To go beyond univariate regressions of population abundance on ambient temperature, we constructed multiple quasi-Poisson regressions using independent variables identified by a hierarchical partitioning (HP) analysis ( 32, 33). P < 0.05 indicates a statistically significant regression. Pr(χ) is the result of a likelihood-ratio χ 2 test of whether the independent variable improves the model beyond an intercept-only model. The 95% confidence intervals are shown around the best-fit regression lines. ( D) Quasi-Poisson regression of the total number of birds captured during Waide’s ( 31) 4-d sessions vs. ( C) Quasi-Poisson regression for the total number of birds captured during equal length, 4-d sessions of mist netting ( 31) near the El Verde Field Station against the period when the mist netting was conducted. coqui individuals against MnMaxT during the time periods when Stewart’s censuses were conducted. ( B) Quasi-Poisson regression of the estimated number of E. coqui individuals against time from censuses conducted by Stewart ( 28) in the Activity Transect. ( A) Quasi-Poisson regression of estimated total number of E. coqui and birds near the El Verde Field station. S8 K), suggesting that our measure reflects significant exposure to extremes rather than ephemeral spikes in temperature ( 6, 20).įig. However, there was a significant positive linear regression of proportion of days per year when the temperature equaled or exceeded 29 ☌ on MnMaxT at El Verde ( SI Appendix, Fig. Because data from the Bisley and El Verde stations record just one maximum and minimum temperature per 24-h period, we could not calculate the duration of time that temperatures remained above the 29 ☌ extreme. While average temperatures increased 8–10% over the same period, the proportion of extreme temperatures increased 14 times. At the Bisley station, the proportion of maximum daily temperatures equal to or exceeding 29.0 ☌ grew steadily from the 1990s until 2015, with the proportion averaging 0.–1994 and 0.–2015. At El Verde the proportion of maximum daily temperatures equal to or exceeding 29.0 ☌ increased significantly between 19 ( SI Appendix, Fig. Results Climate Trends in the Luquillo Forest.Īs several authors have pointed out, increased exposure to extreme temperatures may have a greater impact on fitness than gradual increases in average temperatures ( 6, 19, 20). Here we analyze long-term data on climate change, arthropod abundance, and insectivores within the Luquillo rainforest in northeastern Puerto Rico, with the aim of determining if increases in ambient temperature may have driven reductions in arthropod numbers and associated decreases in consumer abundance. While demonstrated impacts of climate change on tropical forests include reductions in plant diversity ( 14), changes in plant species composition ( 15), and increases in tree growth, mortality, and biomass ( 16), little is known about the impact of climate warming on rainforest arthropods ( 17, 18). Studies documenting declines in insects have focused on temperate species ( 10– 13), and have identified climate warming, along with habitat disturbance and insecticides, as primary causal mechanisms ( 9, 10). While El Niño/Southern Oscillation influences the abundance of forest arthropods, climate warming is the major driver of reductions in arthropod abundance, indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web.Īlthough arthropods comprise more than two-thirds of all terrestrial species and are centrally important to the ecological well-being of the Earth’s ecosystems, long-term data on population abundance and extinction rates are severely limited ( 9). We also document parallel decreases in Luquillo’s insectivorous lizards, frogs, and birds. Analysis of long-term data on canopy arthropods and walking sticks taken as part of the Luquillo Long-Term Ecological Research program revealed sustained declines in abundance over two decades, as well as negative regressions of abundance on mean maximum temperatures. Using the same study area and methods employed by Lister in the 1970s, we discovered that the dry weight biomass of arthropods captured in sweep samples had declined 4 to 8 times, and 30 to 60 times in sticky traps. During this time, mean maximum temperatures have risen by 2.0 ☌. Here we analyze data on arthropod and insectivore abundances taken between 19 at two midelevation habitats in Puerto Rico’s Luquillo rainforest. Although arthropods comprise over two-thirds of terrestrial species, information on their abundance and extinction rates in tropical habitats is severely limited. If these predictions are realized, climate warming may have a more profound impact on the functioning and diversity of tropical forests than currently anticipated. A number of studies indicate that tropical arthropods should be particularly vulnerable to climate warming.
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