621 research outputs found
Density dependence and the spread of invasive big-headed ants (Pheidole megacephala) in an East African savanna
No full textSupercolonial ants are among the largest cooperative units in nature, attaining extremely high densities. How these densities feed back into their population growth rates and how abundance and extrinsic factors interact to affect their population dynamics remain open questions. We studied how local worker abundance and extrinsic factors (rain, tree density) affect population growth rate and spread in the invasive big-headed ant, which is disrupting a keystone mutualism between acacia trees and native ants in parts of East Africa. We measured temporal changes in big-headed ant (BHA) abundance and rates of spread over 20 months along eight transects, extending from areas behind the front with high BHA abundances to areas at the invasion front with low BHA abundances. We used models that account for negative density dependence and incorporated extrinsic factors to determine what variables best explain variation in local population growth rates. Population growth rates declined with abundance, however, the strength of density dependence decreased with abundance. We suggest that weaker density dependence at higher ant abundances may be due to the beneficial effect of cooperative behavior that partially counteracts resource limitation. Rainfall and tree density had minor effects on ant population dynamics. BHA spread near 50 m/year, more than previous studies reported and comparable to rates of spread of other supercolonial ants. Although we did not detect declines in abundance in areas invaded a long time ago (> 10 years), continued monitoring of abundance at invaded sites may help to better understand the widespread collapse of many invasive ants.Fil: Pietrek, Alejandro Gerardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina. University of Florida; Estados Unidos. Mpala Research Centre; KeniaFil: Goheen, Jacob R.. Mpala Research Centre; Kenia. University of Wyoming; Estados UnidosFil: Riginos, Corinna. Mpala Research Centre; Kenia. University of Wyoming; Estados Unidos. Nature Conservancy; Estados UnidosFil: Maiyo, Nelly J.. Ol Pejeta Conservancy; KeniaFil: Palmer, Todd M.. Mpala Research Centre; Kenia. University of Florida; Estados Unido
facilitates a competitively subordinate plant ant in Kenya
No full textBiological invasions can lead to the reassembly of communities and understanding and predicting the impacts of exotic species on community structure and functioning are a key challenge in ecology. We investigated the impact of a predatory species of invasive ant, Pheidole megacephala, on the structure and function of a foundational mutualism between Acacia drepanolobium and its associated acacia-ant community in an East African savanna. Invasion by P. megacephala was associated with the extirpation of three extrafloral nectar-dependent Crematogaster acacia ant species and strong increases in the abundance of a competitively subordinate and locally rare acacia ant species, Tetraponera penzigi, which does not depend on host plant nectar. Using a combination of long-term monitoring of invasion dynamics, observations and experiments, we demonstrate that P. megacephala directly and indirectly facilitates T. penzigi by reducing the abundance of T. penzigi’s competitors (Crematogaster spp.), imposing recruitment limitation on these competitors, and generating a landscape of low-reward host plants that favor colonization and establishment by the strongly dispersing T. penzigi. Seasonal variation in use of host plants by P. megacephala may further increase the persistence of T. penzigi colonies in invaded habitat. The persistence of the T. penzigi–A. drepanolobium symbiosis in invaded areas afforded host plants some protection against herbivory by elephants (Loxodonta africana), a key browser that reduces tree cover. However, elephant damage on T. penzigi-occupied trees was higher in invaded than in uninvaded areas, likely owing to reduced T. penzigi colony size in invaded habitats. Our results reveal the mechanisms underlying the disruption of this mutualism and suggest that P. megacephala invasion may drive long-term declines in tree cover, despite the partial persistence of the ant–acacia symbiosis in invaded areas.Fil: Palmer, Todd M.. Mpala Research Centre; Kenia. University of Florida; Estados UnidosFil: Riginos, Corinna. The Nature Conservancy; Estados Unidos. University of Wyoming; Estados UnidosFil: Milligan, Patrick D.. University of Florida; Estados Unidos. Mpala Research Centre; KeniaFil: Hays, Brandon R.. Mpala Research Centre; Kenia. University of Wyoming; Estados UnidosFil: Pietrek, Alejandro Gerardo. Mpala Research Centre; Kenia. University of Florida; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Maiyo, Nelly J.. Ol Pejeta Conservancy; KeniaFil: Mutisya, Samuel. Ol Pejeta Conservancy; KeniaFil: Gituku, Benard. Ol Pejeta Conservancy; KeniaFil: Musila, Simon. National Museums of Kenya; KeniaFil: Carpenter, Scott. University of Yale; Estados UnidosFil: Goheen, Jacob R.. Mpala Research Centre; Kenia. University of Wyoming; Estados Unido
THE PRAIRIE NATURALIST Volume 34, No. 3/4 September/December 2002
No full textSEASONAL FOOD HABITS OF COYOTES IN NORTHEASTERN KANSAS ▪ J. F. Kamler, P. S. Gipson, and C. C. Perchellet
SELECTION OF NESTING HABITAT BY SHARP-TAILED GROUSE IN THE NEBRASKA SANDHILLS ▪ B. L. Prose, B. S. Cade, and D. Hein
PATTERNS OF REPRODUCTION FOR WESTERN HARVEST MICE IN NORTH-CENTRAL KANSAS ▪ J. R. Goheen, G. A. Kaufman, and D. W. Kaufman
THE IMPACT OF RECREATIONAL TRAILS AND GRAZING ON SMALL MAMMALS IN THE COLORADO PIEDMONT ▪ C. A. Meaney, A. K. Ruggles, N. W. Clippinger, and B. C. Lubow
CHRISTMAS BIRD COUNTS FOR NORTH DAKOTA 2001 ▪ R. N. Randall 137
SARCOPTIC MANGE ON COYOTES IN NORTHEASTERN KANSAS ▪ J. F. Kamler and P. S. Gipson
WOODCHUCK RECORDED IN SALINE AND RUSSELL COUNTIES, KANSAS ▪ G. A. Kaufman and D. W. Kaufman
OBSERVATION OF ROCK WRENS USING WHITE-TAILED PRAIRIE DOG BURROWS ▪ E. R. Price 149
Erratum
Reviewers 2002
Author Index - Volume 34
Subject Index - Volume 3
Defensive Plant-Ants Stabilize Megaherbivore-Driven Landscape Change in an African Savanna
No full textSummaryTree cover in savanna ecosystems is usually regarded as unstable, varying with rainfall, fire, and herbivory [1–4]. In sub-Saharan Africa, elephants (Loxodonta africana) suppress tree cover, thereby maintaining landscape heterogeneity by promoting tree-grass coexistence. In the absence of elephants, tree encroachment may convert savannas into closed-canopy woodlands [5, 6]; when elephants increase in abundance, intensified browsing pressure can transform savannas into open grasslands [5–8]. We show that symbiotic ants stabilize tree cover across landscapes in Kenya by protecting a dominant tree from elephants. In feeding trials, elephants avoided plants with ants and did not distinguish between a myrmecophyte (the whistling-thorn tree [Acacia drepanolobium]) from which ants had been removed and a highly palatable, nonmyrmecophytic congener. In field experiments, elephants inflicted severe damage on whistling-thorn trees from which ants had been removed. Across two properties on which elephants increased between 2003 and 2008, cover of whistling-thorn did not change significantly inside versus outside large-scale elephant exclusion fences; over the same period of time, cover of nonmyrmecophytes differed profoundly inside versus outside exclusion fences. These results highlight the powerful role that symbioses and plant defense play in driving tree growth and survival in savannas, ecosystems of global economic and ecological importance.PaperFlic
RESOURCE SELECTION AND PREDATION OF NORTH AMERICAN RED SQUIRRELS IN DECIDUOUS FOREST FRAGMENTS
No full textThe North American red squirrel (Tamiasciurus hudsonicus) typically is regarded as having strong affinities for coniferous forests throughout its geographic range. In the state of Indiana, the red squirrel has expanded its geographic range concurrent with fragmentation of deciduous forests and widespread plantings of conifers. We undertook a radiotelemetry study to assess resource selection and survival of this species in 2 woodlots dominated by deciduous trees in west-central Indiana. Squirrels selected habitats with a high proportion of black walnut (Juglans nigra), avoided other hard mast-producing species, and avoided conifers. Squirrels exhibited overlapping home ranges, consistent with other studies on eastern populations. Individuals whose core areas contained conifers experienced higher survival rates than those individuals whose core areas did not contain conifers. We conclude that the increased safety conferred by conifers, as well as the presence of black walnut in these forests, are likely to contribute strongly to this species' persistence in Indiana
Human dimensions of wildlife conservation in Iran: Assessment of human-wildlife conflict in restoring a wide-ranging endangered species
No full textHuman-wildlife conflicts restrict conservation efforts, especially for wide-ranging animals whose home ranges overlap with human activities. We conducted a study to understand conflicts with, and factors influencing the perceived value of an expanding population of onagers (Equus hemionus onager) in local communities in southern Iran. We asked about locals’ perceptions of six potential management strategies intended to lessen human-onager conflict. We found that human-onager conflict was restricted to 45% of respondents within the Bahram-e-Goor Protected Area, all of whom were involved in farming or herding activities. Locals within the protected area were more knowledgeable about onagers and valued onagers more than those living outside the protected area. The perceived value of onagers increased with level of education, total annual income, and perceptions of onager population trends; the perceived value of onagers decreased with the magnitude of conflict between onagers and locals. To tolerate or avoid conflicts with onagers, locals were supportive of monetary compensation and changing from a traditional lifestyle to industrialized farming (for farmers) or livestock production (for herders) with the help of government; locals did not support selling land to the government. Our study is among the first in human-wildlife conflict and local attitudes towards an endangered species and its recovery in Iran. We conclude that current levels of human-onager conflict are relatively low and perceived value of onagers is still relatively high. Therefore, wildlife authorities should consider the development of mitigation strategies with local communities before conflicts intensify.</div
Species–energy theory, pulsed resources, and regulation of avian richness during a mountain pine beetle outbreak
No full textParameter estimates of factors influencing perceived value of onagers resulted from a beta regression model (pseudo R<sup>2</sup> = 0.21, z = 10.96, p<0.001) for locals within and outside the Bahram-e-Goor Protected Area, Iran.
No full textPositive estimates indicate positive association between a factor and perceived value of onagers.</p
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Climatic variation modulates the indirect effects of large herbivores on small‐mammal habitat use
No full text1. Large mammalian herbivores (LMH) strongly shape the composition and architecture of plant communities. A growing literature shows that negative direct effects of LMH on vegetation frequently propagate to suppress the abundance of smaller consumers. Indirect effects of LMH on the behaviour of these consumers, however, have received comparatively little attention despite their potential ecological significance. 2. We sought to understand (i) how LMH indirectly shape small-mammal habitat use by altering the density and distribution of understorey plants; (ii) how these effects vary with climatic context (here, seasonality in rainfall); and (iii) the extent to which behavioural responses of small mammals are contingent upon small-mammal density. 3. We tested the effects of a diverse LMH community on small-mammal habitat use using 4 years of spatially explicit small-mammal trapping and vegetation data from the UHURU Experiment, a replicated set of LMH exclosures in semi-arid Kenyan savanna. 4. Small-mammal habitat use was positively associated with tree density and negatively associated with bare (unvegetated) patches in all plots and seasons. In the presence of LMH, and especially during the dry season, small mammals consistently selected tree cover and avoided bare patches. In contrast, when LMH were excluded, small mammals were weakly associated with tree cover and did not avoid bare patches as strongly. These behavioural responses of small mammals were largely unaffected by changes in small-mammal density associated with LMH exclusion. 5. Our results show that LMH indirectly affect small-mammal behaviour, and that these effects are influenced by climate and can arise via density-independent mechanisms. This raises the possibility that anthropogenic LMH declines might interact with changing patterns of rainfall to alter small-mammal distribution and behaviour, independent of numerical responses by small mammals to these perturbations. For example, increased rainfall in East Africa (as predicted in many recent climate-model simulations) may relax constraints on small-mammal distribution where LMH are rare or absent, whereas increased aridity and/or drought frequency may tighten them
Data from: State-dependent behavior alters endocrine-energy relationship: implications for conservation and management
No full textGlucocorticoids (GC) and triiodothyronine (T3) are two endocrine markers commonly used to quantify resource limitation, yet the relationships between these markers and the energetic state of animals has been studied primarily in small-bodied species in captivity. Free-ranging animals, however, adjust energy intake in accordance with their energy reserves, a behavior known as state-dependent foraging. Further, links between life-history strategies and metabolic allometries cause energy intake and energy reserves to be more strongly coupled in small animals relative to large animals. Because GC and T3 may reflect energy intake or energy reserves, state-dependent foraging and body size may cause endocrine-energy relationships to vary among taxa and environments. To extend the utility of endocrine markers to large-bodied, free-ranging animals, we evaluated how state-dependent foraging, energy reserves, and energy intake influenced fecal GC and fecal T3 concentrations in free-ranging moose (Alces alces). Compared with individuals possessing abundant energy reserves, individuals with few energy reserves had higher energy intake and high fecal T3 concentrations, thereby supporting state-dependent foraging. Although fecal GC did not vary strongly with energy reserves, individuals with higher fecal GC tended to have fewer energy reserves and substantially greater energy intake than those with low fecal GC. Consequently, individuals with greater energy intake had both high fecal T3 and high fecal GC concentrations, a pattern inconsistent with previous documentation from captive animal studies. We posit that a positive relationship between GC and T3 may be expected in animals exhibiting state-dependent foraging if GC is associated with increased foraging and energy intake. Thus, we recommend that additional investigations of GC- and T3-energy relationships be conducted in free-ranging animals across a diversity of body size and life-history strategies before these endocrine markers are applied broadly to wildlife conservation and management
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