Ecology and Evolutionary Biology

Cellular slime molds, including the well-studied Dictyostelium discoideum, are amoebae whose life cycle includes both a single-cellular and a multicellular stage. To achieve the multicellular stage, individual amoebae aggregate upon starvation to form a fruiting body made of dead stalk cells and reproductive spores, a process that has been described in terms of cooperation and altruism. When amoebae aggregate they do not perfectly discriminate against nonkin, leading to chimeric fruiting bodies. Within chimeras, complex interactions among genotypes have been documented, which should theoretically reduce genetic diversity. This is however inconsistent with the great diversity of genotypes found in nature. Recent work has shown that a little-studied component of D. discoideum fitness-the loner cells that do not participate in the aggregation-can be selected for depending on environmental conditions and that, together with the spores, they could represent a bet-hedging strategy. We suggest that in all cellular slime molds the existence of loners could resolve the apparent diversity paradox in two ways. First, if loners are accounted for, then apparent genotypic skew in the spores of chimeras could simply be the result of different investments into spores versus loners. Second, in an ecosystem with multiple local environments differing in their food recovery characteristics and connected globally via weak-to-moderate dispersal, coexistence of multiple genotypes can occur. Finally, we argue that the loners make it impossible to define altruistic behavior, winners or losers, without a clear description of the ecology.

In East Africa fire and grazing by wild and domestic ungulates maintain savannas, and pastoralists historically set fires and herded livestock through the use of temporary corrals called bomas. In recent decades traditional pastoral practices have declined, and this may be affecting biodiversity. We investigated the effects of prescribed fires and bomas on savanna bird communities in East Africa during the first and second dry seasons of the year (respectively before and after the rains that mark the onset of breeding for most birds). We compared abundance, richness, and community composition on 9-ha burned plots, recently abandoned bomas, and control plots in the undisturbed matrix habitat over a 3-year period. Generally, recently burned areas and abandoned bomas attracted greater densities of birds and had different community assemblages than the surrounding matrix. The effects of disturbances were influenced by interactions between primary productivity, represented by the normalized difference vegetation index, and time. Bird densities were highest and a greater proportion of species was observed on burned plots in the months following the fires. Drought conditions equalized bird densities across treatments within 1 year, and individuals from a greater proportion of species were more commonly observed on abandoned bomas. Yearly fluctuations in abundance were less pronounced on bomas than on burns, which indicate that although fire may benefit birds in the short term, bomas may have a more-lasting positive effect and provide resources during droughts. Several Palearctic migrants were attracted to burned plots regardless of rainfall, which indicates continued fire suppression may threaten their already-declining populations. Most notably, the paucity of birds observed on the controls suggests that the current structure of the matrix developed as a result of fire suppression. Traditional pastoralism appears critical to the maintenance of avian diversity in these savannas.

The Bush Pipit Anthus caffer is a partly nomadic African species whose movements coincide with the onset of rains. Across the continent, the distribution and geographic extent of the five Bush Pipit subspecies are poorly known. In Kenya, the documented range of the Bush Pipit is along the Tanzanian border in the southwest of the country. We provide evidence of a previously undocumented population of Bush Pipits in Laikipia District, Central Kenya that may have been overlooked due to difficulty in identifying this species. It appears that this population may constitute a seasonal influx related to an increase in local primary productivity. However, we also provide preliminary evidence that this species may breed in Laikipia during December–January, while it has been reported that it breeds during March–April in Kenya. Nonetheless, we could not completely ascertain based on this short study whether or not Bush Pipits are year-round residents in Laikipia.

In East Africa fire and grazing by wild and domestic ungulates maintain savannas, and pastoralists historically set fires and herded livestock through the use of temporary corrals called bomas. In recent decades traditional pastoral practices have declined, and this may be affecting biodiversity. We investigated the effects of prescribed fires and bomas on savanna bird communities in East Africa during the first and second dry seasons of the year (respectively before and after the rains that mark the onset of breeding for most birds). We compared abundance, richness, and community composition on 9-ha burned plots, recently abandoned bomas, and control plots in the undisturbed matrix habitat over a 3-year period. Generally, recently burned areas and abandoned bomas attracted greater densities of birds and had different community assemblages than the surrounding matrix. The effects of disturbances were influenced by interactions between primary productivity, represented by the normalized difference vegetation index, and time. Bird densities were highest and a greater proportion of species was observed on burned plots in the months following the fires. Drought conditions equalized bird densities across treatments within 1 year, and individuals from a greater proportion of species were more commonly observed on abandoned bomas. Yearly fluctuations in abundance were less pronounced on bomas than on burns, which indicate that although fire may benefit birds in the short term, bomas may have a more-lasting positive effect and provide resources during droughts. Several Palearctic migrants were attracted to burned plots regardless of rainfall, which indicates continued fire suppression may threaten their already-declining populations. Most notably, the paucity of birds observed on the controls suggests that the current structure of the matrix developed as a result of fire suppression. Traditional pastoralism appears critical to the maintenance of avian diversity in these savannas.

The Bush Pipit Anthus caffer is a partly nomadic African species whose movements coincide with the onset of rains. Across the continent, the distribution and geographic extent of the five Bush Pipit subspecies are poorly known. In Kenya, the documented range of the Bush Pipit is along the Tanzanian border in the southwest of the country. We provide evidence of a previously undocumented population of Bush Pipits in Laikipia District, Central Kenya that may have been overlooked due to difficulty in identifying this species. It appears that this population may constitute a seasonal influx related to an increase in local primary productivity. However, we also provide preliminary evidence that this species may breed in Laikipia during December–January, while it has been reported that it breeds during March–April in Kenya. Nonetheless, we could not completely ascertain based on this short study whether or not Bush Pipits are year-round residents in Laikipia.

The first part of this thesis consists of three chapters outlining a theory of the emergence of linear dominance hierarchies. The first chapter provides the necessary background and lays out the argument for the approach I have taken which is to make a mechanistic model, embed it within an evolutionary framework, and then to begin to test it using a model species. In the second chapter, I present the model of decision-making during animal contests which lies at the core of the theory. It is based on the sequential probability ratio test which is a standard decision-making mechanism. I outline the predictions of the model and in particular draw attention to the speed-accuracy trade-off faced by animals as they contest resources. In the third chapter, I extend this model to incorporate the use of prior information during decision-making. Individuals observe fights between other group-members and use the evidence they acquire from these to inform their decisions in future contests. The use of prior information in this way explains both the ‘bystander effect’, whereby individuals are more likely to lose against others they have seen win and vice versa, and the emergence of linear hierarchies at the level of the group. Armed with a model of how hierarchies form, I am then able to make novel predictions about how resource distributions affect their emergence and to suggest methods for manipulating the level of equality in groups.

The second part of this thesis is devoted to developing a model species for testing the theory outlined in the first part. I focus on the zebrafish (Danio rerio) for three reasons: first, it is such a well-established model system that tools exist to test the predictions of the model at the neural level; second, the fish are small enough to keep in the laboratory in large numbers and third, they have relatively few degrees of physical freedom, which simplifies the classification of its behavior. The first step to testing the theory is to establish that the behavior of the animals in individual contests conforms to the predictions of the assessment model. The methodology for testing between models of contest behavior has lagged behind developments in model selection, so in the first chapter of this part of the thesis I illustrate how this technique can simply and accurately discriminate between two different mechanisms of decision-making. In order to reach the widest possible audience I make use of the predictions of two existing models of contests, the war of attrition and the sequential assessment model, rather than my own version of the mutual assessment model.

In the second chapter, I outline the results of my studies of contests between male zebrafish. To my knowledge, zebrafish fighting behavior has not been studied before, and I find that they engage in highly stereotyped ritualized contests with a clear winner and loser. I establish metrics of both resource holding potential (RHP) and contest duration and use these data to select the model most likely to describe their decision-making. I compare the ability of three broad classes of mechanism to predict these data, mutual assessment (which is modeled in chapter 2), self-assessment and cumulative assessment. I find that zebrafish are most likely to use a process of mutual assessment to decide the outcome of contests. This confirms that they are using the mechanism upon which the model in chapter 3 is built, and so the way is now open to use them as a model species to search for the neural populations corresponding to the decision variable or to test the predictions of the model at the group level.

The final part of this thesis is devoted to relaxing the assumption that animals have only a single currency in which they can invest in the accuracy of their decisions. In reality, the costs of accuracy come from many different sources. Some of these sources, such as predation risk, may vary in magnitude in a fashion uncorrelated with others, such as the cost of energetic expenditure: the cost of a minute of information gathering may rise in the presence of a snake or when you are hungry, but these two may not be correlated with one another. I use a simple model based on the sequential probability ratio test to show that when an animal has two currencies available, which I call time and effort, it should substitute between them as their relative costs vary. An animal with this ability gains an advantage along both axes of the traditional speed-accuracy trade-off, making more accurate decisions at a lower cost. I outline a set of testable predictions that would allow researchers to uncover the trade-off between speed, effort and accuracy in action.

One possible situation in which this trade-off may operate is within animal contests. If behaviors deployed early in contests (such as visual assessment) cost less than those deployed at greater levels of escalation (such as biting) but are also less informative about RHP differences, then individuals may escalate more slowly in situations where time is cheap relative to effort, and more quickly when time is expensive.

The three parts of this thesis together form a coordinated attempt to advance an information-based theory of fighting and dominance in animal societies based on the way in which animals make their decisions. I suggest that of all the factors affecting contest outcomes, it is what animals learn about one another that is the most important for the emergence of social hierarchies. This is an old idea, but one whose time has now come with the advent of more powerful approaches to modeling decision-making, and I hope that it will eventually lead to a predictive theory of social structure firmly grounded in ecology and evolution.

The standard view in biology is that all animals, from bumblebees to human beings, face a trade-off between speed and accuracy as they search for resources and mates, and attempt to avoid predators. For example, the more time a forager spends out of cover gathering information about potential food sources the more likely it is to make accurate decisions about which sources are most rewarding. However, when the cost of time spent out of cover rises (e.g. in the presence of a predator) the optimal strategy is for the forager to spend less time gathering information and to accept a corresponding decline in the accuracy of its decisions. We suggest that this familiar picture is missing a crucial dimension: the amount of effort an animal expends on gathering information in each unit of time. This is important because an animal that can respond to changing time costs by modulating its level of effort per-unit-time does not have to accept the same decrease in accuracy that an animal limited to a simple speed-accuracy trade-off must bear in the same situation. Instead, it can direct additional effort towards (i) reducing the frequency of perceptual errors in the samples it gathers or (ii) increasing the number of samples it gathers per-unit-time. Both of these have the effect of allowing it to gather more accurate information within a given period of time. We use a modified version of a canonical model of decision-making (the sequential probability ratio test) to show that this ability to substitute effort for time confers a fitness advantage in the face of changing time costs. We predict that the ability to modulate effort levels will therefore be widespread in nature, and we lay out testable predictions that could be used to detect adaptive modulation of effort levels in laboratory and field studies. Our understanding of decision-making in all species, including our own, will be improved by this more ecologically-complete picture of the three-way tradeoff between time, effort per-unit-time and accuracy.

Resumen El presente escrito es un corto recuento histórico de la ornitología en Colombia desde finales del siglo XVIII hasta el presente. Este abarca desde las primeras aves descritas a partir de ejemplares de Colombia, las primeras expediciones, personajes y colectas que dieron lugar al conocimiento de las aves; hasta muchos de los museos y colecciones biológicas que se crearon y aun hoy persisten. Posteriormente se reseña como se documentó la diversidad de aves gracias a exploraciones a diferentes regiones y al impulso de diferentes instituciones y personas que más tarde dieron lugar a la formación de escuelas ornitológicas. Estas escuelas permitieron el surgimiento de las asociaciones, fundaciones y sociedades ornitológicas que han fomentado y apoyado no solo el estudio e interés en las aves sino también su conservación y admiración. Por ultimo, se señalan algunos vacíos del conocimiento en aves colombianas, los cuales podemos abordar más fácilmente desde nuestro momento histórico al entender el contexto que ha influido en su desarrollo. Palabras clave: aves, colecciones de historia natural, Colombia, ornitología, Suramérica. Abstract A brief historical account of colombian ornithology from the XVII century to present is presented. This account includes the first described species from colombian birds, the first expeditions, researchers and collections that were responsible for the development of our knowledge on birds, as well as many of the museums and natural history collections created at the time and that still persist today. A quick overview is given on how bird diversity was studied through the exploration of different geographic regions by key researchers and institutions that later made possible the development of ornithological schools. These schools have made possible the establishment of ornithological societies and research institutions that promote and support the conservation and awareness of birds through the study of and interest in them. Finally, some gaps in the knowledge of colombian birds are identified in the hopes that we can tackle them, drawn on our understanding of the historical context and development of Colombian ornithology.

Ornitología Colombiana No.7 (2008):66-74 66 Las rapaces grandes (géneros Harpia, Morphnus, Spizaetus y Harpyaliaetus) son un componente es-pecialmente sensible de la avifauna neotropical, ya que por ser cazadoras de vertebrados vivos para cubrir sus necesidades alimenticias, requieren de áreas de gran tamaño para obtener el alimento sufi-ciente, utilizando generalmente hábitats en buen estado de conservación (Thiollay 1991, Kattan et al. 1994). Dentro de estas mismas áreas, las rapaces grandes llevan a cabo otros procesos como la repro-ducción (necesitando de árboles de gran porte para anidar), defensa del territorio e incluso la disper-sión de juveniles. La situación anterior implica que todas estas especies tienden a ser poco abundantes y a presentar densidades muy bajas (son raras) na-turalmente, por lo cual es muy poco el conocimien-to biológico y ecológico que se tiene de ellas. En esta nota presentamos nueva información sobre dos Dirección Actual: 1 Department of Ecology and Evolutionary Biology, Guyot Hall, Princeton University, Princeton New Jersey USA. 2 Asociación para el Estudio y Conservación de las Aves Acuáticas en Colombia, CALIDRIS. Cali, Colombia. Notas cortas RESUMEN Presentamos cuatro nuevos registros de distribución para dos especies de águilas (Accipitridae) que constituyen ampliaciones a las distribuciones anteriormente reportadas en Colombia. Un ejemplar juvenil del Águila Crestada Spizaetus isidori fue obtenido mientras que otro individuo fue observado en el departamento de Norte de Santander, un individuo adulto fue observado en el departamento del Tolima, y un tercer registro para esta especie se obtuvo en Caldas. Para el Águila Iguanera S. tyrannus, dos individuos fueron observados en el departamento del Valle del Cauca, registro que además representa una ampliación de su rango altitudinal. Se presentan dos figuras y anotaciones para la identificación de adultos y juveniles al vuelo de S. tyrannus. ABSTRACT We present four new distributional records for two species of eagles (Accipitridae), which constitute extensions of their known distributions in Colombia. A juvenile specimen of the Black-and-chestnut Eagle Spizaetus isidori was obtained while an adult was seen in the department of Norte de Santander, another adult individual was seen in the department of Tolima, and a third record for this species was obtained at Caldas. Two individuals of the Black Hawk-Eagle S. tyrannus were observed in the Valle del Cauca department, at higher elevations than previously reported for Colombia. Two figures with notes are presented as an aid to identify adults and juveniles of S. tyrannus in flight.

Background: Zoonotic infections pose a significant public health challenge for low-and middle-income countries and have traditionally been a neglected area of research. The Roadmap to Combat Zoonoses in India (RCZI) initiative conducted an exercise to systematically identify and prioritize research options needed to control zoonoses in India.

Governments and NGOs worldwide aim to develop models of tourism that realize the economic, environmental, and cultural ideals of ecotourism. This is true in the national parks of the Northern Safari Circuit of Tanzania, which attract hundreds of thousands of tourists annually. To better understand what tourists to Tanzania were willing to pay for various attributes of their tour package, we used a linear mixed effects model to analyze what attributes of 72 tour packages from 32 tour operators contributed to the price of tour packages. We found that the number of days spent on tour, the number of days spent in the Serengeti, the type of accommodation (basic camping versus lodges or luxury tents), the mode of transport into the park (flying versus driving), and the inclusion of cultural tourism helped predict the price of a tour package. Our findings suggest that tour operators charge 92% more for a day in the Serengeti than other Northern Circuit attractions, but we do not examine what happens to the additional rent generated by the Serengeti. Additionally, the utility of cultural tourism in attracting foreign tourists presents both tremendous opportunities and potential challenges to efforts to realize culturally sensitive ecotourism.

1. Large animals are disproportionately likely to go extinct, and the effects of this on ecosystem processes are unclear. Megaherbivores (weighing over 1000 kg) are thought to be particularly effective seed dispersers, yet only a few plant species solely or predominantly adapted for dispersal by megaherbivores have been identified. 2. The reasons for this paradox may be elucidated by examining the ecology of so-called megafaunal fruiting species in Asia, where large-fruited species have been only sparsely researched. We conducted focal tree watches, camera trapping, fruit ageing trials, dung seed counts and germination trials to understand the ecology of Dillenia indica, a large-fruited species thought to be elephant-dispersed, in a tropical moist forest (Buxa Tiger Reserve, India). 3. We find that the initial hardness of the fruit of D. indica ensures that its small (~6 mm) seeds will primarily be consumed and dispersed by elephants and perhaps other megaherbivores. Elephants removed 63.3% of camera trap-monitored fruits taken by frugivores. 4. If the fruit of D. indica is not removed by a large animal, the seeds of D. indica become available to successively smaller frugivores as its fruits soften. 5. Seeds from both hard and soft fruits are able to germinate, meaning these smaller frugivores may provide a mechanism for dispersal without megaherbivores. 6. Synthesis. Dillenia indica's strategy for dispersal allows it to realize the benefits of dispersal by megaherbivores without becoming fully reliant on these less abundant species. This risk-spreading dispersal behaviour suggests D. indica will be able to persist even if its megafaunal disperser becomes extinct.