We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

The increasing availability of phylogenetic data, computing power and informatics tools has facilitated a rapid expansion of studies that apply phylogenetic data and methods to community ecology. Several key areas are reviewed in which phylogenetic information helps to resolve long-standing controversies in community ecology, challenges previous assumptions, and opens new areas of investigation. In particular, studies in phylogenetic community ecology have helped to reveal the multitude of processes driving community assembly and have demonstrated the importance of evolution in the assembly process. Phylogenetic approaches have also increased understanding of the consequences of community interactions for speciation, adaptation and extinction. Finally, phylogenetic community structure and composition holds promise for predicting ecosystem processes and impacts of global change. Major challenges to advancing these areas remain. In particular, determining the extent to which ecologically relevant traits are phylogenetically conserved or convergent, and over what temporal scale, is critical to understanding the causes of community phylogenetic structure and its evolutionary and ecosystem consequences. Harnessing phylogenetic information to understand and forecast changes in diversity and dynamics of communities is a critical step in managing and restoring the Earths biota in a time of rapid global change.

https://projects.au.dk/fileadmin/projects/circe/2009_Cavender_et_al_01.pdf

The merging of community ecology and phylogenetic biology

Half of all insect species are dependent on living plant tissues, consuming about 10% of plant annual production in natural habitats and an even greater percentage in agricultural systems, despite sophisticated control measures. Plants are generally remarkably well-protected against insect attack, with the result that most insects are highly specialized feeders. The mechanisms underlying plant resistance to invading herbivores on the one side, and insect food specialization on the other, are the main subjects of this book. For insects these include food-plant selection and the complex sensory processes involved, with their implications for learning and nutritional physiology, as well as the endocrinological spects of life cycle synchronization with host plant phenology. In the case of plants exposed to insect herbivores, they include the activation of defence systems in order to minimize damage, as well as the emission of chemical signals that may attract natural enemies of the invading herbivores and maybe exploited by neighbouring plants that mount defences as well.

Insect-plant biology

A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification. This hypothesis is supported by observations that temperate taxa are often younger than, and nested within, tropical taxa, and that diversity is positively correlated with the age and area of geographical regions. The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation (caused by increased opportunities for the evolution of reproductive isolation, or faster molecular evolution, or the increased importance of biotic interactions), or due to lower extinction rates. There is phylogenetic evidence for higher rates of diversification in tropical clades, and palaeontological data demonstrate higher rates of origination for tropical taxa, but mixed evidence for latitudinal differences in extinction rates. Studies of latitudinal variation in incipient speciation also suggest faster speciation in the tropics. Distinguishing the roles of history, speciation and extinction in the origin of the latitudinal gradient represents a major challenge to future research.

/pdf/evolution-and-the-latitudinal-diversity-gradient-speciation-1da5mtz6ph.pdf

Evolution and the latitudinal diversity gradient: speciation, extinction and biogeography

The Cerrado is one of the world's biodiversity hotspots. In the last 35 years, more than 50% of its approximately 2 million km 2 has been transformed into pasture and agricultural lands planted in cash crops. The Cerrado has the richest flora among the world's savannas (>7000 species) and high levels of endemism. Species richness of birds, fishes, reptiles, amphibians, and insects is equally high, whereas mammal diversity is relatively low. Deforestation rates have been higher in the Cerrado than in the Amazon rainforest, and conservation efforts have been modest: only 2.2% of its area is under legal protection. Numerous animal and plant species are threatened with extinction, and an estimated 20% of threatened and endemic species do not occur in protected areas. Soil erosion, the degradation of the diverse Cerrado vegetation formations, and the spread of exotic grasses are widespread and major threats. The use of fire for clearing land and to encourage new growth for pasture has also caused damage, even though the Cerrado is a fire-adapted ecosystem. Ecosystem experiments and modeling show that change in land cover is altering the hydrology and affecting carbon stocks and fluxes. Cerrado agriculture is lucrative, and agricultural expansion is expected to continue, requiring improvements in and extension of the transportation infrastructure, which will affect not only the Cerrado but also the Amazon forest. Large-scale landscape modification and threats to numerous species have led to renewed interest from various sectors in promoting the conservation of the Cerrado, particularly through strengthening and enlarging the system of protected areas and improving farming practices and thus the livelihoods of local communities.

/pdf/conservation-of-the-brazilian-cerrado-514udh8nt4.pdf

Conservation of the Brazilian Cerrado

16. Interactions Among Cerrado Plants and Their Herbivores: Unique or Typical?

Este trabajo se realizo desde 1991 a 1995 en cuatro areas de cerrado sensu stricto en Brasilia, DF, Brasil. El clima de la region es estacional, con las estaciones seca y lluviosa bien marcadas. Nueve especies de plantas hospederas (tres generos y tres familias) fueron examinadas en 10 800 censos desde 1993 a 1995 y en 15% de ellas se encontraron larvas. Se obtuvieron los adultos de 247 especies de lepidopteros (32 familias). La proporcion de plantas con larvas aumento rapidamente a partir del 15 de abril, permaneciendo alta hasta julio, estacion de seca y fue menor al comenzar la estacion lluviosa. La duracion media del periodo de pupa varia durante el ano (multivoltinas). La baja densidad de larvas al inicio de las lluvias podria deberse al estres hidrico acumulado durante la estacion seca; la defensa quimica y fisica de las hojas nuevas; la demora en la emergencia de los adultos y la actividad de depredadores y parasitoides. Probablemente el espacio libre de enemigos durante los tres primeros meses de la epoca seca favorece la abundancia de larvas en el campo.

/pdf/caterpillar-seasonality-in-a-central-brazilian-cerrado-2ldjpqppif.pdf

Caterpillar seasonality in a central Brazilian cerrado

The cerrado biome is rich in caterpillar species although the general biology and ecology of most tropical species remains unknown. Three host plant genera (Byrsonima, Erythroxylum and Qualea) were examined for caterpillars in four cerrado sensu stricto areas near Brasi´lia (DF, Brazil), from 1991 to 1995. Altogether, more than 16000 host plants were sampled and less than 20% of them possessed caterpillars. All the caterpillars found were reared under laboratory conditions. We successfully reared 137 species of 24 lepidopteran families. The average number of caterpillar species per host species was 28.3. The faunal similarity among plant genera, as well as among study sites, was low, and not related to the distances between them. The low proportion of host plants with caterpillars and the high incidence of rare species appears to be a general pattern for the cerrado. A large proportion (74%) of the caterpillar species occurred on only one host plant family. The most frequent species were either specialists (restricted to one host plant genus) or generalists. We provide a brief outline of some taxonomic problems, some observations on general biology, and temporal and local patterns of some specific caterpillars species. The methodology used, which included weekly data collection, in restricted study areas of the same habitat, with the same sampling method for recording the caterpillar species on the same host plant species, can be used as a tool to explore biodiversity and to discuss some aspects of the conservation of cerrado insects.

Lepidopteran caterpillar fauna of cerrado host plants

Leaf traits and herbivory on deciduous and evergreen trees in a tropical dry forest

Several studies have demonstrated that the diversification of the agroecosystem may reduce insect pest infestation using the strategy of companion planting. We studied the effect of the presence of coriander and Gallant soldier as companion plants in the tomato crop under organic and conventional management on abundance of the tomato pests and predators. The experiment was carried out under field conditions, at Distrito Federal, Brazil, from July to October, 2004. The experimental design was of randomized blocks with three replicates in a 3 x 2 factorial arrangement [Three crop diversification levels: tomato in monoculture, tomato intercropped with coriander, and tomato intercropped with coriander and Gallant soldier; and two cropping systems: organic and conventional]. Each plot had 80 plants of the tomato and the pest-insects and predaceous arthropods were collected every week in five tomato plants/plot. Tuta absoluta (Meyr.) was the commonest pest species in both cropping systems. The tomato intercropped with coriander and Gallant soldier in organic cropping system had lower abundance and higher diversity of pests, and higher abundance and diversity of predaceous arthropods, mainly at 80 days after the tomato transplanting, coinciding with the population peak of T. absoluta (eggs and adults). The more abundant predators were spiders, lady beetles and ants. The spiders were abundant and uniformly distributed in both systems. The lady beetles appeared lately in the organic system, at the flowering season of the coriander. The ants were more abundant in the conventional systems.

/pdf/effect-of-plant-diversification-on-abundance-of-south-2wzml59qzf.pdf

Helena C. Morais

Papers

16. Interactions Among Cerrado Plants and Their Herbivores: Unique or Typical?

Caterpillar seasonality in a central Brazilian cerrado

Lepidopteran caterpillar fauna of cerrado host plants

Leaf traits and herbivory on deciduous and evergreen trees in a tropical dry forest

Effect of plant diversification on abundance of South American tomato pinworm and predators in two cropping systems