Mixed effects of an introduced ecosystem engineer on the foraging behavior and habitat selection of predators

Abstract

Invasive ecosystem engineers both positively and negatively affect their recipient ecosystems by generating novel habitats. Many studies have focused on alterations to ecosystem properties and to native species diversity and abundance caused by invasive engineers. However, relatively few studies have documented the extent to which behaviors of native species are affected. The red seaweed Gracilaria vermiculophylla (Rhodophyta) invaded estuaries of the southeastern United States within the last few decades and now provides abundant aboveground vegetative cover on intertidal mudflats that were historically devoid of seaweeds. We hypothesized that G. vermiculophylla would affect the foraging behavior of native shorebirds positively for birds that target seaweed‐associated invertebrates or negatively for birds that target prey on or within the sediment now covered with seaweed. Visual surveys of mudflats >1 ha in size revealed that more shorebirds occurred on mudflats with G. vermiculophylla relative to mudflats without G. vermiculophylla. This increased density was consistent across 7 of 8 species, with the one exception being the semipalmated plover Charadrius semipalmatus. A regression‐based analysis indicated that while algal presence predicted shorebird density, densities of some bird species depended on sediment composition and infaunal invertebrate densities. At smaller spatial scales (200 m2 and <1 m2), experimental removals and additions of G. vermiculophylla and focal observations showed strong variation in behavioral response to G. vermiculophylla among bird species. Birds preferentially foraged in bare mud (e.g., C. semipalmatus), in G. vermiculophylla (e.g., Arenaria interpres), or displayed no preference for either habitat (e.g., Tringa semipalmata). Thus, while the presence of the invasive ecosystem engineer on a mudflat appeared to attract greater numbers of these predators, shorebird species differed in their behavioral responses at the smaller spatial scales that affect their foraging. Our research illuminates the need to account for species identity, individual behavior, and scale when predicting the impacts of invasive species on native communities.

Impact of exotic macroalga on shorebirds varies with foraging specialization and spatial scale

“…Studies of shorebird predator responses to A. vermiculophyllum are limited. In one recent study, Haram et al 2018 observed that shorebird density increased in response to A. vermiculophyllum in the southeastern U.S [7]. Likewise, shorebirds reached peak density on mats of Gracilaria spp.…”

“…Exotic species that modify physical structure of environments exhibit bimodal impacts, depending on whether they increase or decrease habitat heterogeneity [1,3]. When exotic species add complexity or compensate for lost habitat complexity, the density and diversity of native biota increase [1,[3][4][5][6][7]. As heavily human-modified ecosystems become more common in the 21 st century, invasive species may provide conservation opportunities [1,3].…”

“…In some cases invasive macroalgae have devastated benthic communities and water quality [2]; however, most exotic macroalgal species have mixed effects depending on the conditions in the invaded ecosystem and the response variable considered [2]. Agarophyton vermiculophyllum (formally known as Gracilaria vermiculophylla), a cryptically-invasive, habitat-modifying seaweed from east Asia, has established populations throughout the western hemisphere, and since discovery its effects have been perceived as either neutral or "positive" for coastal ecosystems [4,5,7,13,14]. However, examples of negative effects have been documented in particular cases, including seagrass under high temperature and settlement on oysters [15,16].…”

Mengenal Perekayasa Ekosistem

“…Karena itu kelimpahan dan keanekaragaman jenis epibion yang hidup bersama kerang A trapezia dan C taxifolia lebih tinggi daripada yang hidup hanya bersama A trapezia. Meskipun introduksi perekayasa ekosistem dapat dilakukan untuk memperbaiki habitat, namun dalam hal ini perlu diketahui interaksinya dengan spesies asli yang telah ada karena bisa menimbulkan dampak negatif bagi habitat dan spesies asli (Haram et al, 2018).…”

Identifying reliable fitness proxies for growing animals responding to anthropogenic changes

“…The landscape structure is highly important because the provision of refuges affects the effectiveness of responses to predation risk (Heithaus et al, 2009). Predators prefer to forage where there is less cover for prey (Haram et al, 2018) whilst prey select locations with more refuges (Bishop & Byers, 2015). The availability of food in locations that are safe from predators have strong impacts on growth and reproduction in mice (Arthur et al, 2004) and fish (Crowder & Cooper, 1982), and refuge from predation also affect the timing of life history decisions such as maturation (Grof-Tisza et al, 2015).…”