Mapping the drivers of parasitic weed abundance at a national scale : a new approach applied to Striga asiatica in the mid‐west of Madagascar

The parasitic weed genus Striga causes huge losses to crop production in sub‐Saharan Africa, estimated to be in excess of $7 billion per year. There is a paucity of reliable distribution data for Striga ; however, such data are urgently needed to understand current drivers, better target control efforts, as well as to predict future risks. To address this, we developed a methodology to enable rapid, large‐scale monitoring of Striga populations. We used this approach to uncover the factors that currently drive the abundance and distribution of Striga asiatica in Madagascar. Two long‐distance transects were established across the middle‐west region of Madagascar in which S. asiatica abundance in fields adjacent to the road was estimated. Management, crop structure and soil data were also collected. Analysis of the data suggests that crop variety, companion crop and previous crop were correlated with Striga density. A positive relationship between within‐field Striga density and the density of the nearest neighbouring fields indicates that spatial configuration and connectivity of suitable habitats is also important in determining Striga spread. Our results demonstrate that we are able to capture distribution and management data for Striga density at a landscape scale and use this to understand the ecological and agronomic drivers of abundance. The importance of crop varieties and cropping patterns is significant, as these are key socio‐economic elements of Malagasy cropping practices. Therefore, they have the potential to be promoted as readily available control options, rather than novel technologies requiring introduction

Island biogeography, the effects of taxonomic effort and the importance of island niche diversity to single-island endemic species

Island biogeography theory is fundamentally reliant on measuring the number of species per island and hence has taxonomy at its foundation. Yet as a metric used in tests of the theory, island species richness (S) has varied with time according to the level of taxonomic effort (a function of the rate of finding and describing species). Studies using a derivative of S, single-island endemic species richness (SIE S), may be prone to change in taxonomic effort. Decreases or increases in species numbers resulting from taxonomic revision or increased sampling are likely to have a large effect on values of SIE S, as they tend to be smaller than total S for the same island. Using simple biogeography models, we analysed estimates of SIE S in plants, land snails, beetles, and fungi from comprehensive data sets for eight island groups, produced species accumulation curves and applied Bayesian regression over five time periods. Explanatory power differed across taxa, but area and island age were not always the best explanatory variables, and niche diversity appeared to be important. Changing levels of SIE S over time had different effects on models with different taxa and between island archipelagos. The results indicated that the taxonomic effort that determines SIE S is important. However, as this cannot often be quantified, we suggest Bayesian approaches should be more useful than frequentist methods in evaluating SIE S in island biogeography theory. Fundamentally, the article highlights the importance of taxonomy to theoretical biogeography