A discrete reaction-diffusion model was used to estimate long-term equilibrium populations of a hypothetical species inhabiting patchy landscapes to examine the relative importance of habitat amount and arrangement in explaining population size. When examined over a broad range of habitat amounts and arrangements, population size was largely determined by a pure amount effect (proportion of habitat in the landscape accounted for >96% of the total variation compared to <1% for the arrangement main effect). However, population response deviated from a pure amount effect as coverage was reduced below 30%-50%. That deviation coincided with a persistence threshold as indicated by a rapid decline in the probability of landscapes supporting viable populations. When we partitioned experimental landscapes into sets of "above" and "below" persistence threshold, habitat arrangement became an important factor in explaining population size below threshold conditions. Regression analysis on below-threshold landscapes using explicit measures of landscape structure (after removing the covariation with habitat amount) indicated that arrangement variables accounted for 33%-39% of the variation in population size, compared to 27%-49% for habitat amount. Thus, habitat arrangement effects became important when species persistence became uncertain due to dispersal mortality.

-A study was carried out to find out whether more intense treatment (both medical and revascularisation) is targeted towards higherrisk patients with acute coronary syndromes. A prospective UK registry of patients admitted with non-ST elevation acute coronary syndromes was established to examine practice patterns and clinical outcomes with respect to the risk profile of the patients. Clinically important high-risk subgroups included the elderly, diabetics, those with heart failure and those with ST depression or bundle branch block on the presenting ECG. Elderly patients were less likely to receive evidence-based treatments, including beta blockers, statins and revascularisation. Diabetics received more revascularisation procedures but the overall revascularisation rate was low. Heart failure patients received less evidence-based treatment, with the exception of angiotensin-converting enzyme (ACE) inhibitors. Heparin was used less frequently in those with a normal ECG, although rates of revascularisation were not different when compared with those with ECG abnormalities. The conclusions of the study were that groups of patients with particularly high event rates are readily identified by their clinical characteristics, but use of evidence-based treatments and invasive investigations do not appear to be targeted towards those at greatest risk. Risk stratification and the appropriate application of treatments for patients with acute coronary syndromes need to be reviewed in the clinical setting.