Direct Competition For Resources Research Articles

Immune activity suppresses reproduction in food‐limited female tree lizards Urosaurus ornatus

Summary When resources are scarce, organisms are faced with critical challenges trying to optimize competing functions. Reproduction and immune function are both resource intensive and important to most species. Most studies have reported a down‐regulation of immune function during reproduction. Conversely, it is unclear whether mounting an immune response can affect the reproductive process and few studies have examined competition for resources between these two processes. Here we report evidence for direct competition for resources between the reproductive and immune systems in a vertebrate model system, the tree lizard (Urosaurus ornatus). We manipulated food intake in reproductive female tree lizards, where half of the females were undergoing cutaneous wound healing and the other half were not. We then measured reproductive investment in all animals and wound healing rate in all wounded animals. We found that animals with unlimited access to food sustained both reproduction and immune function whereas animals maintained on a restricted diet were not. Specifically, when food was unlimited, females were able to invest in reproduction and heal their wounds. However, when food was limited, females forced to heal a cutaneous wound had significantly smaller follicles than their non‐wounded counterparts. Under extreme food limitation (i.e. no food) both reproductive investment and wound healing were suppressed. These results clearly demonstrate resource competition between the reproductive and immune systems, whereby physiological trade‐offs between the two systems only arise when resources are limiting. Furthermore, this type of facultative regulation is adjustable and allows animals to respond to changing environmental conditions.

A mathematical model on the effect of M. denticulata weed on different winter crops

Many weeds interfere with the productivity of wheat and other winter annual crops; however, one common weed Medicago denticulata, appears to have a beneficial effect. An experiment was conducted at Agricultural Experimental Farm of the Indian Statistical Institute, Giridih, Jharkhand to observe the effect of M. denticulata (a legume) on different crops yield of barley ( Hordeum vulgare Sensu lato), linseed ( Linum usitatissimum L.), Indian mustard [ Brassica juncea (L.) Czernj. & Cosson] and wheat ( Triticum aestivum L.). The commensalisms interaction was studied, in which one species benefits, while the other is unaffected, between the crops, M. denticulata and other weeds, to observe the role of medicago as biological control agent of other weeds for enhancement of crop productivity. Further, a statistical test was performed to establish the effect of M. denticulata and weed infestations based on one-step Markov structure of the covariance matrix of the biomass. This permitted development of a mathematical model of a crop– M. denticulata–other weeds system and their interactions through direct and indirect competition for resources. Crops yield decreased considerably due to the presence of other weeds, while it increased due to introduction of medicago and hence medicago acted as a controlling agent in a crop– M. denticulata–other weeds system. Our mathematical analysis supported the experimental findings. The model parameters are estimated through a nonlinear least square and stochastic differential equations. Moreover, some thresholds for the growth of medicago population came out from our analysis that may be used as a biological control threshold for the enhancement of crop productivity.

Apparent competition: an impact of exotic shrub invasion on tree regeneration

Invasion of habitats by exotic shrubs is often associated with a decrease in the abundance of native species, particularly trees. This is typically interpreted as evidence for direct resource competition between the invader and native species. However, this may also reflect indirect impacts of the exotic shrubs through harboring high densities of seed predators––known as apparent competition. Here I present data from separate seed predation experiments conducted with two shrub species exotic to North America; Rosa multiflora, an invader of abandoned agricultural land, and Lonicera maackii, an invader of disturbed or secondary forest habitats. Both experiments showed significantly greater risks of seed predation for tree seeds located under shrub canopies when compared to open microhabitats within the same site. These results indicate the potential importance of indirect impacts of exotic species invasions on native biota in addition to the direct impacts that are typically the focus of research.

Matrix Models as a Tool for Understanding Invasive Plant and Native Plant Interactions

Abstract: Demographic matrix models are an increasingly standard way to evaluate the effects of different impacts and management approaches on species of concern. Although invasive species are now considered among the greatest threats to biodiversity, matrix methods have been little used to explore and integrate the potentially complicated effects of invasions on native species. I developed stage‐structured models to assess the impacts of invasive grasses on population growth and persistence of a federally listed (U.S.A.) endemic plant, the Antioch Dunes evening primrose (Oenothera deltoides subsp. howellii [Munz] W. Klein). I used these models to evaluate two frequently made assumptions: (1) when rare plant populations decline in invaded habitats, invasive species are the cause and (2) invasive plants suppress rare plants primarily through direct resource competition. I compared two control and two removal matrices based on previous experimental work that showed variable effects of invasive grasses on different life‐history stages of O. deltoides. Matrix analysis showed that these effects translated into substantial changes in population growth rates and persistence, with control matrices predicting a mean stochastic population growth rate (λ) of 0.86 and removal matrices predicting growth rates from 0.92 to 0.93. Yet even the most optimistic invasive removal scenarios predicted rapid decline and a probability of extinction near one in the next 100 years. Competitive suppression of seedlings had much smaller effects on growth rates than did lowered germination, which probably resulted from thatch accumulation and reduced soil disturbance. These results indicate that although invasive grasses have important effects on the population growth of this rare plant, invasion impacts are not solely responsible for observed declines and are likely to be interacting with other factors such as habitat degradation. Further, changes in the disturbance regime may be as important a mechanism creating these impacts as direct resource competition. My results highlight the value of demographic modeling approaches in creating an integrated assessment of the threats posed by invasive species and the need for more mechanistic studies of invasive plant interactions with native plants.

The earliest Helicosalpinx from Canada and the global expansion of commensalism in Late Ordovician sarcinulid corals (Tabulata)

Spiral embedment cavities that formed around metazoan endosymbionts are preserved in the septa and intercorallite spaces of Columnopora and Calapoeciacorals from Manitoulin Island, Ontario. These are the oldest described Helicosalpinx asturiana, and this report extends the range of these trace fossils from the Richmondian (Ashgill, Upper Ordovician) to the Givetian (upper Middle Devonian). The sinistrally coiled traces show regular morphology, suggesting a physiological basis for their shape. Coral growth parameters are not affected by the presence of Helicosalpinx, suggesting that the endosymbiont was not parasitic and not in direct competition for resources with the host. H. asturiana is interpreted as trace fossil evidence of commensalism. Two additional endosymbiotic traces occur in Late Ordovician Columnopora. The particular association of straight, cylindrical Chaetosalpinx with Columnopora is widespread during the Richmondian. A dependent association is suggested to have originated between the endosymbiont and Columnopora prior to the Richmondian expansion and to have continued into the Hirnantian (latest Ordovician). The association between this endosymbiont and host is the earliest known temporally and globally significant inter-metazoan symbiosis. Although host corals, Columnopora and Calapoecia, did not survive the end-Ordovician mass extinction events, both Chaetosalpinx and Helicosalpinx occur in other host corals during the Silurian and Devonian.

Mechanisms underlying the interaction betweenPinus halepensisand the native late‐successional shrubPistacia lentiscusin a semi‐arid plantation

Pinus halepensishas been extensively planted in semi‐arid areas throughout the world. This has often led to slow‐growth stands that: a) suffer from insect plagues, b) promote nutrient depletion and c) fail to promote the recovery of native vegetation. The introduction of native late‐successional shrubs in these stands could stimulate successional processes, improve soil conditions and enhance their resilience against disturbances. The main objective of this study was to evaluate the mechanisms underlying the interaction betweenPinusand the native late‐successional shrubPistacia lentiscusin a semi‐arid plantation. By using manipulative field and laboratory experiments, we evaluated direct (competition for soil resources and allelopathic effects) and indirect (competition with herbaceous understorey) interactions betweenPinusandPistacia. We found no effect ofPinuslitter and root exudates onPistaciagrowth. In the field,Pistaciaseedlings planted under the canopy ofPinusshowed higher survival than those planted in open areas with sparse vegetation. Girdling ofPinustrees did not affect the performance of plantedPistaciaseedlings, but suppression of the herbaceous understorey significantly enhanced both survival and physiological status ofPistaciaseedlings planted under the canopy ofPinus. The magnitude of the interference by herbaceous understorey was considerably higher than that byPinus. Our results provide evidence that a negative indirect interaction betweenPinusandPistacia, mediated by the herbaceous understorey, is taking place in the afforestation studied, and can help to explain the low rates of colonisation of late‐successional woody shrubs typically observed in semi‐aridPinushalepensisplantations.

The earliest Helicosalpinx from Canada and the global expansion of commensalism in Late Ordovician sarcinulid corals (Tabulata)

Spiral embedment cavities that formed around metazoan endosymbionts are preserved in the septa and intercorallite spaces of Columnopora and Calapoeciacorals from Manitoulin Island, Ontario. These are the oldest described Helicosalpinx asturiana, and this report extends the range of these trace fossils from the Richmondian (Ashgill, Upper Ordovician) to the Givetian (upper Middle Devonian). The sinistrally coiled traces show regular morphology, suggesting a physiological basis for their shape. Coral growth parameters are not affected by the presence of Helicosalpinx, suggesting that the endosymbiont was not parasitic and not in direct competition for resources with the host. H. asturiana is interpreted as trace fossil evidence of commensalism. Two additional endosymbiotic traces occur in Late Ordovician Columnopora. The particular association of straight, cylindrical Chaetosalpinx with Columnopora is widespread during the Richmondian. A dependent association is suggested to have originated between the endosymbiont and Columnopora prior to the Richmondian expansion and to have continued into the Hirnantian (latest Ordovician). The association between this endosymbiont and host is the earliest known temporally and globally significant inter-metazoan symbiosis. Although host corals, Columnopora and Calapoecia, did not survive the end-Ordovician mass extinction events, both Chaetosalpinx and Helicosalpinx occur in other host corals during the Silurian and Devonian.

The Mesolithic-Neolithic Transition on the Channel Islands: Adopting Agriculture in an Emerging Island Landscape

An examination of how and why Channel Island society adopted agriculture is aided in this paper by an island-based approach, which stresses the social and environmental implications of island life. This paper proposes a two-stage model of neolithisation of indigenous island hunter-gathers, beginning with a phase of cooperative interaction between forager and farmer in the early stages of the transition, followed by a later phase of direct competition for island resources. A rapid shift from cooperative to competitive interaction is proposed, amplified by constraints of island biogeography, sea-level change and insularity. Islanders were 'pulled' toward a Neolithic world view through increased exchange, while environmental conditions and limitations on the islands 'pushed' indigenous island hunter-gatherers to adopt agriculture.

The Mesolithic-Neolithic Transition on the Channel Islands: Adopting Agriculture in an Emerging Island Landscape

An examination of how and why Channel Island society adopted agriculture is aided in this paper by an island-based approach, which stresses the social and environmental implications of island life. This paper proposes a two-stage model of neolithisation of indigenous island hunter-gathers, beginning with a phase of cooperative interaction between forager and farmer in the early stages of the transition, followed by a later phase of direct competition for island resources. A rapid shift from cooperative to competitive interaction is proposed, amplified by constraints of island biogeography, sea-level change and insularity. Islanders were 'pulled' toward a Neolithic world view through increased exchange, while environmental conditions and limitations on the islands 'pushed' indigenous island hunter-gatherers to adopt agriculture.

Impacts of woodland deer on small mammal ecology

Summary The possible impacts of increased deer populations on small mammal ecology in British lowland woodlands are reviewed. These impacts occur mainly through two pathways. First, by the modification or removal of habitat which influences food supply, cover and the balance of competition between the species. Secondly, through direct competition for resources, particularly food supplies. Losses of woodland ground vegetation may provoke major changes in small mammal community structure which, in the extreme, may decrease from five to eight species, or more, to just wood mice (Apodemus sylvaticus). Reduction of understorey species such as hazel (Corylus avellana) or loss of shrub diversity, would be expected to lead to declines in yellow-necked mice (Apodemus flavicollis) and common dormice (Muscardinus avellanarius). Reduction of early succession mixed scrub and grassland may reduce colonization by shrews, harvest mice (Micromys minutus) and field voles (Microtus agrestis), although in woodland rides, field voles may benefit from preferential grazing of grasses by deer. Impacts on regeneration which may delay or inhibit canopy/understorey closure may encourage the ground and shrub vegetation and so favour species with a preference for ground cover such as the bank vole (Clethrionomys glareolus). Reductions in the availability of foods (e.g. mast crops) may reduce the potential for high population densities, particularly of bank voles, wood mice and yellow-necked mice, decrease the lengths of breeding seasons, and further affect community structure. If rodent densities are lowered, avian and terrestrial predators are likely to suffer reduced breeding success and tawny owls (Strix aluco) may prey more heavily on bank voles if their favoured ground cover is reduced. Studies at Wytham Woods, near Oxford, from 1949 to 1999, indicate that a significant reduction in bank vole, but not wood mouse, numbers has occurred; this is suggested to be the result of observed changes in the woodland vegetation, including a significant reduction in the ground cover of bramble (Rubus fruticosus agg.). Deer, as well as increased canopy shading, are probably the major factors causing this change in habitat and small mammal density.

Non‐competitive phenotypic differences can have a strong effect on ideal free distributions

Abstract We present a model of the ideal free distribution (IFD) where differences between phenotypes other than those involved in direct competition for resources are considered. We show that these post‐acquisitional differences can have a dramatic impact on the predicted distributions of individuals. Specifically, we predict that, when the relative abilities of phenotypes are independent of location, there will be a continuum of mixed evolutionarily stable strategy (ESS) distributions (where all phenotypes are present in all patches). When the relative strengths of the post‐acquisitional trait in the two phenotypes differ between patches, however, we predict only a single ESS at equilibrium. Further, this distribution may be fully or partially segregated (with the distribution of at least one phenotype being spatially restricted) but it will never be mixed. Our results for post‐acquisitional traits mirror those of Parker (1982) for direct competitive traits. This comparison illustrates that it does not matter whether individual differences are expressed before or after competition for resources, they will still exert considerable influence on the distribution of the individuals concerned.

Dietary Overlap between Native Sitka Black-Tailed Deer and Introduced Elk in Southeast Alaska

We studied diet composition of native Sitka black-tailed deer (Odocoileus hemionus sitkensis) and a growing herd of introduced elk (Cervix elaphus) on Etolin Island to evaluate potential interspecific competition. Diets of deer and elk were similar during a mild, relatively snow-free winter, with both species heavily relying on salal (Gaultheria shallon), red huckleberry (Vaccinium parvifolium), and western redcedar (Thuja plicata). As expected, elk ate more grasses (Poaceae) and sedges (Cyperaceae) than deer, and deer ate more forbs and low-growing evergreen plants than elk. Relatively low plant diversity in Southeast Alaska limits options for divergence in deer and elk diets. At present, high dietary overlap probably does not infer direct competition for food resources because both deer and elk populations are relatively low, and food does not appear limiting. However, as their populations increase or should harsh winter weather reduce the variety and availability of winter foods, intra- and interspecific competition is inevitable. Crown closure following clearcut logging will decrease forage abundance and increase competition between deer and elk over the long term.

Flowering influences adventitious root formation in chrysanthemum cuttings

Root formation in chrysanthemum ( Dendranthemum grandiflora (Ramat.) Kitamura) cuttings was reduced as flowers developed on stock plants. This effect was shown for all ten cultivars evaluated in this study. Not all cultivars were affected equally by the presence of flower buds on cuttings. There was no relationship ( r 2 = 0.06) between root formation in vegetative cuttings and the ability for a cultivar to root from flowering cuttings. IBA (1 mM) could partially overcome the negative effect of flowering on root formation, but cuttings taken after the flower buds had fully opened failed to root even after auxin treatment. Removing buds from cuttings or continually removing flower buds during stock plant growth reduced rooting compared to cuttings with flower buds intact. Furthermore, cuttings taken from the top three nodes of the stock plant containing flower buds rooted comparably to cuttings taken from the lower stem section that contained only vegetative buds. The negative influence of flowering on root formation appears to be due to the photoperiodic induction of the flowering stimulus rather than a direct competition for resources between flowers and developing roots.

Within-Population Variation in Demography of Taraxacum Officinale: Season- and Size-Dependent Survival, Growth and Reproduction

1 Lefkovitch transition matrices were used to determine vital demographic rates of a natural population of Taraxacum officinale in Morgantown, WV, USA. Separate size transition matrices were calculated for each of four seasons, October-January, January-April, April-July, and July-October, to test if demographic rates vary as a function of season and if size-specific rates vary differentially among seasons. Seasondependent demography was also compared for four phenotype classes segregated by cluster analysis of leaf morphology. 2 The finite rate of increase for the entire population was largest in autumn (OctoberJanuary) and declined throughout the rest of the year. Overall, there was a small reduction in the population size. Size-specific probabilities of survival, growth and fertility varied dramatically among seasons. Sensitivity analyses showed that small individuals were particularly important to population growth from autumn to spring. Larger individuals were more important during summer. 3 Highly season-dependent demographic rates have large implications for population distribution and persistence since increased vulnerability to perturbation during particular seasons may constrain population growth and stability. Although T. officinale is a long-lived perennial, annual censuses may mask the importance of certain individuals or life history traits for maintenance of genetic variability and population viability. 4 Seasonal and annual finite rates of increase also varied as a function of phenotype class. Of two phenotype classes which had identical annual growth rates, one grew better in cool seasons while the second performed better in warm seasons. Direct competition for resources should be reduced by such inverse patterns of demography across seasons. 5 If phenotype classes are to some degree genetically determined, the differential responses observed here suggest that temporal variation in the environment could explain the maintenance of genetic diversity within populations.

Competitive regimes and female bonding in two species of squirrel monkeys (Saimiri oerstedi and S. sciureus)

Ecological and behavioral data from long-term field studies of known individuals in two closely related squirrel monkey species (Saimiri oerstedi and S. sciureus) were used to examine hypotheses about the source of variation in female bonding among group-living primates. Social relationships in species which live in cohesive groups are thought to depend on the nature of competition for resources. S. oerstedi and S. sciureus both live in large groups and are subject to intense predation. Direct feeding competition both between and within groups is extremely low in S. oerstedi; in this species female relationships are undifferentiated, no female dominance hierarchy is evident and females disperse from their natal group. S. sciureus also experiences very low levels of between-group competition, but within-group direct competition for resources is frequent; this species demonstrates differentiated female relationships, a female dominance hierarchy, and female philopatry. The correlated ecological and social variables found in these two congeners further minimize the minor effects of phylogenetic differences and emphasize the importance of food distribution in determining social characteristics.

On Limits to Seed Production

On Limits to Seed Production

Sporadic food competition with the African honey bee: projected impact on neotropical social bees

ABSTRACTBee colonies in lowland forest in Panama were monitored for pollen and nectar harvest, pollen species utilization and nectar quality and quantity per returning forager. Despite sharing most pollen resources and nectar of the same quality with 20 introduced colonies of the African honey bee (Apis mellifera), native stingless bees of 12 species were largely unaffected by its activity. Pollen and nectar harvested by the honey bees were 10–200 times that procured by 17 stingless bee colonies. This discrepancy in total harvest and general lack of competitive effect is explained by a honey bee foraging area over 10 times that of the native bees, and apparent foraging shifts to escape competition with honey bees, thus reduced potential overlap in foraging sites.Seven cases of direct resource competition for pollen or nectar were documented, out of 31 tests. Rare periods of intensive harvest were diminished by competing African honey bees. Such harvest peaks lasted for only a few hours in 13 days of observation. Despite average duration of 4% foraging time for each species, peaks included as much as 51% total harvest. Calculations based upon colony populations, food stores and flight range show that if African honey bees persist at a density of 1 colony per km2, colonies of some stingless bee species may disappear after 10 years. Their chances of escaping food competition by taxonomic specialization on flowers seem slight.

Dominance and aggression in social groups of male and female rats

Two experiments were performed to examine aggression and dominance in domestic male and female Rattus norvegicus living in small mixed-sex (3 males and 3 females) groups. Experiment 1 examined the development of aggression in females. A single female (alpha) within each of the six colonies tested showed the preponderance of attacks on male intruders placed into the home-cage when male colony residents were absent. Over 12 weeks of intruder-aggression training female alphas showed only a mild nonsignificant elevation of aggressive behavior. A comparison of aggression of male and female colony alphas tested with opponents of each sex revealed that aggression was mainly directed at like-sex opponents, and that female attack was more defensive in character than male attack regardless of opponent sex. The highest intensity of aggression occurred when male alphas confronted male intruders. Although intruders never showed offense toward male residents, 61% of intruding males showed offense in response to attack by females. Experiment 2 investigated the relationship between aggressive dominance and competitive measures of dominance within each of 10 mixed-sex colonies. Alpha stat s of male and female colony residents did not reliably predict priority of access to food or water in tests of direct resource competition with like-sex colony members. When colony males were simultaneously tested for copulation, the copulatory behavior of alpha males was significantly greater than that of other colony males. Results are discussed in relation to the role of aggression in the reproductive strategy of male and female Rattus norvegicus .

Faculty and the State Policy Process

Over the past decade, state policymaking in higher education has changed dramatically. Demographic shifts leading to declining enrollments in many states, fiscal stress forcing retrenchment, public cries for accountability, and the changing educational demands of today's students of all ages have worked together to shift policy power away from traditional academic arenas and into political ones. Decisions once made on campus by deans and academic vice-presidents are increasingly made at the statehouse by higher education agency staff and legislative budget analysts [5, p. 29]. The shift in power is compounded by the more centralized financing arrangements within state governments, which have placed education in more direct resource competition with other public sector services [6, p. 76]. Faculty collective bargaining has facilitated the centralization of personnel and salary decisions [1, p. 163]. Similarly, the expanding size and scope of statewide higher education agencies has resulted in a more centralized decision-making structure within the higher education community itself [10, p. 52]. Power, once spread among multiple actors in higher education policy, has gravitated into fewer and fewer hands. With these trends expected to accelerate in the near future, it is reasonable to assume that power in higher education will continue its shift from campus to statehouse. Apart from the obvious implications this has for institutional autonomy, it also has produced a subtle but significant change in the faculty role

Behavioral Interactions of Penned Red and Arctic Foxes

Expansion of the geographical distribution of red foxes (Vulpes vulpes) into the far north tundra region may lead to competition between arctic (Alopex lagopus) and red foxes for space and resources. Behavioral interactions between red and arctic foxes were evaluated during 9 trials conducted in a 4.05ha enclosure near Woodworth, North Dakota. Each trial consisted of introducing a male-female pair of arctic foxes into the enclosure and allowing them to acclimate for approximately a week before releasing a female red fox into the enclosure, followed by her mate a few days later. In 8 of 9 trials, red foxes were dominant over arctic foxes during encounters. Activity of the arctic foxes decreased upon addition of red foxes. Arctic foxes tried unsuccessfully to defend preferred den, resting, and feeding areas. Even though the outcome of competition between red and arctic foxes in the Arctic is uncertain, the more aggressive red fox can dominate arctic foxes in direct competition for den sites and other limited resources. J. WILDL. MANAGE. 46(4):877-884 The impact of energy development on Arctic ecosystems is not yet known, but it could affect the abundance and distribution of many species. In recent years the red fox has extended its range in Arctic regions (Marsh 1938, Skrobov 1959, Macpherson 1964). If human-induced environmental changes, such as energy development, facilitate the range extension of red foxes, direct competition with the arctic fox could intensify in some regions. Competition for limited resources will result when both species, occupying the same space, seek the same food and denning sites. Macpherson (1970) and Danilov (1958) reported that denning sites for foxes are scarce in the Arctic, and Skrobov (1959) and Ostbye et al. (1978) reported on occupation of arctic fox dens by red foxes. Man often creates artificial food sources in the Arctic which are used by both red and arctic foxes (Vincent 1958, Klein 1973, Hanson and Eberhardt 1977, Eberhardt 1977). In northern Alaska, red foxes may also take advantage of roads for dispersal into remote areas, or use buildings and other man-made objects, such as steel pipes, for denning; this may result in higher densities of red foxes in specific localities. The purpose of this study was to determine the outcome of interactions between arctic and red foxes and to develop a more accurate scenario of the consequences of competition between the 2 species. Because the chance of seeing encounters between the 2 species in the Arctic is small, this study was conducted by observing interactions of confined fox-