Competitive Interactions in Ant Assemblage in a Rocky Field Environment: Is Being Fast and Attacking the Best Strategy?

The ant assemblage structure can be molded by mechanisms such as competition and dominance-discovery trade-off. In harsh circumstances is likely that ant species who control the food resource are the first to arrive at the baits, are more aggressive (behavioral dominance), abundant (numerical dominance) and, thus, ecologically dominants. By this characteristics combination, the dominance-discovery should not be a trade-off, but a positive relationship. Here, we examined the interactions among nine ant species in a rocky field area, in the Ibitipoca State Park, Minas Gerais, Brazil. By offering baits, we observe the dominance-discovery ability and the behaviors of attack, avoidance and coexistence of each species. We showed that Crematogaster sericea, Pheidole obscurithorax and Pheidole radoszkowskii were the best discoverers of the food resource and dominated it numerically, being this way considered ecologically dominants. Despite P. radoszkowskii being part of this relationship, this interpretation should be taken cautiously. Its dominance at the baits was assured by their high discovery ability and abundance, but the behavioral strategy exhibited was avoidance, not aggressiveness as C. sericea and P. obscurithorax. Thus, we can suppose that the discovery-dominance trade-off was broken by the linked characteristics that define the ecological dominant status of these species. Also, P. radoszkowskii demonstrates that others strategies could surpass the set of being fast and attack, and thus this is not the best strategy for all. In harsh circumstances each species has its own best strategy

Fast Food Delivery: Is There a Way for Foraging Success in Leaf-Cutting Ants?

Walking long distances through a trail system is an intrinsic feature of the leaf-cutting ants. Workers travel hundred of meters to forage by using well-defined physical routes which are cleared of vegetation or obstacles. Despite the costs of construction and maintenance, cleared trails should promote more benefits than non-physical ones, especially related to the leaf supply for the colony. Here, the leaf delivery rate in constructed and non-constructed trails was compared by counting the foraging flow and travel time of workers. Also the length and width of trails were measured. It was found that leaf delivery rate was 67.47% higher for foragers who were walking along physical trails. The forager walking speed on physical trails had an increment of 86.10%. These significant increments might be related to the truly narrow corridor present inside physical trails that are leaf litter-free, and thereby chemically stronger and smoother than non-physical ones. The speed improvement could induce the construction of longer trails which guide the workers more efficiently to the foraging patch. Thus, physical trails have an important role in foraging efficiency as they allow workers go quickly and further to forage, since they limit a path and congregate more individuals, raising the leaf delivery rate. This study provides additional information about foraging trails of leaf-cutting ants

Comparison of the Ant Assemblages in Three Phytophysionomies: Rocky Field, Secondary Forest, and Riparian Forest-A Case Study in the State Park of Ibitipoca, Brazil

Ant assemblages are almost all related with the vegetation composition and so can provide us important information for conservation strategies, which are especially relevant to an environmentally protected area. We sampled the ant fauna in three different phytophysionomies in order to verify if the composition of ant species is different among the areas, especially because one of the areas is a Rocky Field and there is little information about the ant fauna in this habitat. A total of 8730 individuals were registered and an NMDS analysis showed that the ant assemblies are different at the three phytophysionomies (Rocky Field, Riparian Forest, and Secondary Forest). This study shows that the species that compose the ant assemblies in different phytophysionomies are a reflex of the environment, supporting the hypothesis that the vegetational composition results in different compositions in the ant assembly. Vegetal composition is determinant in the formation of the litter and consequently in the occurrence of ant species that depend on this layer of organic matter for nesting and foraging

Novas perspectivas sobre a ocorrência do comportamento de caroneira

(New perspectives of hitchhiking behavior occurrence). During foraging of leafcutting ants, it can be observed minimal workers over leaf fragments, called hitchhikers. Many functions are cited as related with hitchhiking behavior, as defense against parasitoids, leaf cleaning, energy saving and sap feeding. Here, the objectives were to evaluate i) if hitchhiker occurrence is plant-size-species-dependent, ii) if microbial load influences hitchhiker frequency and iii) how hitchhiker frequency is influenced by high density of foraging traffic. It has been manipulated leaf fragments and foraging trails. In first experiment, it has been verified that hitchhikers could occur over any fragment size or plant species, but hitchhiker masses varied among plant species. In the second experiment, the entomopathogenic fungus and antibiotics reduced hitchhiker occurrence. Thus, it was not possible to relate hitchhiker frequency with microbial load removal. It has been suggested that hitchhikers avoid the conidia fungal and the antibiotic solutions due to these materials are unknown by workers. In the third experiment, hitchhiker frequency has been higher at narrow trails, which has greater worker density. Actually, hitchhiker frequency has been positively correlated with the outbound worker flow in the three experiments. Due to high head-on encounters promoted by the increased outbound worker flow and by the greater worker density in narrow trails, it has been suggested that hitchhiker behavior is stimulated by these encounters, which are regulatory agents of task allocation. The hitchhiker behavior could be considered a behavioral strategy to reduce worker traffic along foraging trails.(Novas perspectivas sobre a ocorrência do comportamento de caroneira). Durante o forrageamento de formigas cortadeiras pode-se observar operárias mínimas sobre os fragmentos de folha transportados até o ninho, comportamento denominado de caroneira. São citadas várias funções relacionadas a este comportamento, como defesa contra forídeos parasitoides, limpeza dos fragmentos de folhas, economia de energia de retono ao ninho, além de ingestão de seiva que exsuda do corte. Sendo assim, o presente estudo se apresenta como uma forma de elucidar questões ecológico-comportamentais de caroneira em Acromyrmex subterraneus, tendo por objetivos avaliar i) se as caroneiras ocorrem de forma aleatória ou dependente do fragmento vegetal transportado, ii) se a carga microbiana influencia a frequência de caroneiras e iii) como as caroneiras respondem a variações no tráfego de forrageamento. Para tanto, foram feitas manipulações nos fragmentos vegetais oferecidos e nas trilhas de forrageamento. No primeiro experimento verificou-se que caroneiras podem ocorrer em qualquer tamanho de fragmento ou espécie vegetal, mas há variação do tamanho da caroneira em função do fragmento. Tal fato demonstra alta plasticidade deste comportamento, de forma a ocorrer sobre os mais diversos substratos. No segundo experimento a presença de fungo entomopatogênico e antibióticos diminuiu a ocorrência de caroneiras, não sendo possível relacionar a frequência de caroneiras com a remoção de carga microbiana. Sugere-se que as caroneiras tenham evitado contato com os conídios fúngicos e com as soluções antimicrobianas porque eram substâncias desconhecidas pelas operárias. Já no terceiro experimento observou-se incremento da frequência de caroneiras em trilha estreita, com alta densidade de operárias. De fato, a frequência de caroneiras se correlacionou positivamente com o fluxo de operárias que deixavam o ninho nos três experimentos. Devido à alta frequência de encontros promovida pelo aumento do fluxo de operárias que saem do ninho e da densidade de operárias na trilha estreita sugere-se que o comportamento de caroneira é estimulado por esta taxa de encontros, que é agente regulatório de alocação de tarefas. O comportamento de caroneira pode ser considerado uma estratégia comportamental para redução do tráfego de operárias nas trilhas

Novas perspectivas sobre a ocorrência do comportamento de caroneira

(Novas perspectivas sobre a ocorrência do comportamento de caroneira). Durante o forrageamento de formigas cortadeiras pode-se observar operárias mínimas sobre os fragmentos de folha transportados até o ninho, comportamento denominado de caroneira. São citadas várias funções relacionadas a este comportamento, como defesa contra forídeos parasitoides, limpeza dos fragmentos de folhas, economia de energia de retono ao ninho, além de ingestão de seiva que exsuda do corte. Sendo assim, o presente estudo se apresenta como uma forma de elucidar questões ecológico-comportamentais de caroneira em Acromyrmex subterraneus, tendo por objetivos avaliar i) se as caroneiras ocorrem de forma aleatória ou dependente do fragmento vegetal transportado, ii) se a carga microbiana influencia a frequência de caroneiras e iii) como as caroneiras respondem a variações no tráfego de forrageamento. Para tanto, foram feitas manipulações nos fragmentos vegetais oferecidos e nas trilhas de forrageamento. No primeiro experimento verificou-se que caroneiras podem ocorrer em qualquer tamanho de fragmento ou espécie vegetal, mas há variação do tamanho da caroneira em função do fragmento. Tal fato demonstra alta plasticidade deste comportamento, de forma a ocorrer sobre os mais diversos substratos. No segundo experimento a presença de fungo entomopatogênico e antibióticos diminuiu a ocorrência de caroneiras, não sendo possível relacionar a frequência de caroneiras com a remoção de carga microbiana. Sugere-se que as caroneiras tenham evitado contato com os conídios fúngicos e com as soluções antimicrobianas porque eram substâncias desconhecidas pelas operárias. Já no terceiro experimento observou-se incremento da frequência de caroneiras em trilha estreita, com alta densidade de operárias. De fato, a frequência de caroneiras se correlacionou positivamente com o fluxo de operárias que deixavam o ninho nos três experimentos. Devido à alta frequência de encontros promovida pelo aumento do fluxo de operárias que saem do ninho e da densidade de operárias na trilha estreita sugere-se que o comportamento de caroneira é estimulado por esta taxa de encontros, que é agente regulatório de alocação de tarefas. O comportamento de caroneira pode ser considerado uma estratégia comportamental para redução do tráfego de operárias nas trilhas.(New perspectives of hitchhiking behavior occurrence). During foraging of leafcutting ants, it can be observed minimal workers over leaf fragments, called hitchhikers. Many functions are cited as related with hitchhiking behavior, as defense against parasitoids, leaf cleaning, energy saving and sap feeding. Here, the objectives were to evaluate i) if hitchhiker occurrence is plant-size-species-dependent, ii) if microbial load influences hitchhiker frequency and iii) how hitchhiker frequency is influenced by high density of foraging traffic. It has been manipulated leaf fragments and foraging trails. In first experiment, it has been verified that hitchhikers could occur over any fragment size or plant species, but hitchhiker masses varied among plant species. In the second experiment, the entomopathogenic fungus and antibiotics reduced hitchhiker occurrence. Thus, it was not possible to relate hitchhiker frequency with microbial load removal. It has been suggested that hitchhikers avoid the conidia fungal and the antibiotic solutions due to these materials are unknown by workers. In the third experiment, hitchhiker frequency has been higher at narrow trails, which has greater worker density. Actually, hitchhiker frequency has been positively correlated with the outbound worker flow in the three experiments. Due to high head-on encounters promoted by the increased outbound worker flow and by the greater worker density in narrow trails, it has been suggested that hitchhiker behavior is stimulated by these encounters, which are regulatory agents of task allocation. The hitchhiker behavior could be considered a behavioral strategy to reduce worker traffic along foraging trails

Comportamento de caroneiras e suas implicações no forrageamento de Acromyrmex subterraneus subterraneus (Forel, 1893)

Foraging trails of leaf-cutting ants are composed by a great number of workers of different sizes also performing many different acts. Their behavior is related with the cut and transport of leaves to the nest, as well as the trail maintenance and defense. Minimal workers are commonly observed hitchhiking the transported fragments, well-known behavior for Atta, but still not investigated for Acromyrmex. Some reported data relate the occurrence of this behavior with the defense against parasitoids and the cleaning and preparation of the leaf before being incorporated in the fungus garden. In this context, hitchhikers promote an increase at the foraging efficiency. On the other hand, the hitchhiker behavior is also related with the ingestion of exuded sap from the leaves fragments, with lower energy expend for moving between the nest and the resource or just to the fact that the workers could not get down of the fragments. In this situation, hitchhiking could represent an extra cost for the forager workers reducing its individual foraging efficiency. Although this behavior is not observed in all types of fragments transported, their role during foraging is still not well explained as well as which factors stimulate their occurrence. Our objective was to develop an ethogram in order to relate the posture of the hitchhikers with their function; to evaluate the effect of hitchhikers presence on the running speed and colony's foraging efficiency; to investigate the frequency of hitchhikers over plant fragments of different sizes and types, and to check the relationship between the size of the transported fragment with the permanence time of hitchhikers over the leaves. Results indicate that hitchhikers are vigilant and keep over the fragment in order to reduce the impact of their presence. This supposition is based on our results that show a negative influence of the hitchhikers on the running speed and individual foraging efficiency. Hitchhikers increase vigilance during foraging, and although they represent a cost to the forager, this cost is probably offset by a defense increase. Also, the frequency of hitchhikers on different substrates suggests that they are able to choose the type of substrate on which they will climb. Their higher frequency in A. wilkesiana leaves than in petals of Rosa sp. could be related with the largest number of trichomes, that can serve as support, and largest number of vascular bundles, that increased hardness of the substrate. The higher frequency of hitchhikers over bigger fragments of A. wilkesiana must be related to a bigger patrolling area and more exuded sap. Hitchhikers behavior could also be triggered by phorids presence at foraging trails. However, parasitoids presence turn the fragments size smaller due to the fact that smaller foragers cut smaller fragments. But the size could not be too much reduced allowing the occurrence of hitchhikers. Thus, minimal workers present at the foraging trails must forage close to their optimal foraging, carrying large fragments. So, foragers have higher energy expenditure, but adjust the size and type of plant substrate so that the occurrence of hitchhikers is maximized, allowing that minimal workers climb on the leaves and engaged in the defense against phorid parasitoids.Nas trilhas de forrageamento de formigas cortadeiras são encontradas operárias de diferentes classes de tamanho que desempenham várias funções relacionadas ao corte e transporte de folhas para o ninho, bem como de manutenção e defesa da trilha. Operárias da casta mínina podem ser comumente observadas “pegando carona” nos fragmentos transportados, ato bastante conhecido para Atta (saúvas), mas ainda pouco estudado para Acromyrmex (quemquéns). Na literatura dados relacionam a ocorrência deste comportamento com a defesa contra parasitóides e com a limpeza e preparo da folha para incorporação no jardim de fungo. Nesta situação, a ocorrência das caroneiras promoveria um incremento na eficiência do forrageamento. Por outro lado, o ato de pegar carona também se relaciona com a ingestão de seiva exsudada do fragmento, com menor custo energético para locomoção entre ninho e recurso ou ainda com o simples fato que as operárias não conseguem descer dos fragmentos. Neste caso, o ato de “pegar carona” pode representar um custo extra para a forrageira que a transporta reduzindo sua eficiência individual no forrageamento. Apesar deste comportamento não ser observado em todos os fragmentos transportados, seu papel durante o forrageamento ainda não está bem esclarecido, bem como dos fatores estimulam sua ocorrência. Sendo assim, objetivou-se elaborar um etograma das caroneiras a fim de relacionar suas atitudes comportamentais com a provável finalidade de sua ocorrência; avaliar o efeito da presença de caroneiras sobre a velocidade de deslocamento e a eficiência do forrageamento individual das forrageiras; investigar a frequência de caroneiras em fragmentos vegetais de diferentes tamanhos e tipos; e verificar se há relação entre o tamanho do fragmento transportado com o tempo de permanência das caroneiras sobre as folhas. O etograma obtido indica que as caroneiras são vigilantes e sugere-se que elas se mantêm no fragmento de forma a diminuir o impacto de sua presença sobre a forrageira que a transporta. Tal suposição está embasada visto que a ocorrência de caroneiras influencia negativamente na velocidade de deslocamento e na eficiência individual da forrageira que a transporta. Caroneiras aumentam a vigilância durante o forrageamento e embora representem um custo individual à forrageira transportadora, este custo é provavelmente compensado pelo incremento na defesa e reduzido pela atitude comportamental mantida sob a folha. A frequência de caroneiras nos diferentes substratos sugere que elas são hábeis em discriminar o tipo de substrato no qual irão subir. A maior freqüência de caroneiras em folhas de Acalypha wilkesiana que em pétalas de Rosa sp. pode estar relacionado com a presença de tricomas nas folhas, que podem servir como ponto de apoio, e com a presença de mais feixes vasculares nas folhas, que deve conferir maior dureza à folha. O maior número de caroneiras em fragmentos grandes de A. wilkesiana deve estar relacionado com maior área de patrulhamento da caroneira e maior área exsudando seiva. A ocorrência de caroneiras também pode ser disparada pela presença de forídeos nas trilhas de forrageamento. Entretanto, a presença de parasitóides diminui o tamanho das operárias forrageiras, diminuindo em consequência, o tamanho do fragmento transportado. Porém, deve haver um limite mínimo de tamanho de fragmento para que a condição de caroneira seja exercida. Dessa forma, as operárias menores presentes nas trilhas devem forragear próximo ao ótimo, transportando fragmentos grandes. Assim, as forrageiras teriam alto gasto energético, mas ajustariam o tamanho e o tipo de substrato vegetal de modo que a ocorrência de caroneiras seja maximizada, permitindo que as mínimas subam nas folhas e exerçam a defesa das operárias contra forídeos parasitóides

A convenient trip: an analysis of the impact of Hitchhiker ants on forager transport rates

During foraging, leaf-cutting ant workers of different size classes perform various tasks along foraging trails. Commonly, small workers called hitchhikers climb on leaf fragments imposing an extra transport cost, so their presence is thought to reduce the individual foraging performance. There are four main hypotheses which may explain the occurrence of hitchhikers and a different behavioral act related to their role can be predicted for each. Hitchhiker behavior was observed considering these hypotheses and the effect of the hitchhikers on the walking speed and transport rate of foragers was evaluated. The behavioral registers were obtained from 1371 hitchhikers on foraging trails of Acromyrmex subterraneus subterraneus nests in the field. To verify the influence of hitchhikers on walking speed and transport rate, 239 foragers with hitchhikers and 250 foragers transporting only leaf fragments were analyzed. The walking speed, burden and transport rate of each forager were calculated. Data indicated not only that hitchhikers are vigilant but that they remain motionless on the leaf fragment probably in order to reduce the impact of their presence for the loaded forager. The impact of their presence is verified through walking speed reduction but as they ride preferentially on larger workers who transport larger leaf fragments, there are no losses in the individual transport rate. The transporter selection made by the hitchhiker ensures at the same time enhanced protection against phorid parasitoids and the maintenance of the leaf transport rate

Influencia de la elaboración de pronósticos de demanda en los costos de la empresa Darbha SAC, Cajamarca - 2017

RESUMEN La Empresa DARBHA S.A.C se dedica a brindar servicios de educación universitaria a nivel de postgrado, investigación, capacitación de personas del sector público y privado, organización de eventos educativos y culturales de forma presencial, semipresencial y a distancia. Esta empresa no contaba con un estudio de pronóstico de demanda de los cursos y/o diplomados que ofrece, por lo se registra pérdidas económicas en algunos diplomados al no conseguir la demanda esperada. Para ello se realizó una investigación donde se determinó la influencia de pronósticos de la demanda en los costos de la empresa DARBHA SAC, teniendo un diseño de investigación transversal correlacional. Se identificó el comportamiento de los costos en el historial de la empresa donde se pudo observar que hay una tienen una tendencia periódica cada tres meses con respecto a la demanda de matriculados, se determinó la metodología apropiada para pronosticar la demanda de la empresa, se pronosticó la demanda para ocho periodos siguientes mediante el método de serie de tiempos usando el Minitab, con un punto de equilibrio de veinte matriculados. Como resultado para poder verificar la viabilidad del proyecto se realizó la valoración económica obteniendo un WACC del 8.06%, el cual nos indica que la propuesta es viable. Con lo antes mencionado se puede concluir que el pronóstico de demanda influye considerablemente en los costos de la empresa, además de tener una relación significativa, con un R = 0.9 se logró determinar que la elaboración de pronóstico de la demanda y los costos de la empresa se relacionan significativamente. PALABRAS CLAVE: Pronósticos, influencia, costos, demanda, serie de tiempos.ABSTRACT The Company DARBHA S.A.C is dedicated to providing university education services at postgraduate level, research, training of people from the public and private sector, organization of educational and cultural events in person, in person and at a distance. This company did not have a demand forecast study of the courses and / or diplomas offered, so there are economic losses in some graduates by not achieving the expected demand. For this, a research was carried out where the influence of demand forecasts on the costs of DARBHA SAC was determined, having a correlational cross-sectional research design. It was identified the behavior of the costs in the history of the company where it was possible to observe that there is a periodic tendency every three months with respect to the demand of enrolled ones, it was determined the appropriate methodology to predict the demand of the company, it was predicted the demand for eight following periods using the time series method using the Minitab, with a break-even point of twenty enrolled. As a result, to verify the feasibility of the project, the economic valuation was obtained, obtaining a WACC of 8.06%, which indicates that the proposal is viable. With the aforementioned, it can be concluded that the forecast of demand influences considerably the costs of the company, in addition to having a significant relation, with R2 = 0.9 it was possible to determine that the elaboration of forecast of the demand and the costs of the company are significantly relat