Abstract
By associating closely with others to form a group, an animal can benefit from a number of advantages including reduced risk of predation, amelioration of environmental conditions, and increased reproductive success, but at the price of reduced resources. Although made up of individual members, an aggregation often displays novel effects that do not manifest at the level of the individual organism. Here we show that very simple behaviour in intertidal mussels shows new effects in dense aggregations but not in isolated individuals. Perna perna and Mytilus galloprovincialis are gaping (periodic valve movement during emersion) and non-gaping mussels respectively. P. perna gaping behaviour had no effect on body temperatures of isolated individuals, while it led to increased humidity and decreased temperatures in dense groups (beds). Gaping resulted in cooler body temperatures for P. perna than M. galloprovincialis when in aggregations, while solitary individuals exhibited the highest temperatures. Gradients of increasing body temperature were detected from the center to edges of beds, but M. galloprovincialis at the edge had the same temperature as isolated individuals. Furthermore, a field study showed that during periods of severe heat stress, mortality rates of mussels within beds of the gaping P. perna were lower than those of isolated individuals or within beds of M. galloprovincialis, highlighting the determinant role of gaping on fitness and group functioning. We demonstrate that new effects of very simple individual behaviour lead to amelioration of abiotic conditions at the aggregation level and that these effects increase mussel resistance to thermal stress.
Highlights
Evidence across a range of taxa describes animal aggregations as an evolutionarily advantageous strategy that provides individual members with benefits such as reduced predation risk, protection from environmental conditions and increased reproductive success, but at the cost of increased intraspecific competition for resources (e.g. [1])
Despite not having an effect on body temperature of isolated individuals, gaping behaviour in mussel beds can significantly modify the habitat and thermal environment experienced by individual organisms composing the aggregation
A field study showed that, during periods of intense heat stress, survival rates of mussels surrounded by gaping mussels are higher than those of isolated individuals or amongst nongaping mussels
Summary
Evidence across a range of taxa describes animal aggregations as an evolutionarily advantageous strategy that provides individual members with benefits such as reduced predation risk, protection from environmental conditions and increased reproductive success, but at the cost of increased intraspecific competition for resources (e.g. [1]). Evidence across a range of taxa describes animal aggregations as an evolutionarily advantageous strategy that provides individual members with benefits such as reduced predation risk, protection from environmental conditions and increased reproductive success, but at the cost of increased intraspecific competition for resources Intertidal, sedentary animals are commonly assumed to be comparable to plant communities that modify their environment primarily through their structure The physical organization of forest and crop systems strongly modifies environmental factors such as wind speed, solar radiation and relative humidity [5]) and for intertidal mussels, the morphological features of individuals and interactions with neighbours can significantly affect their environment. When subjected to extreme environmental conditions, mussels living in beds are predicted to suffer lower mortality rates than those living as isolated individuals [6,7,8]
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