Well it's almost August and we've had only five females produce below-average sized litters at our down valley locations and, as of today, only one litter (there might be a few more) has emerged at out up-valley locations. If we have more than 30 pups, this will be a good year (by contrast, we had about 130 pups last year and as many as 187 pups in the past decade!). This relatively low productivity will delay the rebound of the population and illustrates a few really interesting things.
1) The importance of body condition and long growing seasons for marmots. Females in poor body condition can't allocate sufficient resources to breed or to produce large litters and we see this effect most pronounced in 'bad' years. In 'good' years, everyone can breed and we don't see the trade-off between litter size and condition expressed.
2) Allee effects! At small populations, strange things happen. For instance we have groups this year with no breeding age females (the female died over the winter) and we have groups without breeding age males. We watched females cycle in preparation for reproduction but they apparently never encountered a male during their fertile window. Such effects are expected in small, fragmented populations and are a huge reason why it's important to keep populations large and connected. Never thought I'd see it commonly happening in our marmot population, but you learn something new every year.
No comments:
Post a Comment