In a previous post on recreation and the Ohlone tiger beetle, I talked about how hikers and bikers are important in creating open, bare ground habitat for the beetles to hunt and find mates. While this is very true, I also mentioned the potential negative effects of recreation on the Ohlone tiger beetle. One negative aspect of recreation on the trails is outright mortality, or squishing of the beetles while they are on the trail. Even though this is completely unintentional, it does happen occasionally.
The other potential negative effect of recreation on the Ohlone tiger beetle is that recreation can disrupt their behavior. We are unsure about this effect, thus calling it “potential” but it is obvious to me that the beetles tend to stop what they are doing and fly away when approached quickly by a human. To test this, I have been conducting bicycle trails where I watch how a beetle, or mating pair of beetles, changes its behavior when a bike rides by. I’ve been doing this with bikes at very slow speeds (5-10 mph) and a normal-fast speed (20 mph). That way I’ll know if telling bikes to slow down in beetle habitat actually makes a difference! I’ll also test what hikers do to the beetle behavior.
One behavior I’m curious about getting disrupted by recreation is mating and mate guarding by males. Mate guarding happens when a male physically stays on a female after they are finished actually mating. The male stays on the female to guard her from other potential mates that may replace his sperm! Sperm in the beetles doesn’t fertilize the eggs right away like it does in humans. In fact, the female stores sperm in something called a spermatheca until she is ready to lay her eggs. Sperm only fertilizes the eggs as they exit the female’s body.
If another male mates with a female right after the first male, the second male’s sperm could end up replacing the first male’s sperm as the sperm that actually fertilizes the eggs! Pretty cool. That is why males have an incentive to guard females they mate with, at least for a while. Males that mate guard longer will most likely father more offspring. Because mate guarding evolved in this beetle, that means the benefits of mate guarding out weigh the risk of being eaten by predators while guarding. Thus, interruptions by recreationists could decrease the chance that fit males transfer sperm and father offspring, potentially decreasing the fitness of the population over the long term!