Toward a trophic theory of species diversity

Behavioral interference between species, such as territorial aggression, courtship, and mating, is widespread in animals. While aggressive and reproductive forms of interspecific interference have generally been studied separately, their many parallels and connections warrant a unified conceptual approach. Substantial evidence exists that aggressive and reproductive interference have pervasive effects on species coexistence, range limits, and evolutionary processes, including divergent and convergent forms of character displacement. Alien species invasions and climate change-induced range shifts result in novel interspecific interactions, heightening the importance of predicting the consequences of species interactions, and behavioral interference is a fundamental but neglected part of the equation. Here, we outline priorities for further theoretical and empirical research on the ecological and evolutionary consequences of behavioral interference. Interspecific Aggression and Reproductive InterferenceFew subjects in animal behavior have attracted more attention than aggression and sex, yet research tends to stop at species boundaries even when the behaviors themselves do not. Aggressive and sexual interactions between species are surprisingly common and share many parallels in their causes and ecological and evolutionary effects [1][2][3][4][5][6]. Both types of behavioral interference (Box 1) have been hypothesized to: (i) arise as a byproduct of intraspecific interactions (Box 2); (ii) cause local extinction as well as temporal and spatial habitat partitioning; (iii) prevent species from coexisting that otherwise would be expected to coexist; (iv) enable coexistence between species that otherwise would not be expected to coexist; (v) promote or prevent species range shifts and the spread of invasive species; (vi) cause sympatric species to diverge or converge through character displacement processes; (vii) cause populations within a species to diverge from each other due to character displacement in areas of sympatry; and (viii) contribute to reproductive isolation and speciation ( Figure 1).Despite their connections, aggressive interference and reproductive interference (see Glossary) have largely been studied by different researchers in relation to different theoretical frameworks [2,4,7] and in different study systems [3], even though many closely related species interfere with each other in both ways (see Table S1 in [8]). We do not believe that these two categories of interspecific interactions should be synonymized, because this would obscure important differences between them. Instead, we propose that their similarities and interrelationships merit a common conceptual framework, which we introduce here ( Figure 1). TrendsAggressive and reproductive forms of behavioral interference between species are widespread in animals and share many parallels in their underlying causes and their ecological and evolutionary effects.Behavioral interference can determine whether species coexist and, thus, affects speci...

Recent discoveries of multiple middle Pliocene hominins have raised the possibility that early hominins were as speciose as later hominins. However, debates continue to arise around the validity of most of these new taxa, largely based on poor preservation of holotype specimens, small sample size, or the lack of evidence for ecological diversity. A closer look at the currently available fossil evidence from Ethiopia, Kenya, and Chad indicate that Australopithecus afarensis was not the only hominin species during the middle Pliocene, and that there were other species clearly distinguishable from it by their locomotor adaptation and diet. Although there is no doubt that the presence of multiple species during the middle Pliocene opens new windows into our evolutionary past, it also complicates our understanding of early hominin taxonomy and phylogenetic relationships.If one looks back over the controversies of human evolution, they have one element in common: new discoveries, theories, methods came along which no one in the controversy anticipated. The "facts" changed, and consequently people were not right or wrong in any simple way.S. L. Washburn and R. L. Ciochon, 1974 (1) New fossil discoveries and analytical methods that have proliferated during the last few decades have fundamentally changed how we study and interpret hominin fossils and understand human evolution. The discovery and subsequent naming of Australopithecus afarensis in the late 1970s was one of the major milestones in paleoanthropology (2). Its discovery not only pushed the record of hominins to earlier than 3 million years ago (Ma) (2), but also demonstrated the antiquity of human-like bipedality (3). However, the taxonomic homogeneity of the Au. afarensis hypodigm has been questioned since its naming (4-7), even though the Hadar fossil sample appears to be no more variable than other living ape species (8-11). A consensus emerged during the 1980s in which Au. afarensis, dated to between 3.7 and 2.9 Ma, was considered to be the sole early hominin species older than 3 Ma, largely supported by the lack of fossil evidence to indicate otherwise.When Australopithecus bahrelghazali was named in 1995 based on an approximately 3.5-Ma partial mandible from Chad (12), it was quickly dismissed as a geographic variant of Au. afarensis (13-15). The initial descriptions of Ardipithecus ramidus (16) and Australopithecus anamensis (17), followed by the naming of even earlier hominin species, such as Orrorin tugenensis (18), Ardipithecus kadabba (19,20), and Sahelanthropus tchadensis (21), extended the antiquity of our lineage as far back as >6 Ma. These early hominins initially appeared to show no temporal or spatial overlap, and hence reinforced the idea that the early phases of hominin evolution were characterized by phenetic continuity and phyletic gradualism, with only one hominin species existing in a region at any given time >3 Ma (e.g., ref. 22; see discussions below).The discovery of the Burtele partial foot from Ethiopia (23), the naming of Kenyan...

The increased frequency of publications concerning trophic ecology of coral reefs suggests a degree of interest in the role species and functional groups play in energy flow within these systems. Coral reef ecosystems are particularly complex, however, and assignment of trophic positions requires precise knowledge of mechanisms driving food webs and population dynamics. Competent analytical tools and empirical analysis are integral to defining ecosystem processes and avoiding misinterpretation of results. Here we examine the contribution of trophodynamics to informing ecological roles and understanding of coral reef ecology. Applied trophic studies of coral reefs were used to identify recent trends in methodology and analysis. Although research is increasing, clear definitions and scaling of studies is lacking. Trophodynamic studies will require more precise spatial and temporal data collection and analysis using multiple methods to fully explore the complex interactions within coral reef ecosystems.