate corallivore butterflyfish behavioural manifestations, population size and recruitment may be used as a benchmark for changes in habitat stability for coral reef communities, and support the general premise of the butterflyfish indicator species hypothesis. Copyright © 2005 John Wiley & Sons, Ltd. [source] Density effects on life-history traits in a wild population of the great tit Parus major: analyses of long-term data with GIS techniquesJOURNAL OF ANIMAL ECOLOGY, Issue 2 2006TEDDY A. WILKIN Summary 1Population density often has strong effects on the population dynamics and reproductive processes of territorial animals. However, most estimates of density-dependent effects use the number of breeding pairs per unit area in a given season and look for correlations across seasons, a technique that assigns the same density score to each breeding pair, irrespective of local spatial variation. 2In this study, we employed GIS techniques to estimate individual breeding densities for great tits breeding in Wytham Woods UK, between 1965 and 1996. We then used linear mixed modelling to analyse the effect of density on reproductive processes. 3The areas of Thiessen polygons formed around occupied nestboxes were used to approximate territory size (necessarily inverse of breeding density). There were significant, independent and positive relationships between clutch size, fledging mass and the number of offspring recruited to the population, and territory size (all P < 0·001), but no effect of territory size on lay-date or egg mass. 4Thiessen polygons are contiguous and cover all of the available area. Therefore, at low nest densities territory polygons were excessively oversized. Using a novel procedure to address this limitation, territory sizes were systematically capped through a range of maxima, with the greatest effect in the models when territories were capped at 0·9,2·3 ha. This figure approximates to the maximum effective territory size in our population and is in close agreement with several field-based studies. This capping refinement also revealed a significant negative relationship between lay-date and territory size capped at 0·9 ha (P < 0·001). 5These density-dependent effects were also detected when analyses were restricted to changes within individual females, suggesting that density effects do not merely result from either increased proportions of low-quality individuals, or increased occupation of poor sites, when population density is high. 6Overall, these results suggest that, in the current population, great tits with territories smaller than c. 2 ha independently lay smaller and later clutches, have lighter fledglings, and recruit fewer offspring to the breeding population. These analyses thus suggest a pervasive and causal role of local population density in explaining individual reproductive processes. [source] | ||||||||||