The vast majority of organisms are well adapted to the environments in which they live. Living conditions, however, are not stationary. As a consequence, the interaction of environmental change and natural selection has caused the evolution of new morphologies throughout geological time. Several physical, chemical and biological factors have controlled the morphological developments both in the organisms and the communities. In this lecture we will take a look at one of the most important ones, predation. Predators have evolved a range of methods to catch, suppress, or exploit their prey, for instance sharp teeth, fast running speed, and camouflage. On the other hand, prey have evolved a variety of predator defence mechanisms to allow them to escape their predators or reduce their appeal as prey, for instance fast speed, chemical and physical defences and camouflage. In ecology, predation is a mechanism of population control. Thus, when the number of predators is scarce, the number of preys should rise. When this happens, the predators would be able to reproduce more and possibly change their hunting habits. As the number of predators rises, the number of preys decline. This results in food scarcity for predators that can eventually lead to the death of many predators. Defined in a general way, predation is a category of ecological interactions in which one species benefits (that is the predator) while the second species – that is the prey - is harmed. In 2002 Bengtson defined predation as an ecological interaction between two organisms in which the predator kills the prey. This definition includes two main forms of predation: killing by eating, which is also called macrophagous predation, and killing by grazing. A macrophagous predator is one that kills and eats another organism, and causes the preys certain death. In contrast, grazing predators are organisms, which in the end kill their prey, but it may take some time for them to do so. Two very common methods to kill the prey are drilling and crushing. Carnivorous, naticid gastropods were, and still are, very important members of the first group, while, for instance, crabs, lobsters, sharks and plesiosaurs crush their prey. If an adaption in a predator lineage changes the selection pressure on the prey lineage, a counter-adaption may be developed in the prey lineage. If this pressure also occurs the opposite way, an unstable evolutionary arms race situation may be the result. Predation affects the distribution and abundance of organisms and, as a result, the diversity and composition of communities. Because it has been suggested that predation is an important driving force in evolution, the role of predation and predator-prey interactions have been debated intensively during the past few decades. One of the disputed themes has been the role of two processes directly related to predation – coevolution and escalation. Coevolution involves reciprocal adaption, while escalation involves adaption to enemies. Dietl & Kelley in 2002 explained the two related mechanisms in this way: In coevolution, the claws of the predator get stronger and the prey’s shell becomes thicker in reciprocal response. In escalation, increased defence in the prey is a response to the stronger claws of its predator, but the increased claw strength of the predator is a response to agents other than the prey. In the latter situation predator and prey taxa did not coevolve. Instead each adapted in response to its own enemies. Since predators impose a selective force on their prey, while prey reciprocally impose selective pressures on their predators, it may be expected that coevolution between predators and prey is common. As an example, predation by foxes should result in faster rabbits which, in turn, should give rise to faster foxes, which in turn should cause faster rabbits, and so on. Such arms races between predators and prey have strongly influenced the traits of many organisms. Let us take a closer look at the Mesozoic arms race in marine environments. The recovery period after the end-Permian mass-extinction was much longer than for any other extinction event and indicates that the ecosystems were completely broken down. It took almost 100 Ma for family diversity to reach pre-extinction levels, and it is clear that the Permo-Triassic extinction crisis formed a major setback for all marine communities. Also many Palaeozoic predators were eliminated, including certain groups of gastropods, goniatitic ammonoids, and many early lineages of sharks. In contrast, other active predatory groups survived the extinction event, including the hybodontid sharks and the root-stocks of Mesozoic crustaceans and ammonoids. Predators thus seem to have rebounded rather quickly, and by the Middle Triassic many new predators had appeared, e.g. decapods, shell-crushing sharks and bony fish. Newly appeared carnivorous, marine reptiles from the Triassic include for example durophagous (that is shell-biting) placodonts and different “reptile” groups such as ichtyosaurs and the first plesiosaurs. The subsequent Jurassic and Early Cretaceous periods gave rise to continued diversifications within a broad range of predators, e.g. ammonites (cephalopods) and the rapid-swimming ancestors of the living 10-armed coleoid cephalopods and malacostracan crustaceans with crushing chelae. Malacostraca is the largest crustacean class and includes e.g. crabs, lobsters, shrimps and krill. Fish (especially sharks), ichthyosaurs and up to 15 m long plesiosaurs are regarded the principal marine vertebrate predators. The Cretaceous was characterised by a substantial reorganisation of marine predators including the occurrence of neogastropods; a diverse cephalopod fauna dominated by carnivorous, nektonic ammonites and coleoids and crustaceans including stomatopods. Among the vertebrates, sharks, sea turtles, and the marine reptiles such as plesiosaurs and mosasaurs, radiated strongly during the Cretaceous. As noted above, significant new configurations in the shallow marine benthic communities were introduced during the middle and late Mesozoic. In 1977 Vermeij named this the Mesozoic marine revolution. The result was the initiation of more intensive grazing and a clearly more diverse durophagous predator fauna including animals such as carnivorous gastropods, decapod crustaceans and different fish lineages. Many new animal lineages with the ability to break shells appeared such as sharks, rays, lobsters, crabs and birds. A response to these changes was that bioturbation and infaunal life modes (that means underneath the sea floor) increased, and that crinoids and brachiopods disappeared from shallow-water habitats. Instead new deeper-water communities appeared during this period. Additionally, it has been shown that the prey shell robustness and frequencies of shell repairs increased. It was suggested by Vermeij in 1977 that the Mesozoic marine revolution might represent the intensification of species sorting or selection by physical or palaeogeographical conditions of the Mesozoic, which permitted synchronous changes in different groups of organisms. As an example, pleasant living conditions with a mild climate, may have given rise to the expansion of predators as well as prey with predation-resistant morphologies. It is still heavily disputed if the morphological changes were driven by coevolution or escalation or possibly both, but many researchers - including Vermeij 1977 and Liz Harper in 2006 - regard escalation as the probably most important agent of natural selection because predators are more likely to respond evolutionary on their own enemies than to antipredatory adaptions of the prey. It is very difficult, however, to distinguish between the two from the fossil record. The biological evolutionary changes forced by, for instance, the predator-prey interactions that occurred during the Mesozoic marine revolution, led to the successful evolution and diversification of the marine Modern Evolutionary Fauna, which is still dominating the marine environments today.
