Climatic seasonality may affect ecological network structure: Food webs and mutualistic networks

Abstract

Ecological networks exhibit non-random structural patterns, such as modularity and nestedness, which determine ecosystem stability with species diversity and connectance. Such structure-stability relationships are well known. However, another important perspective is less well understood: the relationship between the environment and structure. Inspired by theoretical studies that suggest that network structure can change due to environmental variability, we collected data on a number of empirical food webs and mutualistic networks and evaluated the effect of climatic seasonality on ecological network structure. As expected, we found that climatic seasonality affects ecological network structure. In particular, an increase in modularity due to climatic seasonality was observed in food webs; however, it is debatable whether this occurs in mutualistic networks. Interestingly, the type of climatic seasonality that affects network structure differs with ecosystem type. Rainfall and temperature seasonality influence freshwater food webs and mutualistic networks, respectively; food webs are smaller, and more modular, with increasing rainfall seasonality. Mutualistic networks exhibit a higher diversity (particularly of animals) with increasing temperature seasonality. These results confirm the theoretical prediction that the stability increases with greater perturbation. Although these results are still debatable because of several limitations in the data analysis, they may enhance our understanding of environment-structure relationships.

Human Impacts and Climate Change Influence Nestedness and Modularity in Food-Web and Mutualistic Networks

“…Data for the food-web, pollination, and seed-dispersal networks were collected from around the world ( Fig 1 ). It must be noted, however, that the data was likely to be somewhat biased; for one, research on ecological networks tends to derive from several specific countries and not others (see [ 29 ] for details), a sampling bias that suggests spatial autocorrelation in the data. As such, we adopted a spatial eigenvector mapping (SEVM) modeling approach during data analysis (see the following sections) in order to remove any inherent spatial autocorrelation, in addition to application of ordinary least squares (OLS) regression analysis (see Materials and Methods ).…”

“…The importance of environmental factors are often discussed in the context of ecosystem stability [ 23 , 24 ]; many previous studies [ 25 , 26 ] have focused on the association between the environment and ecological network structure, with several focusing specifically on the influence of the environment on nestedness/modularity. Several studies [ 27 – 30 ] have reported the relationship between climatic parameters and nestedness and modularity in mutualistic networks and food webs; for example, nestedness in pollination networks was found to decrease with annual precipitation [ 27 ], whereas modularity in seed-dispersal networks increased with temperature seasonality [ 28 ], and a positive correlation between modularity and precipitation seasonality was observed in food webs [ 29 ]. Previously [ 29 ], we demonstrated that climate seasonality affects ecological networks, and that the type of climatic seasonality influencing network structure differs among ecosystems; for example, network properties in freshwater ecosystems were mainly affected by rainfall seasonality but primarily by temperature seasonality in terrestrial ecosystems.…”

Climate drives plant–pollinator interactions even along small‐scale climate gradients: the case of the Aegean

“…Similarly, Takemoto et al . () found seasonality to affect the modularity of food webs, but their results were equivocal regarding the role of seasonality on mutualistic networks. Our results indicate that the increased role of climate is associated with mean climatic values ( viz .…”

Availability of food resources and habitat structure shape the individual‐resource network of a Neotropical marsupial

“…However, to our knowledge, there are no studies testing for direct relatedness of habitat structure and nestedness, especially considering within‐population networks. Tests directly relating the role of spatio‐temporal components on network structure are more common in macroecological studies, showing for example, relationship of annual precipitation, temperature seasonality, and latitude with nestedness (Takemoto, Kanamaru, & Feng, ; Trøjelsgaard & Olesen, ). At smaller scales, it has been shown (but not tested for direct relationship) that variation in biotic and abiotic factors (e.g., heterogeneity, vegetation productivity, temperature, and precipitation) increases nestedness, playing a larger role in comparison to evolutionary constraints (Robinson, Hauzy, Loeuille, & Albrectsen, ; Thompson, Adam, Hultgren, & Thacker, ).…”