Arthropods are not declining but are responsive to disturbance in the Luquillo Experimental Forest, Puerto Rico

Abstract

A number of recent studies have documented long-term declines in abundances of important arthropod groups, primarily in Europe and North America. These declines are generally attributed to habitat loss, but a recent study [B.C. Lister, A. Garcia, Proc. Natl. Acad. Sci. USA 115, E10397–E10406 (2018)] from the Luquillo Experimental Forest (LEF) in Puerto Rico attributed declines to global warming. We analyze arthropod data from the LEF to evaluate long-term trends within the context of hurricane-induced disturbance, secondary succession, and temporal variation in temperature. Our analyses demonstrate that responses to hurricane-induced disturbance and ensuing succession were the primary factors that affected total canopy arthropod abundances on host trees, as well as walkingstick abundance on understory shrubs. Ambient and understory temperatures played secondary roles for particular arthropod species, but populations were just as likely to increase as they were to decrease in abundance with increasing temperature. The LEF is a hurricane-mediated system, with major hurricanes effecting changes in temperature that are larger than those induced thus far by global climate change. To persist, arthropods in the LEF must contend with the considerable variation in abiotic conditions associated with repeated, large-scale, and increasingly frequent pulse disturbances. Consequently, they are likely to be well-adapted to the effects of climate change, at least over the short term. Total abundance of canopy arthropods after Hurricane Maria has risen to levels comparable to the peak after Hurricane Hugo. Although the abundances of some taxa have declined over the 29-y period, others have increased, reflecting species turnover in response to disturbance and secondary succession.

Sensitivity of Tropical Insectivorous Birds to the Anthropocene: A Review of Multiple Mechanisms and Conservation Implications

“…Raven and Wagner (2021) make a compelling case for agricultural intensification coupled with climate change as the major causes of insect declines globally to date, which predicts accelerating tropical insect declines given agricultural, and human population trends. Sekercioglu et al (2002) failed to find evidence that insect declines caused bird declines, whereas Garcia (2018, 2019) but see Willig et al, 2019;Schowalter et al, 2021) argued for insect declines causing vertebrate predator declines in Puerto Rico. Wagner (2020) argues that scant evidence is available presently to link bird declines to insect declines.…”

Long‐term trends in gastropod abundance and biodiversity: Disentangling effects of press versus pulse disturbances

“…Many taxa in other environments are declining in abundance, likely in response to a combination of biocides, habitat loss and fragmentation, and an increasingly warm world (Dirzo et al, 2014;Hallman et al, 2017;Rosenberg et al, 2019;Sánchez-Bayo & Wyckhuys, 2019;Thomas, 2004;Wagner, 2020), thereby generating alarm about a pending mass extinction and collapse of ecological systems across the planet. In contrast to this phenomenon, declines have not been detected for arthropods in the sub-canopy (Schowalter et al, 2021;Willig et al, 2019) or for dominant vertebrate groups in tabonuco forest of Puerto Rico (Willig et al, 2019).…”

Potential Reasons for Insect Decline

“…The insect declines potentially have created global ecological and economic consequences. Not all insects are declining and many lineages have not changed rather increased in abundance [15,16]. For instance: In Great Britain many species of moths have expanded in their range or population size [17]; numerous temperate insects, presumably limited by winter temperatures, have increased their abundance and range, in response to warmer global temperatures [14]; anthropophilic and humanassisted taxa, which include many pollinators, such as the western honey bee (Apis mellifera Linnaeus) in North America, thrive well due to their associations with humans; abundance of freshwater insects attributed to clean water legislation, in both Europe and North America [18].…”