Macalester Reviews in Biogeography

Revisiting the Intricacies and Theories of the Island Rule: Understanding the Trends of Insular Body Size Evolution

Lam (Peter) Bao — Tue, 31 May 2011 06:17:12 PDT

The Island Rule is the observed tendency for island isolated animals to either grow or shrink in size compared to their mainland counterparts. Though the phenomenon was initially observed to only occur in a handful of taxa (carnivores, artiodactyls, rodents, and lagomorphs), it was expanded to include 2 major trends: 1) Large animals from the mainland tend to shrink on islands, and 2) Small animals from the mainland tend to grow. The mechanisms attributed to those two trends generally involved factors that include resource availability, ecological release, niche expansion, predation, competition, and life history traits. Other theories were also proposed, but each had their own caveats that did not apply as a general rule. The study of the island rule, and island biogeography in general, allows a simplified view of dynamics that may possibly be reflected on mainlands. An example of this includes ecological release and niche expansion in the case of mammals following the Cretaceous/Tertiary extinction event. Following the collapse of dinosaurian prevalence, the relatively small mammals were given the opportunity to grow and speciate accordingly.

However, upon further observation, the island rule in its generality did not encompass all fauna, and exceptions were found for the insular trend. Bergmann’s rule of latitudinal differentiation for body sizes, as well as general climate change, have been found to potentially influence body size shifts as well. As a result, some have chosen to strip the Island Rule of its status as a virtual law, and instead explain the trend as being a phenomenon greatly affected by both biotic and abiotic components to determine insular body size. Regardless of the specific definition, it is maintained that a strong understanding of island processes may lend a better understanding of mainland developmental ecology and evolution.

The Fate of Alpine Species in the Face of Climate Change: A Biogeographic Perspective

Madaline Cochrane — Fri, 06 May 2011 07:23:03 PDT

Will global climate change affect the spatial distribution and abundance of biodiversity along mountains equally? The elevational gradients inherent as one moves up a mountain slope help define the many biological patterns that emerge as key indicators for species richness in an era of rising global temperatures. When global temperatures arise, the microclimates found along different elevational ranges on mountains also fluctuate. As abiotic characteristics such as daily air temperature, daily precipitation, and annual snowmelt change overtime, so will the biotic communities on a mountain. Some species may be able to adapt to their new environments, while other may have the capacity to shift their ranges upward. However, the biological realities facing mountain species vary given the elevational and life history characteristics of each individual species. This review paper summarizes many of the major biogeographical patterns that have been observed to occur on elevational gradients as a result of global warming. This is by no means an all-inclusive report on the state of scientific knowledge in this important field, but instead a discussion of the varied ecological realities facing biota along mountains throughout the world.

Deep-Sea Hydrothermal Vent Fauna: Evolution, Dispersal, Succession and Biogeography

Alexander Howe — Fri, 08 May 2009 08:03:47 PDT

Since their discovery in 1977, the ecological communities found at deep-sea hydrothermal vents have provided many surprises about life on Earth in extreme conditions and continue to instill much curiosity in scientists that study their systems as well as those simply interested in Earthʼs biodiversity. This review paper will attempt to provide a general overview of as many aspects of hydrothermal vents and their associated fauna as possible. The general geological processes that produce these systems and the chemosynthesis which sustains abundant life at these depths will first be covered. A basic overview of hydrothermal vent ecology, including some key organisms and general succession patterns will be taken up next. Dispersal ability, which plays a crucial role in facilitating the colonization of new habitat, structuring communities, and allowing for speciation through barriers to gene flow, will be considered. The biogeography of hydrothermal vent biotic assemblages globally will be an important topic and factors that influence it will be considered at length. Finally, what is currently known about the evolution of vent fauna will be briefly examined along with a theory which speculates on the origin of life on Earth at hydrothermal vents.

The Complexities and Opportunities of Examining Scale in Ecology – With Application to Grassland Management

Skadi von Reis — Thu, 07 May 2009 09:15:10 PDT

Understanding the way in which biodiversity is created and maintained is the fundamental goal of applied ecology. In order to comprehend how diversity is distributed and isolate the factors contributing to diversity, multiple scales of study must be considered. Studies which base their conclusions on an isolated snapshot of an ecological system find their results challenged by considering both historical and spatial scales. The question of scale: its definition, the relevant scale at which biological processes produce observable patterns, the translation from small to large scales and the theoretical and technological complications scale presents, remain contentious issues in ecology. This review investigates the current definitions of scale, arguments over the importance of various scales, and the use of scalar components in research. Secondly, it looks at how careful consideration of scale gives rise to various limitations and complications of ecological studies. Finally, it addresses the difficulty of scaling up, from local to regional, through ecosystems. The question of scale is then applied to grassland management, a biome both vital to biodiversity and human use, in order to concretize theoretical arguments and provide direction to management. This review is conducted to generate a greater comprehension of scalar applications to future research, the contingency of current conclusions based on scalar limits will, and how this knowledge can be applied to aid management that engages all scales in order to preserve diversity.

Biogeography of Microorganisms Inhabiting Marine Sponges

Suzy C. Szumowski — Thu, 07 May 2009 09:15:09 PDT

Sponge-associated microorganisms are an intriguing system for the consideration of biogeographic patterns due to complications arising from their small size and their symbiotic relationship with sponges. Whether or not microorganisms are capable of exhibiting biogeographic patterns is a topic of heated debate in the literature. Recent studies utilizing new identification techniques have revealed an astonishing amount of diversity and spatiotemporal stability in microorganism communities. Case studies outlined in this paper suggest that some sponge-associated microorganisms represent monophyletic groups that have evolved speciesspecific associations with their hosts. The biogeography of these organisms is receiving increasing attention because they are one of the richest sources of novel bioactive compounds with pharmaceutical applications. Future work in this system should focus on sampling microbial distributions more thoroughly by applying methods with higher phylogenetic resolving power in more diverse habitats.

A Review of Endemic Species in the Eastern Arc Afromontane Region: Importance, Inferences, and Conservation

Carl Skarbek — Thu, 07 May 2009 09:15:08 PDT

The Eastern Arc mountain region has been identified as one of the top 25 biodiversity “hotspots” worldwide, and contains a large proportion of endemic species. The endemic species are invaluable resources. This review paper will explore and discuss the possible theories behind the high rate of endemism. The importance of these endemics to local peoples and to the greater global community has been studied thoroughly, and these results are presented in further detail in this paper. The Eastern Arc is also facing many problems that are threatening the biodiversity and rare endemic species of this region. Human expansion into natural habitat, as well as deforestation and forest fragmentation are among the most pressing issues. The causes and impacts of these issues will be explored and suggestions for the protection and conservation of endemic species and biodiversity will be discussed.

Leishmaniasis: A review of the disease and the debate over the origin and dispersal of the causaitive parasite Leishmania

Molly MacMorris-Adix — Thu, 07 May 2009 09:15:06 PDT

The vector borne disease Leishmaniasis, caused by the Leishmania parasite, is estimated to affect the lives of 12 million people. Manifesting itself into three different clinical forms that center on disfiguring sores and enlargement of several organs, Leishmaniasis is a devastating disease impairing economic productivity and impeding socioeconomic development. The complex life cycle of this parasite, involving a host, vector, and reservoir, has played a major role in defining the dispersal and prevalence of this disease on a global level. The prevalence of Leishmaniasis is highly concentrated due to the close relationship of this parasite and its single vector (the female Phlebotomine sand fly), and the socioeconomic and environmental factors that are beneficial to the sand fly habitat. Yet, there is a wide and varied distribution of Leishmania species. Some species belonging to the subgenera of Leishmania are found in both Old and New Worlds, while others belonging to the subgenera Viannia are found only in the New World. Interest in the origin and dispersal of Leishmania has risen from this disjointed distribution and a need for a complete comprehensive understanding of this parasite in order to determine the best approach in the eradication of this disease. The two main hypotheses from the literature that have become established in this debate are a Palaearctic origin and a Neotropical origin. These hypotheses are presented along with a third hypothesis of an African and Neotropical origin. The conflicts between molecular, entomological, biogeographical, and ecological data, along with insufficient research that have rendered this debate unresolved are also discussed. Complexity of this diseases’ epidemiological cycle demands a comprehensive understanding of the parasite, including its origin and dispersal, to maintain the most effective prevention, treatment, and hopefully eradication.

The Biogeography of Plant Domestication

Alese M. Colehour — Thu, 07 May 2009 09:15:05 PDT

Ranging between 11,000 and 4,000 years ago, several independent origins of agriculture appeared, though scholars disagree on exactly how many. This period, known as the “Neolithic Revolution” or the “Origins of Agriculture,” marks the initial emergence of food production economies. Archaeologists and biologists have worked alongside one another, often using a biogeographical approach, to investigate the origins of useful species, their range expansion, and genetic evolution through analyzing remains found at excavation sites around the world. Plant communities influence patterns in human behaviors and by understanding trends in biogeography we can begin to answer questions such as: Why did plant domestication occur where and when it did? Or, what sorts of evolution and dispersal of domesticates occurred? Understanding patterns of plant domestication is important in understanding distribution patterns in today’s society because it marks the beginning of the most significant developments in human history. Factors such as warmer climates, emergence of seasonality, and physical geography shaped the differences in threatened food security at the turn of the Pleistocene- Holocene. Hunter-gatherer societies turned to crop domestication in order to control their food supplies in a variety of ways. Regional differences in physical geography, soil fertility and local climate variations explain the emergence of different origins around the globe. This paper is a broad review of current and past literature that has shaped our understanding of plant domestication. The research I focus on attempts to answer the question of why agriculture emerged where and when it did, and how plant domesticates subsequently evolved and dispersed. I will discuss the significance of this type of research, review some methodologies, explore incongruities in the field with regard to conceptualizations, outline the biogeography of the independent origins of agriculture, and finally the discuss the human ecology of agricultural societies.