Floodplain ants show a stronger response to an extensive flood than to variations in fallen‐timber load

Abstract

Understanding how species respond to differences in resource availability is critical to managing biodiversity under the increasing pressures associated with climate change and growing human populations. Over the last century, the floodplain forests of Australia's largest river system, the Murray-Darling Basin, have been much affected by intensive harvesting of timber and firewood, and increasingly stressed by river regulation and, recently, an extended drought. Fallen timber -logs and shed branches -is known to play a key role in the ecology of several important species on these floodplains. Here, we monitored the response of the ant assemblages of a floodplain forest along the Murray River to a large-scale (34 ha) experimental manipulation of fallen-timber load (0 to 80 t ha -1 ) over 4 years. The forest was subjected to an incidental, extensive flood that enabled us to examine how two important stressors (timber removal and river regulation) affect ant assemblages. Ants showed little response to the proximity of fallen timber within plots, prior to the flood, or to different loads among plots, unlike other floodplain biota. After the flood, both ant abundance and species richness increased and species composition changed. However, this increase in species richness after flooding was less pronounced in plots with higher amounts of fallen timber. Managing river red gum forest using a mosaic of flood regimes, more representative of historical conditions, is likely to be the most effective way to maintain and enhance the diversity of ants and other biota on these important floodplains.

Conservation implications of ecological responses to extreme weather and climate events

“…These responses serve as a reminder that natural disturbances from extreme events often play a critical role in maintaining the structure and function of many ecosystems and life history strategies (Attiwill, ; McMahon et al, ; Whittaker, Willis, & Field, ). Some positive responses that were common yet temporary included cyclone events leading to increased abundances of bird species that prefer regenerating habitat (e.g., Brown, Sherry, & Harris, ; Freeman et al, ), and cyclones and floods leading to increased richness of fish and invertebrate species (e.g., Gerisch, Dziock, Schanowski, Ilg, & Henle, ; Horrocks, Cunningham, O'Dowd, Thomson, & Mac Nally, ; Kano et al, ). Increases in fish and invertebrate richness were typically due to higher food availability in disturbed areas, or flooding events facilitating colonization by species downstream.…”

Ecological effects of extreme climatic events on riverine ecosystems: insights from Australia

“…Floods influence ecosystem processes, affecting within‐channel productivity, particulate organic matter retention, decomposition, nutrient transformations and microbial processes (Baldwin & Mitchell, ; Hladyz et al ., ). Floods also affect terrestrial floodplain biota (Horrocks et al ., ) and influence surface water and groundwater quality and recharge (Cendón et al ., ) (Fig. ).…”

Assessment and planning for emerging impacts of climate change on species

“…Brown, Sherry, & Harris, 2011;Freeman et al, 2008), and cyclones and floods leading to increased richness of fish and invertebrate species (e.g. (Gerisch, Dziock, Schanowski, Ilg, & Henle, 2012;Horrocks, Cunningham, O'Dowd, Thomson, & Mac Nally, 2012;Kano et al, 2011). Increases in fish and invertebrate richness were typically due to higher food availability in disturbed areas, or flooding events facilitating colonisation by species downstream.…”