Heterogeneous patterns of abundance of epigeic arthropod taxa along a major elevation gradient

Species diversity is the variable most commonly studied in recent ecological research. Ecological processes, however, are driven by individuals and affected by their abundances. Understanding the variation in animal abundances along climatic gradients is important for predicting changes in ecosystem processes under global warming. High abundances make arthropods, despite their small body sizes, important actors in food webs, yet abundance distributions of major arthropod taxa along climatic gradients remain poorly documented. We sampled arthropod assemblages in disturbed and undisturbed vegetation types along an elevational gradient of 860-4550m asl on the southern slopes of Mt. Kilimanjaro, Tanzania. In our analysis, we focused on 13 taxa of arthropods that represented three major functional groups: predators, herbivores, and decomposers. Abundance patterns were unimodal for most of the taxa and functional groups, including decomposer arthropods, and most of them peaked at low elevations in lower montane forest. When we assigned beetles to functional groups, however, decomposer beetle abundances declined almost linearly, and abundances of predator beetles (ca. 2400m asl) and herbivore beetles (ca. 3000m asl, undisturbed vegetation) peaked at higher elevations and exhibited unimodal patterns. Temperature, not primary productivity, was the best predictor of abundance for most of the taxa and groups. Disturbance was only of minor importance. Our results revealed different trends in the response of arthropod abundance along the elevational gradient that depended on the level of taxonomic and functional resolution. This highlights the need for more comparisons of different taxa along the same climatic gradients. Ufupisho Utofauti wa spishi ni kawaida ilivyoripotiwa katika makala ya hivi karibuni ya utafiti wa ikolojia. Mifumo ya ikolojia, hata hivyo, inaendeshwa na viumbe binafsi. Wingi wa athropoda, licha ya udogo wa maumbo yao huwafanya kuwa watendaji muhimu katika mfumo wa chakula. Uelewa wa tofauti katika wingi wa wanyama katika tabia nchi tofauti ni muhimu kwa ajili ya utabiri wa mabadiliko ya utendaji kazi wa mifumo ikolojia kutokana na ongezeko la joto duniani. Licha ya hili, data kuhusu mgawanyo wa wingi wa arthopoda katika tabia nchi tofauti bado ni chache. Tulikusanya sampuli za athropoda kutoka kwenye maeneo yasio na uoto wa asili na yale yenye uoto wa asili katika mwinuko wa kati ya mita 860 hadi mita 4550 UB kwenye mteremko wa upande kusini wa Mlima Kilimanjaro huko Tanzania. Katika uchambuzi wetu, sisi tulilenga katika aina 13 tofauti za athropoda zinazowakilisha makundi matatu makuu ya kazi: wawindaji, wala mimea na waozeshaji. Aina nyingi zilionyesha mtindo wa aina moja wa wingi, kilele kikiwa katika maeneo ya mwinuko wa chini. Wakati aina zilipopangwa katika makundi ya kazi, wawindaji na waozeshaji walionyesha kilele kidogo katika au chini ya mwinuko wa mita 1500 UB na kupungua katika wingi kwenye miinuko ya juu. Waozeshaji walionyesha kilele tofauti kwenye mita 1500 UB. Tulipowapanga mende-kibyongo kwenye makundi ya kazi, hata hivyo, waozeshaji walipungua kimstari, na wawindaji (mita 2400 UB) na wala mimea (mita 3000 UB, uoto wa asili) walionyesha mtawanyiko wa aina moja, na vilele zaidi juu ya mwinuko. Joto, na si tija msingi, ndio lilikuwa mbashiri bora wa wingi wa aina na makundi. Usumbufu ulikuwa na umuhimu kidogo. Kwa kumalizia, tumeona tofauti katika mwenendo wa wingi wa athropoda katika mwinuko unategemea aina pamoja na kundi la kazi. Hii inaonyesha haja ya kulinganisha zaidi aina mbalimbali kwenye haya mazingira.