Resource complementation and the response of an insect herbivore to habitat area and fragmentation
Resource complementation and the response of an insect herbivore to habitat area and fragmentation
复制标题
资源互补以及昆虫草食动物对栖息地面积和破碎化的响应
作者：
Kyle J. Haynes;T. Diekötter;T. O. Crist
很少有研究揭示一种局部栖息地类型的面积和破碎化对在同一景观中使用多种栖息地类型的物种的影响。通过实验研究了栖息地面积、栖息地破碎化程度和基质组成对黑斑羚运动和分布的影响。这种蝗虫的成虫优先取食草，但产卵几乎完全在以杂草为主的土壤中。我们比较了不同样地的种群密度，这些样地的面积和三叶草栖息地的碎片化程度以及嵌入三叶草栖息地的基质(草或裸地)的组成不同。此外，还进行了标记再捕获调查，以考察生境面积、破碎化程度和基质组成对样地内三叶草生境中个体的损失和样地内三叶草小区间移动的影响。在以草为基质的样地中，成虫的总密度(在三叶草和基质上的平均值)是裸地的2.2倍，在的样地中，与16平方米的三叶草生境相比，成虫密度高1.8倍。若虫总密度也受较大的三叶草面积的影响，但不受基质组成的影响。在草地基质中的焦点三叶草生境中，小三叶草小区的成虫密度是大三叶草小区的2.1倍。我们的结论是，草基质对成虫密度有积极的影响，但对若虫密度没有影响，因为草和杂草为主的生境可能只为成虫提供补充资源。成虫聚集在草地基质内的小三叶草上，主要归因于单位面积上较大的迁出损失率。此外，这项研究强调，物种对局部栖息地类型面积变化的反应在很大程度上取决于周围景观中补充资源的可用性。
Few studies have disentangled the effects of the area and fragmentation of a focal habitat type on species that use multiple habitat types within a landscape. We experimentally investigated the effects of habitat area, habitat fragmentation, and matrix composition on the movement and distribution of Melanoplus femurrubrum. Adults of this grasshopper feed preferentially on grasses, but oviposit almost exclusively in soil dominated by forbs. We compared population densities among plots that were made to vary in the area and fragmentation of clover habitat and composition of the matrix (grass or bare ground) within which clover habitat was embedded. In addition, a mark-recapture survey was conducted to examine effects of habitat area, fragmentation, and matrix composition on loss of individuals from a plot’s clover habitat and movement between clover subplots within plots. Overall densities of adult M. femurrubrum (averaged over clover and matrix) were 2.2× higher in plots where the matrix was composed of grass as compared to bare ground, and 1.8× higher in plots with 64 compared to 16 m2 of clover habitat. Overall densities of nymphs were also positively influenced by greater clover area, but were unaffected by matrix composition. Within focal clover habitat embedded in grass matrix, adult densities were 2.1× higher in small clover subplots than large clover subplots. We conclude that the grass matrix had a positive effect on adult densities, but not nymph densities, because grass and forb-dominated habitats likely provide complementary resources only for adults. The aggregation of adults on small clover subplots within grass matrix was mainly attributed to a greater rate of emigration loss per unit area. In addition, this study emphasizes that a species’ response to changes in the area of a focal habitat type can depend significantly on the availability of complementary resources in the surrounding landscape.