Succession in the aquatic Sarracenia purpurea community: deterministic or driven by contingency?

Abstract

The development of a community through time, or succession, is generally described as the orderly replacement of species until a deterministic, stable endpoint is reached. However, stochastic factors, coupled with intrinsic biotic factors, such as herbivory or predation, can cause communities within the same habitat to become highly dissimilar in composition. Much research on the succession of terrestrial systems has been conducted, but factors influencing the succession of a terrestrial system may not apply to aquatic systems. To determine whether succession in an aquatic system is deterministic or dominated by contingency of stochastic factors, and the role that higher trophic level interactions and resources have in shaping successional patterns, I followed community development and dynamics of the intermediate and bottom trophic level (protozoans and bacteria) in the model Sarracenia purpurea pitcher plant system throughout an entire growing season. By comparing these dynamics across pitcher plant leaves within the same bog, I was able to determine whether there is a predictable pattern for community assembly in this aquatic community. The results from this study suggest that rather than a sequential replacement of early colonizers with more competitive species through time, competitively superior species establish in newly formed communities simultaneously with less competitive species, which coexist throughout the growing season. Community assembly in this system can also be altered by stochastic events. Resources and predators had a variable effect on the patterns of community change observed during succession. Patterns of community assembly were also dependent on the trophic level examined but, for the bottom trophic level, not on the sampling method used.

The Bacterial Composition within the Sarracenia purpurea Model System: Local Scale Differences and the Relationship with the Other Members of the Food Web

“…Alternatively, the filter occurs later in community development for bacteria and interactions with the higher trophic level as well as resource input and extrinsic factors may shape the bacterial community in some aspects through time. Within the NY study site, this pattern is supported by findings in Gray [32], in which communities converge to be more similar in bacterial composition at the end of the season and to contain a different composition when compared to communities at the beginning of the season.…”

Top predators affect the composition of naive protist communities, but only in their early-successional stage

“…The aquatic communities that were collected from the 4-week-old leaves were designated as "late-succession communities" and the aquatic communities that were from 2-week-old leaves were designated as "early-succession communities". A 1-month duration is a reasonable interval for this community to reach late-succession because the community consists of bacteria and protists, which have fast generation times (Gray 2012). Note that early-and late-succession communities from Québec already experienced W. smithii predation at the time of sampling [W. smithii lay their eggs immediately after pitcher opening (Smith 1902)].…”

Temperature and trophic structure are driving microbial productivity along a biogeographical gradient

“…Bacterial density was then standardized across sites by adjusting the volume of the communities with autoclaved deionized water, resulting in 1.09 × 10 7 bacteria per ml for each origin. This technique is standard for research conducted on the Sarracenia system, as it has been shown that the members of the food web are able to easily survive and maintain normal interactions, even when placed directly into deionized water (Kneitel and Miller , Hoekman , Gray , Kadowaki et al , Kneitel , Zander et al ). As a control, an equal volume of water from each of the five sites was also pooled to make the ‘mixed origin’ community.…”

“…The experiment was conducted over 6 d, which is equivalent to approximately 18 to 24 generations of protozoans (Lüftenegger et al ) and 48 generations of bacteria (Gray et al ). The experiment ended when the bacteria and protozoans were expected to reach their carrying capacities in this system (Gray , Kadowaki et al ). The fast generation time of microbial systems thus allows experiments to be conducted over a short amount of time, while producing results equivalent to longer‐term experiments on larger organisms (Srivastava et al ).…”