PARENT SESSION
Symposium 22: Expanding Scales, Expanding Perspectives: New Insights into Marine Ecosystem Dynamics
Organized by: P Raimondi and B Menge
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Oglethorpe Auditorium.
Temporal and spatial variation in positive and negative interactions among salt marsh plants: The role of climate and community.
Pennings, Steven*,1, Bertness, Mark2, Ewanchuk, Patrick2, Selig, Elizabeth2, Houser, Letise2, 1 Department of Biology and Biochemistry, Houston, TX, USA2 Department of Ecology and Evolutionary Biology, Providence, RI, USA
ABSTRACT- A pressing problem for ecologists is determining whether our understanding of communities, often developed from work at fine scales, can explain processes across broader scales. Here, we explore whether models of positive interactions developed in southern New England can be applied at geographic scales. Salt marsh plants may interact positively by ameliorating harsh physical conditions such as salinity stress. Because salinities are higher in low- versus high-latitude marshes, and in dry versus wet years, we tested the hypotheses that positive interactions would be increasingly important at low latitudes and in dry years. We conducted parallel experiments in Maine, Rhode Island, Georgia and Alabama. Multiple species of salt marsh plants were transplanted into control plots or plots with neighboring vegetation removed, in multiple marsh zones, at two sites/state. The experiments were repeated over 3-4 years. Our hypotheses were supported at the regional scale. Within New England, positive interactions were rare in Maine but common in Rhode Island, and were more important in dry than wet years. At the geographic scale, our hypotheses were not supported. Positive interactions were not more important in southern (Georgia, Alabama) than northern (Maine, Rhode Island) sites. Rather, most interactions in southern sites were competitive. The most likely explanation for our results is that northern floras were dominated by salt-sensitive species that were likely to be facilitated by neighbors, whereas southern floras were dominated by salt-tolerant species that were unlikely to benefit substantially from neighbor-amelioration of salinities. Intraspecific variation in salt-tolerance may also have contributed to a reduced occurrence of facilitation at southern sites. These results illustrate the difficulties inherent in extrapolating results from even well understood systems to different geographic locations or scales. Intraspecific adaptations and community composition will often vary geographically, complicating our efforts to construct geographically robust generalities about community structure and processes.
Key words: latitude, salt marsh, competition, facilitation