Immigration and zooplankton community responses to nutrient enrichment: a mesocosm experiment

Abstract

Dispersal can be an important determinant of local diversity and species composition, but evidence for effects of the regional species pool on local zooplankton communities has been mixed. Theory and experiments suggest that immigration will be necessary for maintenance of community diversity and functioning during periods of environmental change; conversely, fluctuating resource levels may increase the likelihood of invasion success. We conducted a factorial-design mesocosm experiment to test the effects of a nutrient pulse and weekly immigration from other lakes on the diversity and composition of a pelagic zooplankton community. Contrary to expectations, there were no interactive effects of nutrient enrichment and immigration on any measure of diversity, and the initial shift in community composition in response to the nutrient pulse did not depend on the introduction of new species or genotypes from more productive lakes. Although immigration increased species richness in enclosures, success of most colonising species was poor. However, the dispersal treatment appears to have enabled a stronger predator response to increased herbivore numbers in nutrient-pulsed enclosures, leading to an eventual decline in the abundance of some herbivorous species in response to immigration. We conclude that community invasibility was not influenced by productivity, and that dispersal limitation did not strongly constrain the response of the zooplankton community to our applied disturbance. This indicates an unexpected resistance to change in species composition and diversity in spite of disturbance, and suggests that, in our study system, changes in the abundance of resident species are more important than introductions of new species in the community response to short-term environmental change.

Timing is everything: priority effects alter community invasibility after disturbance

“…This supports the results of many aquatic and terrestrial experiments where undisturbed communities resist the establishment of dispersers (Shurin ; Fargione et al. ; Forrest and Arnott ; Strecker and Arnott ).…”

“…Under control conditions, invasibility was low, and disperser species rarely established, or remained at low relative abundance. This supports the results of many aquatic and terrestrial experiments where undisturbed communities resist the establishment of dispersers (Shurin 2000;Fargione et al 2003;Forrest and Arnott 2006;Strecker and Arnott 2010).…”

“…). Experiments that have manipulated abiotic and/or biotic variables and controlled propagule pressure have shown that disturbance increases invasibility in terrestrial systems (e.g., Burke and Grime ; Davis and Pelsor ), freshwater systems (Strecker and Arnott but see Forrest and Arnott ), and marine systems (e.g., Clark and Johnston ).…”

“…The amount of unused resources can increase in two ways: resource availability can increase or resource use by the resident community can decrease (Davis et al 2000). Experiments that have manipulated abiotic and/or biotic variables and controlled propagule pressure have shown that disturbance increases invasibility in terrestrial systems (e.g., Burke and Grime 1996;Davis and Pelsor 2001), freshwater systems (Strecker and Arnott 2010 but see Forrest and Arnott 2006), and marine systems (e.g., Clark and Johnston 2009).…”

Can dispersal buffer against salinity‐driven zooplankton community change in Great Plains' lakes?

“…For example, one species of Daphnia could be replaced by another, or a salinity-tolerant phenotype of a Daphnia species could replace a salinity-intolerant member of the same species. Manipulative experiments also provide some support for the idea that dispersal can act to buffer against community change in the case of small increases in salinity (Symons & Arnott, 2013;Thompson & Shurin, 2012) or when zooplankton are exposed to other stressors such as nutrient enrichment (Forrest & Arnott, 2006), acidification (Steiner et al, 2011) and introduced predators (Howeth & Leibold 2010). The likelihood that dispersal could act to counter salinity-driven changes in this manner depends on two assumptions: (1) that dispersal occurs at a temporal and spatial scale that is significant enough to compensate for losses; and (2) that variation in salinity tolerance among populations and species occurs among lakes with varying salinity levels.…”