Spatial complementarity and the coexistence of species

Coexistence of apparently similar species remains an enduring paradox in ecology. Spatial structure has been predicted to enable coexistence even when population-level models predict competitive exclusion if it causes each species to limit its own population more than that of its competitor. Nevertheless, existing hypotheses conflict with regard to whether clustering favours or precludes coexistence. The spatial segregation hypothesis predicts that in clustered populations the frequency of intra-specific interactions will be increased, causing each species to be self-limiting. Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade. In this study we create an individual-based model in homogeneous two-dimensional space for two putative sessile species differing only in their demographic rates and the range and strength of their competitive interactions. We fully characterise the parameter space within which coexistence occurs beyond population-level predictions, thereby revealing a region of coexistence generated by a previously-unrecognised process which we term the triadic mechanism. Here coexistence occurs due to the ability of a second generation of offspring of the rarer species to escape competition from their ancestors. We diagnose the conditions under which each of three spatial coexistence mechanisms operates and their characteristic spatial signatures. Deriving insights from a novel metric — ecological pressure — we demonstrate that coexistence is not solely determined by features of the numerically-dominant species. This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community. Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation

Model Risk Management. Le prassi e il modello a tendere.

I modelli hanno assunto un ruolo pervasivo nell’operatività bancaria configurandosi come driver essenziali nel decision making sia in ambito regolamentare che gestionale, e questa considerazione, seppur con caratterizzazioni diverse, risulta valida sia per banche “significant” che “less significant”. Si evidenzia che il numero e la complessità dei modelli hanno raggiunto un livello di ampiezza tale da richiederne una gestione dedicata e strumenti specifici per evitare che la base decisionale si poggi su algoritmi, dati o elaborazioni non adeguati. Oltre alla complessità intrinseca dei modelli, si aggiunge una crescente interconnessione tra gli stessi per cui le criticità di un modello possono riverberarsi sui modelli collegati con effetti poco prevedibili. Le mutevoli condizioni di contesto (accentuate dall’emergenza Covid), hanno ulteriormente amplificato l’esigenza di ridurre la distanza tra l’identificazione delle criticità sui modelli, la presa in carico delle azioni correttive, il relativo monitoraggio e il rilascio degli interventi. Una catena di trasmissione non adeguata comporta inevitabilmente tempi di risposta più lunghi, con modelli che non sono in grado di rappresentare adeguatamente il contesto operativo

In vivo manipulation of human breast cancer growth by estrogens and growth hormone: kinetic and clinical results.

Since 1983, a series of experimental and clinical studies have been carried out on the possibility of enhancing the chemotherapy effectiveness in breast cancer by expanding the fraction of cycling cells. Theoretically estrogens should recruit breast cancer cells and this fact should result in a higher killing efficiency of antiproliferative drugs. Actually it has been clearly shown, by means of the thymidine labeling index and primer-dependent alpha-DNA polymerase assay, that low doses of diethylstilbesterol are able to increase the tumor proliferative activity of human breast cancer in vivo (estrogenic recruitment). Three randomized trials have been carried out (one in locally advanced and two in metastatic breast cancer) comparing conventional polychemotherapy vs chemotherapy with estrogenic recruitment. Only limited advantages have been observed in these trials. Searching for new modalities of kinetic manipulation of tumors, recombinant human growth hormone has been employed in a pilot study: the preliminary results indicate that it largely enhances tumor proliferative activity, suggesting the possibility of employing a growth factor system to increase chemosensitivity

Chemotherapy with estrogenic recruitment and surgery in locally advanced breast cancer: clinical and cytokinetic results.

Thirty-nine patients with locally advanced breast cancer (T3b-4, N1-3 or inflammatory carcinoma) received 3 cycles of induction chemotherapy with estrogenic recruitment before surgery. The therapeutic regimen consisted of diethylstilbestrol (DES) orally on days 1-3, 5-Fluorouracil + Doxorubicin + Cyclophosphamide on day 4 q 21 days (DES-FAC). After surgery 6 additional cycles of chemotherapy (3 DES-FAC alternating with 3 DES-CMF with Methotrexate + F and C as in FAC) were administered. The objective response rate was 71.8\% with 15.4\% CR, and 56.4\% PR; after surgery 36/39 (92.3\%) patients were rendered disease-free. So far, 13 of 26 patients in stage IIIb have relapsed (9 of 13 with inflammatory carcinomas). Three-year survival and progression-free survival are 60\% and 53.5\%, respectively. Twenty-three of the 39 patients were subjected to serial tumor biopsies during the first DES-FAC regimen to allow for tumor-cell kinetic studies during DES and chemotherapy. A significant estrogenic recruitment occurred in 16 patients (69.6\%), irrespective of estrogen-receptor status. At surgery, 3-4 weeks after induction chemotherapy, tumor proliferative activity was significantly depressed in comparison to basal values. These results indicate that breast cancer cells can be recruited in vivo with DES and that chemotherapy following estrogenic stimulation is effective and feasible with acceptable toxicity