In contrast to their rarity, the commonness of species has historically received surprisingly little explicit attention from ecologists. However, this situation is changing. Here I review the current understanding of the nature of commonness, with particular emphasis on the dynamics and causes of this state, as well as on its ecological and evolutionary implications. Depending on the focal issue, common species can variously have lower, greater, or similar per capita influences compared with rare ones. Importantly, however, these influences almost invariably remain strong because of the high numbers of individuals and local occurrences in taxonomic assemblages contributed by the relatively few species that are common. The importance of these species highlights the significance of deepening concerns over the declines of many common species and the vital need for a balanced approach to maintaining their commonness while also addressing the more familiar conservation issue of preventing the loss of rare species.

Park managers realized more than 130 years ago that protected areas are often subsets of larger ecosystems and are vulnerable to change in the unprotected portions of the ecosystem. We illustrate the need to delineate protected area—centered ecosystems (PACEs) by using comprehensive scientific methods to map and analyze land-use change within PACEs around 13 US national park units. The resulting PACEs were on average 6.7 times larger than the parks in upper watersheds and 44.6 times larger than those in middle watersheds. The sizes of these PACEs clearly emphasized the long-term reliance of park biodiversity on surrounding landscapes. PACEs in the eastern United States were dominated by private lands with high rates of land development, suggesting that they offer the greatest challenge for management. Delineating PACEs more broadly will facilitate monitoring, condition assessment, and conservation of the large number of protected areas worldwide that are being degraded by human activities in the areas that surround them.

Killifish, grass shrimp, fiddler crabs, blue crabs, and young bluefish in contaminated estuaries differ ecologically from reference populations in relatively uncontaminated environments. All five of these species show reduced activity and feeding, but only fishes show reduced growth. In these areas, killifish are poor predators, eat much detritus, have poor predator avoidance, and are smaller and less abundant. Bluefish have reduced rates of feeding and growth. Both killifish and bluefish have altered thyroid glands and neurotransmitters, which may underlie behavioral changes. Shrimp in contaminated environments show unchanged levels of predator avoidance; compensatory energetic partitioning favors growth and reproduction despite reduced feeding. With less predation pressure, shrimp are larger and more numerous. Fiddler crabs tend to spend more time in burrows and experience reduced predation. With ample food, metal depuration through molting, and reduced population size, they grow larger. In contaminated estuaries, we've found that juvenile blue crabs are less likely to be eaten by adults; adults are impaired in prey capture but are larger, despite eating much detritus and algae. Release from top-down effects from humans—as a result of a fishery advisory—may allow crabs to live longer. It appears that differences in physiology and trophic interactions modify the effects of reduced feeding on the different species.

Ecologists at primarily undergraduate institutions (PUIs) are well positioned to form collaborative networks and make transformative contributions to the study and teaching of ecology. The spatial and temporal complexity of ecological phenomena rewards a collaborative research approach. A network of PUI ecologists can incorporate closely supervised data collection into undergraduate courses, thereby generating data across spatial gradients to answer crucial questions. These data can offer unprecedented insight into fine- and large-scale spatial processes for publications, resource management, and policy decisions. Undergraduate students benefit from the collaborative research experience as they gain experiential learning in team building, project design, implementation, data collection, and analysis. With appropriate funding, collaborative networks make excellent use of the intellectual and experiential capital of PUI faculty for the benefit of science, pedagogy, and society.

Fourteen marine species in the Gulf of Mexico are protected by the US Endangered Species Act, the Marine Mammal Protection Act, and the Migratory Bird Treaty Act. As the British Petroleum oil spill recovery and remediation proceed, species internationally recognized as having an elevated risk of extinction should also receive priority for protection and restoration efforts, whether or not they have specific legal protection. Forty additional marine species—unprotected by any federal laws—occur in the Gulf and are listed as threatened on the International Union for Conservation of Nature's (IUCN) Red List. The Red List assessment process scientifically evaluates species' global status and is therefore a key mechanism for transboundary impact assessments and for coordinating international conservation action. Environmental impact assessments conducted for future offshore oil and gas development should incorporate available data on globally threatened species, including species on the IUCN Red List. This consideration is particularly important because US Natural Resource Damage Assessments may not account for injury to highly migratory, globally threatened species.

Artificial ecosystem selection is an experimental technique that treats microbial communities as though they were discrete units by applying selection on community-level properties. Highly diverse microbial communities associated with humans and other organisms can have significant impacts on the health of the host. It is difficult to find correlations between microbial community composition and community-associated diseases, in part because it may be impossible to define a universal and robust species concept for microbes. Microbial communities are composed of potentially thousands of unique populations that evolved in intimate contact, so it is appropriate in many situations to view the community as the unit of analysis. This perspective is supported by recent discoveries using metagenomics and pangenomics. Artificial ecosystem selection experiments can be costly, but they bring the logical rigor of biological model systems to the emerging field of microbial community analysis.