Complex Species Interactions and the Dynamics of Ecological Systems: Long-Term Experiments

Abstract

Studies that combine experimental manipulations with long-term data collection reveal elaborate interactions among species that affect the structure and dynamics of ecosystems. Research programs in U.S. desert shrubland and pinyon-juniper woodland have shown that (i) complex dynamics of species populations reflect interactions with other organisms and fluctuating climate; (ii) genotype x environment interactions affect responses of species to environmental change; (iii) herbivore-resistance traits of dominant plant species and impacts of "keystone" animal species cascade through the system to affect many organisms and ecosystem processes; and (iv) some environmental perturbations can cause wholesale reorganization of ecosystems because they exceed the ecological tolerances of dominant or keystone species, whereas other changes may be buffered because of the compensatory dynamics of complementary species.

Regional vegetation die-off in response to global-change-type drought

“…Our results highlight how drought-induced die-off can span across the range of a vegetation type and challenges the current paradigm for climate-induced vegetation dynamics, which focuses largely on changes at the margins of a species' range and the ecotone boundaries within that range (1,5,6). Additionally, if temperatures continue to warm, vegetation die-off in response to future drought may be further amplified (5,8,9,12). This recent drought episode in southwestern North America may be a harbinger of future global-change-type drought throughout much of North America and elsewhere, in which increased temperature in concert with multidecadal drought patterns associated with oceanic sea surface oscillations can drive extensive and rapid changes in vegetation and associated land surface properties.…”

“…The rapid, extensive regional changes in vegetation cover through tree die-off that we have quantified for southwestern North America have a number of important, interrelated ecological implications (12,24), including potentially large changes in carbon stores and dynamics, of concern for carbon-related polices and management (9). Other interrelated implications include large changes in near-ground solar radiation (25), runoff Aerial survey map of piñ on-juniper woodlands, delineating areas that experienced noticeable levels of tree mortality (including larger, older trees), conducted by the U.S. Forest Service (19) in four study areas throughout the region, corroborates the NDVI and aerial survey maps and documents standlevel estimates of mortality that range from 40% to 80% of nonseedling trees.…”

“…We evaluated the impacts of the recent drought on regional-scale mortality of piñon pine (Pinus edulis), which is sensitive to climate variation and dominates piñon-juniper woodlands, one of the most extensive vegetation types in the western North America (10)(11)(12). Specifically, we evaluated the impacts of the recent drought on regional-scale mortality in the context of the potential impacts of global-change-type drought, and (i) demonstrated that the recent drought is not as dry as the previous drought but is warmer in numerous respects, thereby providing a case study for globalchange-type drought; (ii) quantified site-specific conditions in soil water content and local vegetation response (percentage of tree mortality, and a remotely sensed vegetation index related to photosynthetic activity and associated greenness, Normalized Difference Vegetation Index, NDVI) to precipitation and temperature dynamics; and (iii) estimated and verified regional-scale stress and mortality responses in vegetation to drought by using weekly NDVI data back to 1989 and supplemental aerial surveys and field inventories.…”

Community ecology in a changing environment: Perspectives from the Quaternary

“…Comparative studies of secondary communities (mycorrhizae, invertebrates, vertebrates), using antiquity of the plant community as an independent variable, can provide insights into processes of community development and evolution (122). Age may be one among many differences among sites, but other properties (e.g., physical environment, climate history, genetics) can be controlled in study design.…”

Genetic variation in response to an indirect ecological effect

“…In natural food webs consisting of many interconnected food chains, there exists the possibility of numerous IEEs. These can be a significant cause of phenotypic variation, are sometimes stronger than direct effects (Brown et al 2001), and may even act antagonistically to direct effects thereby leading to unexpected experimental results (Wootton 1994). As Miller & Travis (1996) highlight, given that IEEs have significant community effects they could also be an important selective force affecting adaptive evolution of the species involved.…”